  The long term scaling prospects for solid-state quantum computing
architectures relies heavily on the ability to simply and reliably measure and
control the coherent electron interaction strength, known as the tunnel
coupling, $t_c$. Here, we describe a method to extract the $t_c$ between two
quantum dots (QDs) utilising their different tunnel rates to a reservoir. We
demonstrate the technique on a few donor triple QD tunnel coupled to a nearby
single-electron transistor (SET) in silicon. The device was patterned using
scanning tunneling microscopy-hydrogen lithography allowing for a direct
measurement of the tunnel coupling for a given inter-dot distance. We extract
${t}_{{\rm{c}}}=5.5\pm 1.8\;{\rm{GHz}}$ and ${t}_{{\rm{c}}}=2.2\pm
1.3\;{\rm{GHz}}$ between each of the nearest-neighbour QDs which are separated
by 14.5 nm and 14.0 nm, respectively. The technique allows for an accurate
measurement of $t_c$ for nanoscale devices even when it is smaller than the
electron temperature and is an ideal characterisation tool for multi-dot
systems with a charge sensor.
