<p>The internet has informed me one <strong>mil</strong> is a measurement that equals one-thousandth of an inch (0.001 inch) or 0.0254 mm. You can convert any length unit into mils via <a href="https://www.google.com/search?q=google%20mil%20to%20inch" rel="nofollow noreferrer">Google's length unit conversion</a> (<em>Google labels it <strong>Thousandth of an inch</strong> instead of <strong>mil</strong></em>).</p>
<p>Per the comments below, there are some British English applications where the term <strong>thou</strong> (short for thousands) is used instead of <strong>mil</strong>.</p>
<p>I also learned that to convert between <strong>mil</strong> and <strong>gauge</strong> one can take the number of mil and multiply by 100; thus a 2 mil thickness converts to 200 gauge (<a href="https://www.uline.com/CustomerService/ULINE_FAQ_Ans?FAQ_ID=49" rel="nofollow noreferrer">according to ULine's website</a>).</p>
<p>Explanation of <strong>mil</strong> I found from a helpful <a href="https://www.globalplasticsheeting.com/mil-thickness-compared-to-mm-millimeter-and-inches" rel="nofollow noreferrer">plastic sheeting website</a>:</p>
<blockquote>
<p><strong>How does mil thickness compare to mm (millimeter) and inches? What does mil stand for in measurement?</strong></p>
<p>Plastic sheeting is measured in mils.  A mil is a measurement that equals one-thousandth of an inch, or 0.001 inch. One mil also equals 0.0254 mm (millimeter). Thus a mil is not the same thickness as a millimeter. The term &quot;mil&quot; is not an abbreviation but a unit of measure.The chart below gives you an idea of mils to millimeters to inches. An every day trash bag ranges between 1.2 mils and 1.7 mils. A much stronger trash bag that offers better tear resistance is between 3 mils and 6 mils. A credit card is around 30 mils thick while a common deck of playing cards including the box is approximately .75 inches thick or 750 mils.</p>
<div class="s-table-container">
<table class="s-table">
<thead>
<tr>
<th>mil</th>
<th>mm</th>
<th>inch</th>
<th>Item</th>
</tr>
</thead>
<tbody>
<tr>
<td>1</td>
<td>0.0254</td>
<td>0.001</td>
<td></td>
</tr>
<tr>
<td>3</td>
<td>0.07619</td>
<td>0.003</td>
<td></td>
</tr>
<tr>
<td>6</td>
<td>0.152399</td>
<td>0.006</td>
<td></td>
</tr>
<tr>
<td>10</td>
<td>0.254</td>
<td>0.01 (1/64 in)</td>
<td></td>
</tr>
<tr>
<td>15</td>
<td>0.381</td>
<td>0.015</td>
<td></td>
</tr>
<tr>
<td>20</td>
<td>0.508</td>
<td>0.02</td>
<td></td>
</tr>
<tr>
<td>30</td>
<td>0.762</td>
<td>0.03  (1/32 in)</td>
<td>Credit card</td>
</tr>
<tr>
<td>60</td>
<td>1.524</td>
<td>0.06  (1/16 in)</td>
<td></td>
</tr>
<tr>
<td>100</td>
<td>2.54</td>
<td>0.1  (3/32 in)</td>
<td></td>
</tr>
</tbody>
</table>
</div></blockquote>
<p>Additionally, the same website had some <a href="https://www.globalplasticsheeting.com/thickness-of-plastic-sheeting" rel="nofollow noreferrer">helpful information for visualizing thickness in mils</a>:</p>
<blockquote>
<p><strong>Thickness of Plastic Sheeting</strong></p>
<p>Plastic Sheeting [...] is rated with the term, &quot;mil&quot;. [...] Most human hair is  One-thousandth of inch, or 0.001 inch [or 1 mil].  The most common size in the thickness rating for plastic sheeting is 6 mil. This is 6-thousandths of an inch, or 0.006 inch. Generally, the thicker the plastic, the stronger it is.  If it has string/scrim reinforcement, then the string within the plastic will give it added strength. Depending on the application, the composition of the plastic can play a big role regardless of the thickness.  For example, additives added to the plastic such as the fire retardant (FR) additive may play a more significant role than the thickness of the plastic if the job requires FR plastic.</p>
<p><em>Note that the term &quot; heavy gauge&quot; plastic is not to be confused with &quot;heavy mil&quot; referring to heavy plastic sheeting. The term &quot;gauge&quot; refers to the thickness of metal. It really doesn't apply to plastic sheeting/ plastic sheets.</em></p>
<div class="s-table-container">
<table class="s-table">
<thead>
<tr>
<th>Thickness of Plastic Sheeting</th>
<th>Common item for comparison</th>
</tr>
</thead>
<tbody>
<tr>
<td>75 mil</td>
<td>U.S. Nickel</td>
</tr>
<tr>
<td>60 mil</td>
<td>U.S. Penny</td>
</tr>
<tr>
<td>50 mil</td>
<td>U.S. Dime</td>
</tr>
<tr>
<td>10 mil</td>
<td>Business card</td>
</tr>
<tr>
<td>6 mil</td>
<td>white trash bag used in kitchens</td>
</tr>
<tr>
<td>4 mil</td>
<td>standard piece of paper</td>
</tr>
</tbody>
</table>
</div></blockquote>

