Thrust-to-weight ratio is a ratio of thrust to weight of a rocket, jet engine, propeller engine, or a vehicle propelled by such an engine. It is a dimensionless quantity and is an indicator of the performance of the engine or vehicle.
The instantaneous thrust-to-weight ratio of a vehicle varies continually during operation due to progressive consumption of fuel or propellant, and in some cases due to a gravity gradient. The thrust-to-weight ratio based on initial thrust and weight is often published and used as a figure of merit for quantitative comparison of the initial performance of vehicles.
The thrust-to-weight ratio can be calculated by dividing the thrust (in SI units – in newtons) by the weight (in newtons) of the engine or vehicle. It is a dimensionless quantity.
For valid comparison of the initial thrust-to-weight ratio of two or more engines or vehicles, thrust must be measured under controlled conditions.
The thrust-to-weight ratio and wing loading are the two most important parameters in determining the performance of an aircraft. For example, the thrust-to-weight ratio of a combat aircraft is a good indicator of the manoeuvrability of the aircraft.
The thrust-to-weight ratio varies continually during a flight. Thrust varies with throttle setting, airspeed, altitude and air temperature. Weight varies with fuel burn and changes of payload. For aircraft, the quoted thrust-to-weight ratio is often the maximum static thrust at sea-level divided by the maximum takeoff weight.
Propeller-driven aircraft 
For propeller-driven aircraft, the thrust-to-weight ratio can be calculated as follows:
- is engine power
The thrust-to-weight ratio of a rocket, or rocket-propelled vehicle, is an indicator of its acceleration expressed in multiples of gravitational acceleration g.
Rockets and rocket-propelled vehicles operate in a wide range of gravitational environments, including the weightless environment. It is customary to calculate the thrust-to-weight ratio using initial gross weight at sea-level on earth. This is sometimes called Thrust-to-Earth-weight ratio. The thrust-to-Earth-weight ratio of a rocket, or rocket-propelled vehicle, is an indicator of its acceleration expressed in multiples of earth’s gravitational acceleration, g0.
It is important to note that the thrust-to-weight ratio for a rocket varies as the propellant gets utilized. If the thrust is constant, then the maximum ratio (maximum acceleration of the vehicle) is achieved just before the propellant is fully consumed (propellant weight is practically zero at this point). So for each rocket there a characteristic thrust-to-weight curve or acceleration curve, not just a scalar quantity.
The thrust-to-weight ratio of an engine is larger for the bare engine than for the whole launch vehicle. The thrust-to-weight ratio of a bare engine is of use since it determines the maximum acceleration that any vehicle using that engine could theoretically achieve with minimum propellant and structure attached.
For a takeoff from the surface of the earth using thrust and no aerodynamic lift, the thrust-to-weight ratio for the whole vehicle has to be more than one. In general, the thrust-to-weight ratio is numerically equal to the g-force that the vehicle can generate. Provided the vehicle's g-force exceeds local gravity (expressed as a multiple of g0) then takeoff can occur.
The thrust to weight ratio of rockets is typically far higher than that of airbreathing jet engines. This is because of the much higher density of the material that is formed into the exhaust, compared to that of air; therefore, far less engineering materials are needed for pressurising it.
Many factors affect a thrust-to-weight ratio, and the instantaneous value typically varies over the flight with the variations of thrust due to speed and altitude, and the weight due to the remaining propellant and payload mass. The main factors that affect thrust include freestream air temperature, pressure, density, and composition. Depending on the engine or vehicle under consideration, the actual performance will often be affected by buoyancy and local gravitational field strength.