CC BY-SA 4.0
2022-02-14T17:24:42.023Z
That is definitely news to me. In non-Imperial measurement countries, such as the one I live in, I have always used mil as millimetre, because we only use metric measurements for this sort of thing.
Rory Alsop
CC BY-SA 4.0
2022-02-14T19:39:49.407Z
Mil ( 0.001 in.) very commonly used world wide when discussing corrosion amount or rates. Also thickness of protective coatings ( paint).
blacksmith37
CC BY-SA 4.0
2022-02-14T21:02:20.223Z
@RoryAlsop hence 0.001" being called "thou" in British English. "Mil" as used here is essentially an Americanism  that has gone international in some uses
Chris H
CC BY-SA 4.0
2022-02-15T05:51:37.867Z
I totally agree with Rory Alsop; I thought mil was a different abbreviation for millimetre. Kind of makes sense though... If you base your unit of measurement on the length of 3 corns of barley and you want to derive a much smaller unit of measurement you "mill" them down  XD
Elmy
CC BY-SA 4.0
2022-02-15T08:17:01.273Z
@chris yet mil predates English usage in other languages like Spanish.
cde
CC BY-SA 4.0
2022-02-15T08:42:15.603Z
@cde it's straight from Latin so it's not really surprising; it's also the logical choice in metric /SI prefixes. I would put the onus on the people using archaic units to deal with the confusion. Here in the UK we use both metric and imperial, but our modern engineering is firmly metric
Chris H
CC BY-SA 4.0
2022-02-15T09:08:43.907Z
@chris so you are used to millimeters right?  A thousands of a meter. Mil predates Thou in English usage by almost 100 years. And English the klepto it is imported thou from Germanic while most SI units are latin in nature.
cde
CC BY-SA 4.0
2022-02-15T10:16:07.027Z
@cde Yes, I'm used to mm, and nearly all my measuring kit is metric-only.  Whitworth was apparently using "thou" before 1850 (though I can only find reference to "thousandths" in sources I have access to), and was one of the first to propose working in decimal inches.  He would have had the choice of Latinate or Germanic vocabulary to derive his terminology. "mil" from milliradian has several similar angular meanings as well.
Chris H
CC BY-SA 4.0
2022-02-15T10:31:24.880Z
It bugged me that the first table gives 10 mil, which is 10/1000th or 1/100th of an inch, equal to 1/64th of an inch, which is 0.015625 inches, or about 15 mils. But it's not a transcription error, so I have to wonder if it's an error in the source or whether it's really conventional wisdom in the USC system. As a side note for @cde, most SI prefixes derive from Greek, with a handful from Latin, French, Spanish or Danish.
AmiralPatate
CC BY-SA 4.0
2022-02-15T13:44:39.550Z
@AmiralPatate it's an error in the table, I reckon a flawed attempt to give some approximate conversions.  All the fractional values are off - obviously as sums of powers of 1/2 can't represent powers of 1/10 precisely - but some by more than others. The one you spotted is too far off to be a convenient approximation given that 15 mil (0.381mm) is listed and 1/64" is 0.397mm.  I do just enough with US-built kit to have a table of decimal inches, fractional inches, and mm on the wall next to my desk here in work.
Chris H
CC BY-SA 4.0
2022-02-15T13:46:14.517Z
Also *The term "mil" is not an abbreviation but a unit of measure* from the source is wrong.  At best they could say "no longer an abbreviation" but the full form "milli-inches" is often seen in old documents
Chris H
CC BY-SA 4.0
2022-02-15T14:49:56.193Z
3 mil is the thickness of a heavy-duty "contractor" trash bag, not regular white kitchen bags. In case you want another couple reference points, I have 0.31 mil plastic sheeting to cover windows while painting; it's light and crinkly, flimsier than a grocery sack. 6 mil is one of the heaviest I've commonly found in big-box hardware stores (I used it to seal off lead abatement work).
MissMonicaE
CC BY-SA 4.0
2022-02-15T16:26:09.597Z
Mil are *never* used as short version for milimeters in my experience (in speech, yes, written, never), but you'll see it a lot in printed circuit board (PCB) design. Many measurements on a PCB are in mil.
Mast
CC BY-SA 4.0
2022-02-14T17:02:33.967Z
2022-02-16T13:04:05.837Z
2022-02-16T13:04:05.837Z
Wimateeka
<p>This is basic English etymology:</p>
<blockquote>
<p>mil (n.)</p>
</blockquote>
<blockquote>
<p>1721, in per mil &quot;per thousand,&quot; from Latin mille &quot;thousand&quot; (see million); compare percent. As a unit of length for diameter of wire (equal to .001 of an inch) it is attested from 1891; as a unit of angular measure it is recorded by 1907. <a href="https://www.etymonline.com/word/mil" rel="nofollow noreferrer">https://www.etymonline.com/word/mil</a></p>
</blockquote>
<p>Like a large part of English and typical imperial units, mil comes from Latin for thousands. <em><strong>As in One Thousands of an inch.</strong></em> Mil is also the root word for million. And milli as in milliamps or millimeters, in metric units. Mil is a the root of them all.</p>
<p>This is also true for other languages like Spanish, where a mil pesos for example means a thousand as in One Thousand Dollars.</p>

CC BY-SA 4.0
2022-02-15T08:12:14.980Z
2022-02-15T08:12:14.980Z
cde
<p>&quot;mil&quot; is not a standardised unit, and whilst it can usually be interpreted as &quot;one thousandth&quot; of something the only safe course of action is to ask the supplier for clarification.</p>
<p>Having said that, it's <em>probably</em> safe to interpret it by context (e.g. paper would be unlikely to be several millimetres thick) and by reference to the location of the seller (Americans use English units, just about everybody else uses metric units). But you'd be most unwise to rely on that if gross misjudgement would be expensive: a court would probably not consider &quot;I assumed that...&quot; to be an adequate level of certainty.</p>

CC BY-SA 4.0
2022-02-15T16:28:05.653Z
This answer is wrong. In certain industries, mil is used as a standardised unit. Perhaps not SI standardised, but in those sectors (like electronics R&D) it's very standard. 0.001".
Mast
CC BY-SA 4.0
2022-02-16T11:12:15.117Z
@Mast There are certain environments in which "Furlongs per Fortnight" and measuring lengths by comparing them with that of a London bus are popularly accepted. Quoting a length in mil has no more standing than that.
Mark Morgan Lloyd
CC BY-SA 4.0
2022-02-15T09:50:01.050Z
2022-02-15T09:50:01.050Z
Mark Morgan Lloyd
<p>I asked a question about transparencies, and while doing research for it, I found a lot of websites mentioned their products were <strong>N mil</strong> thickness.</p>
<p><strong>What does <em>mil</em> mean when talking about the thickness of a material? How does it compare to other common units of measure?</strong></p>

CC BY-SA 4.0
2022-02-15T09:50:18.767Z
As Sned at Cornell used to say: "A mil is a measure of angle." see: https://en.wikipedia.org/wiki/Milliradian#Definitions_for_maps_and_artillery
D Duck
<paper><plastic><terminology><wire><transparency>
What does 'mil' mean when measuring thickness?
Wimateeka
# What does 'mil' mean when measuring thickness?

(Asked by: username_0 on 2022-02-14)

I asked a question about transparencies, and while doing research for it, I found a lot of websites mentioned their products were **N mil** thickness.