The Russian-made RD-180 rocket engine (which powers Lockheed Martin’s Atlas V) produces 3,820 kN of sea-level thrust and has a dry mass of 5,307 kg. Using the Earth surface gravitational field strength of 9.807 m/s², the sea-level thrust-to-weight ratio is computed as follows: (1 kN = 1000 N = 1000 kg⋅m/s²)
|Concorde||0.373||Max Takeoff Weight, Full Reheat|
|English Electric Lightning||0.63||maximum takeoff weight, No Reheat|
|F-22 Raptor||>1.09 (1.26 with loaded weight & 50% fuel)||Maximum takeoff weight, Dry Thrust|
|Mikoyan MiG-29||1.09||Full internal fuel, 4 AAMs|
|F-15 Eagle||1.04||nominally loaded|
|F-16 Fighting Falcon||1.096|
|Hawker Siddeley Harrier||1.1|
|English Electric Lightning||~1.2||on an empty weight basis, full reheat|
|Eurofighter Typhoon||1.07 (100% fuel, 2 IRIS-T, 4 MBDA Meteor)|
|Space Shuttle||1.5||Take-off |
|Dassault Rafale||0.988 (100% fuel, 2 EM A2A missile, 2 IR A2A missile) version M |
|Space Shuttle||3||Peak (throttled back for astronaut comfort)|
Jet and Rocket Engines 
|Jet or Rocket engine||Mass
|RD-0410 nuclear rocket engine||2,000||4,400||35.2||7,900||1.8|
|J58 jet engine (SR-71 Blackbird)||2,722||6,000||150||34,000||5.2|
|Rolls-Royce/Snecma Olympus 593
turbojet with reheat (Concorde)
|Pratt & Whitney F119||1,800||3,900||91||20,500||7.95|
|RD-0750 rocket engine, three-propellant mode||4,621||10,190||1,413||318,000||31.2|
|RD-0146 rocket engine||260||570||98||22,000||38.4|
|SSME rocket engine (Space Shuttle)||3,177||7,000||2,278||512,000||73.1|
|RD-180 rocket engine||5,393||11,890||4,152||933,000||78.5|
|F-1 (Saturn V first stage)||8,391||18,500||7,740.5||1,740,100||94.1|
|NK-33 rocket engine||1,222||2,690||1,638||368,000||136.7|
|Merlin 1D rocket engine||440||970||690||160,000||159.9|
Rocket thrusts are vacuum thrusts unless otherwise noted
Fighter Aircraft 
Table a: Thrust To Weight Ratios, Fuels Weights, and Weights of Different Fighter Planes
|Specifications / Fighters||F-15K||F-15C||MiG-29K||MiG-29B||JF-17||J-10||F-35A||F-35B||F-35C||F-22|
|Engine(s) Thrust Maximum (lbf)||58,320 (2)||46,900 (2)||39,682 (2)||36,600 (2)||18,300 (1)||27,557 (1)||39,900 (1)||39,900 (1)||39,900 (1)||70,000 (2)|
|Aircraft Weight Empty (lb)||37,500||31,700||28,050||24,030||14,520||20,394||29,300||32,000||34,800||43,340|
|Aircraft Weight Full fuel (lb)||51,023||45,574||39,602||31,757||19,650||28,760||47,780||46,003||53,800||61,340|
|Aircraft Weight Max Take-off load (lb)||81,000||68,000||49,383||40,785||28,000||42,500||70,000||60,000||70,000||83,500|
|Total fuel weight (lb)||13,523||13,874||11,552||07,727||05,130||08,366||18,480||14,003||19,000||18,000|
|T/W ratio (Thrust / AC weight full fuel)||1.14||1.03||1.00||1.15||0.93||0.96||0.84||0.87||0.74||1.14|
Table b: Thrust To Weight Ratios, Fuels Weights, and Weights of Different Fighter Planes (In International System)
|In International System||F-15K||F-15C||MiG-29K||MiG-29B||JF-17||J-10||F-35A||F-35B||F-35C||F-22|
|Engine(s) Thrust Maximum (kgf)||26,456 (2)||21,274 (2)||18,000 (2)||16,600 (2)||08,300 (1)||12,500 (1)||18,098 (1)||18,098 (1)||18 098 (1)||31,764 (2)|
|Aircraft Weight Empty (kg)||17,010||14,379||12,723||10,900||06,586||09,250||13,290||14,515||15,785||19,673|
|Aircraft Weight Full fuel (kg)||23,143||20,671||17,963||14,405||08,886||13,044||21,672||20,867||24,403||27,836|
|Aircraft Weight Max Take-off load (kg)||36,741||30,845||22,400||18,500||12,700||19,277||31,752||27,216||31,752||37,869|
|Total fuel weight (kg)||06,133||06,292||05,240||03,505||02,300||03,794||08,382||06,352||08,618||08,163|
|T/W ratio (Thrust / AC weight full fuel)||1.14||1.03||1.00||1.15||0.93||0.96||0.84||0.87||0.74||1.14|
- Fuel density used in calculations = 0.803 Kilograms/Liter
- The Number inside ( ) brackets is the Number of Engine(s).