**What does *mil* mean when talking about the thickness of a material? How does it compare to other common units of measure?**

**Tags:** paper, plastic, terminology, wire, transparency

> **Comments:**
> **username_1**: As Sned at Cornell used to say: "A mil is a measure of angle." see: https://en.wikipedia.org/wiki/Milliradian#Definitions_for_maps_and_artillery  

---

## 3 answers

### Answer by username_0 on 2022-02-14. Score: 8 | Accepted answer

The internet has informed me one **mil** is a measurement that equals one-thousandth of an inch (0.001 inch) or 0.0254 mm. You can convert any length unit into mils via [Google's length unit conversion](https://www.google.com/search?q=google%20mil%20to%20inch) (*Google labels it **Thousandth of an inch** instead of **mil***).

Per the comments below, there are some British English applications where the term **thou** (short for thousands) is used instead of **mil**.

I also learned that to convert between **mil** and **gauge** one can take the number of mil and multiply by 100; thus a 2 mil thickness converts to 200 gauge ([according to ULine's website](https://www.uline.com/CustomerService/ULINE_FAQ_Ans?FAQ_ID=49)).

Explanation of **mil** I found from a helpful [plastic sheeting website](https://www.globalplasticsheeting.com/mil-thickness-compared-to-mm-millimeter-and-inches):

> **How does mil thickness compare to mm (millimeter) and inches? What does mil stand for in measurement?**
>
> Plastic sheeting is measured in mils. A mil is a measurement that equals one-thousandth of an inch, or 0.001 inch. One mil also equals 0.0254 mm (millimeter). Thus a mil is not the same thickness as a millimeter. The term "mil" is not an abbreviation but a unit of measure.The chart below gives you an idea of mils to millimeters to inches. An every day trash bag ranges between 1.2 mils and 1.7 mils. A much stronger trash bag that offers better tear resistance is between 3 mils and 6 mils. A credit card is around 30 mils thick while a common deck of playing cards including the box is approximately .75 inches thick or 750 mils.
>
> | mil | mm | inch | Item |
> | --- | --- | --- | --- |
> | 1 | 0.0254 | 0.001 |  |
> | 3 | 0.07619 | 0.003 |  |
> | 6 | 0.152399 | 0.006 |  |
> | 10 | 0.254 | 0.01 (1/64 in) |  |
> | 15 | 0.381 | 0.015 |  |
> | 20 | 0.508 | 0.02 |  |
> | 30 | 0.762 | 0.03 (1/32 in) | Credit card |
> | 60 | 1.524 | 0.06 (1/16 in) |  |
> | 100 | 2.54 | 0.1 (3/32 in) |  |

Additionally, the same website had some [helpful information for visualizing thickness in mils](https://www.globalplasticsheeting.com/thickness-of-plastic-sheeting):

> **Thickness of Plastic Sheeting**
>
> Plastic Sheeting [...] is rated with the term, "mil". [...] Most human hair is One-thousandth of inch, or 0.001 inch [or 1 mil]. The most common size in the thickness rating for plastic sheeting is 6 mil. This is 6-thousandths of an inch, or 0.006 inch. Generally, the thicker the plastic, the stronger it is. If it has string/scrim reinforcement, then the string within the plastic will give it added strength. Depending on the application, the composition of the plastic can play a big role regardless of the thickness. For example, additives added to the plastic such as the fire retardant (FR) additive may play a more significant role than the thickness of the plastic if the job requires FR plastic.
>
> *Note that the term " heavy gauge" plastic is not to be confused with "heavy mil" referring to heavy plastic sheeting. The term "gauge" refers to the thickness of metal. It really doesn't apply to plastic sheeting/ plastic sheets.*
>
> | Thickness of Plastic Sheeting | Common item for comparison |
> | --- | --- |
> | 75 mil | U.S. Nickel |
> | 60 mil | U.S. Penny |
> | 50 mil | U.S. Dime |
> | 10 mil | Business card |
> | 6 mil | white trash bag used in kitchens |
> | 4 mil | standard piece of paper |