- Engines powering F-15K are the Pratt & Whitney Engines, not General Electric's.
- MiG-29K's empty weight is an estimate.
- JF-17's Engine rating is of RD-93.
- JF-17 if mated with its engine WS-13, and if that engine gets its promised 18,969 lb then the T/W ratio becomes 0.97
- J-10's empty weight & fuel weight is an estimate.
- J-10's Engine rating is of AL-31FN.
- J-10 if mated with its engine WS-10A, and if that engine gets its promised 132 KN(29,674 lbf) then the T/W ratio becomes 1.03
See also 
- John P. Fielding. Introduction to Aircraft Design, Cambridge University Press, ISBN 978-0-521-65722-8
- Daniel P. Raymer (1989). Aircraft Design: A Conceptual Approach, American Institute of Aeronautics and Astronautics, Inc., Washington, DC. ISBN 0-930403-51-7
- George P. Sutton & Oscar Biblarz. Rocket Propulsion Elements, Wiley, ISBN 978-0-471-32642-7
- Daniel P. Raymer, Aircraft Design: A Conceptual Approach, Section 5.1
- John P. Fielding, Introduction to Aircraft Design, Section 4.1.1 (p.37)
- John P. Fielding, Introduction to Aircraft Design, Section 3.1 (p.21)
- Daniel P. Raymer, Aircraft Design: A Conceptual Approach, Equation 5.2
- Daniel P. Raymer, Aircraft Design: A Conceptual Approach, Equation 5.1
- George P. Sutton & Oscar Biblarz, Rocket Propulsion Elements (p. 442, 7th edition) “thrust-to-weight ratio F/Wg is a dimensionless parameter that is identical to the acceleration of the rocket propulsion system (expressed in multiples of g0) if it could fly by itself in a gravity-free vacuum”
- George P. Sutton & Oscar Biblarz, Rocket Propulsion Elements (p. 442, 7th edition) “The loaded weight Wg is the sea-level initial gross weight of propellant and rocket propulsion system hardware.”
- "Thrust-to-Earth-weight ratio". The Internet Encyclopedia of Science. Retrieved 2009-02-22.
- "F-15 Eagle Aircraft". About.com:Inventors. Retrieved 2009-03-03.
- Section 9 "The English Electric (BAC) Lightning". Vectorsite. Archived from the original on 2004-02-04. Retrieved 2012-10-12.
- Kampflugzeugvergleichstabelle Mader/Janes
- Thrust: 6.781 million lbf, Weight: 4.5 million lb"Space Shuttle". Wikipedia. Retrieved 2009-09-10.
- "Space Shuttle". Wikipedia. Retrieved 2009-09-10.
- Wade, Mark. "RD-0410". Encyclopedia Astronautica. Retrieved 2009-09-25.
- "«Konstruktorskoe Buro Khimavtomatiky» - Scientific-Research Complex / RD0410. Nuclear Rocket Engine. Advanced launch vehicles". KBKhA - Chemical Automatics Design Bureau. Retrieved 2009-09-25.
- Aircraft: Lockheed SR-71A Blackbird
- "Factsheets : Pratt & Whitney J58 Turbojet". National Museum of the United States Air Force. Retrieved 2010-04-15.
- "Rolls-Royce SNECMA Olympus - Jane's Transport News". Retrieved 2009-09-25. "With afterburner, reverser and nozzle ... 3,175 kg ... Afterburner ... 169.2 kN"
- Military Jet Engine Acquisition, RAND, 2002.
- "«Konstruktorskoe Buro Khimavtomatiky» - Scientific-Research Complex / RD0750.". KBKhA - Chemical Automatics Design Bureau. Retrieved 2009-09-25.
- "RD-180". Retrieved 2009-09-25.
- Encyclopedia Astronautica: F-1
- Astronautix NK-33 entry
- "SpaceX Unveils Plans To Be World’s Top Rocket Maker". Aviation Week and Space Technology. 2011-08-11. Retrieved 2012-10-11.(subscription required)
- "Lockheed Martin Website".