> **Comments:**
> **username_2**: That is definitely news to me. In non-Imperial measurement countries, such as the one I live in, I have always used mil as millimetre, because we only use metric measurements for this sort of thing.  
> **username_3**: Mil ( 0.001 in.) very commonly used world wide when discussing corrosion amount or rates. Also thickness of protective coatings ( paint).  
> **username_4**: @username_2 hence 0.001" being called "thou" in British English. "Mil" as used here is essentially an Americanism  that has gone international in some uses  
> **username_5**: I totally agree with username_2; I thought mil was a different abbreviation for millimetre. Kind of makes sense though... If you base your unit of measurement on the length of 3 corns of barley and you want to derive a much smaller unit of measurement you "mill" them down  XD  
> **username_6**: @username_4 yet mil predates English usage in other languages like Spanish.  
> **username_4**: @username_6 it's straight from Latin so it's not really surprising; it's also the logical choice in metric /SI prefixes. I would put the onus on the people using archaic units to deal with the confusion. Here in the UK we use both metric and imperial, but our modern engineering is firmly metric  
> **username_6**: @username_4 so you are used to millimeters right?  A thousands of a meter. Mil predates Thou in English usage by almost 100 years. And English the klepto it is imported thou from Germanic while most SI units are latin in nature.  
> **username_4**: @username_6 Yes, I'm used to mm, and nearly all my measuring kit is metric-only.  Whitworth was apparently using "thou" before 1850 (though I can only find reference to "thousandths" in sources I have access to), and was one of the first to propose working in decimal inches.  He would have had the choice of Latinate or Germanic vocabulary to derive his terminology. "mil" from milliradian has several similar angular meanings as well.  
> **username_7**: It bugged me that the first table gives 10 mil, which is 10/1000th or 1/100th of an inch, equal to 1/64th of an inch, which is 0.015625 inches, or about 15 mils. But it's not a transcription error, so I have to wonder if it's an error in the source or whether it's really conventional wisdom in the USC system. As a side note for @username_6, most SI prefixes derive from Greek, with a handful from Latin, French, Spanish or Danish.  
> **username_4**: @username_7 it's an error in the table, I reckon a flawed attempt to give some approximate conversions.  All the fractional values are off - obviously as sums of powers of 1/2 can't represent powers of 1/10 precisely - but some by more than others. The one you spotted is too far off to be a convenient approximation given that 15 mil (0.381mm) is listed and 1/64" is 0.397mm.  I do just enough with US-built kit to have a table of decimal inches, fractional inches, and mm on the wall next to my desk here in work.  
> **username_4**: Also *The term "mil" is not an abbreviation but a unit of measure* from the source is wrong.  At best they could say "no longer an abbreviation" but the full form "milli-inches" is often seen in old documents  
> **username_8**: 3 mil is the thickness of a heavy-duty "contractor" trash bag, not regular white kitchen bags. In case you want another couple reference points, I have 0.31 mil plastic sheeting to cover windows while painting; it's light and crinkly, flimsier than a grocery sack. 6 mil is one of the heaviest I've commonly found in big-box hardware stores (I used it to seal off lead abatement work).  
> **username_9**: Mil are *never* used as short version for milimeters in my experience (in speech, yes, written, never), but you'll see it a lot in printed circuit board (PCB) design. Many measurements on a PCB are in mil.  

---

### Answer by username_6 on 2022-02-15. Score: 1

This is basic English etymology:

> mil (n.)

> 1721, in per mil "per thousand," from Latin mille "thousand" (see million); compare percent. As a unit of length for diameter of wire (equal to .001 of an inch) it is attested from 1891; as a unit of angular measure it is recorded by 1907. <https://www.etymonline.com/word/mil>

Like a large part of English and typical imperial units, mil comes from Latin for thousands. ***As in One Thousands of an inch.*** Mil is also the root word for million. And milli as in milliamps or millimeters, in metric units. Mil is a the root of them all.

This is also true for other languages like Spanish, where a mil pesos for example means a thousand as in One Thousand Dollars.


---

### Answer by username_10 on 2022-02-15. Score: 0

"mil" is not a standardised unit, and whilst it can usually be interpreted as "one thousandth" of something the only safe course of action is to ask the supplier for clarification.

Having said that, it's *probably* safe to interpret it by context (e.g. paper would be unlikely to be several millimetres thick) and by reference to the location of the seller (Americans use English units, just about everybody else uses metric units). But you'd be most unwise to rely on that if gross misjudgement would be expensive: a court would probably not consider "I assumed that..." to be an adequate level of certainty.

> **Comments:**
> **username_9**: This answer is wrong. In certain industries, mil is used as a standardised unit. Perhaps not SI standardised, but in those sectors (like electronics R&D) it's very standard. 0.001".  
> **username_10**: @username_9 There are certain environments in which "Furlongs per Fortnight" and measuring lengths by comparing them with that of a London bus are popularly accepted. Quoting a length in mil has no more standing than that.  

---

