km/h, mph or Knots — Which Speed Unit Should You Use

Speedometer displays the same measurement in three units. Choosing between them is not a technical decision — it is a question of which number you can interpret without thinking.

The conversions

The mental shortcut for km/h to mph: halve it, then add a tenth of the half. 100 km/h → 50 + 5 = 55 mph. The true value is 62, so that shortcut under-reads; the better one is to take 60 percent and add a little. In practice, if you need the conversion often enough to want a trick, switch the unit in the app instead.

Where each unit belongs

km/h is the road unit almost everywhere: continental Europe, Türkiye, most of Asia, Africa, South America, Canada and Australia. If your speed limit signs show 50, 90 and 120, this is your unit.

mph is used on roads in the United States and the United Kingdom, plus a handful of other jurisdictions. Limits appear as 30, 60, 70.

knots belongs to boats and aircraft. One knot is one nautical mile per hour, and a nautical mile is one minute of latitude — which is why the unit survives: it maps directly onto navigation charts. On a car journey it is a curiosity; on the water it is the only unit anyone will understand.

Accuracy does not change

This is worth being explicit about, because the question comes up. The receiver calculates your velocity once, in metres per second, from satellite signals. Everything you see is that value formatted. Switching from km/h to mph does not add or remove error; it only moves the decimal point and relabels the number.

What does change is granularity of judgement. At motorway speed, 1 mph is 1.6 km/h — so a display in mph moves in coarser real-world steps. Neither is better; they are just different resolutions on the same underlying figure.

Match the gauge scale to the unit

If you use the analog face, the scale setting matters more than the unit itself. A dial that runs to 0–210 is well proportioned for km/h road driving: town speeds sit low, motorway speeds sit in the upper middle, and the needle sweeps a satisfying arc.

Put mph on the same 0–210 dial and every road speed you will ever see crowds into the first third. The needle barely moves, and the whole advantage of an analog face — reading position rather than digits — disappears. Drop the scale so the speeds you actually drive occupy the middle of the sweep.

The same logic applies to cycling. If you never exceed 40 km/h, a 210 scale wastes 80 percent of the dial; a lower scale turns the same instrument into something you can read from the corner of your eye.

Changing it

Both settings live in the profile tab: the unit selector at the top (KMH, MPH, KNOTS) and the scale below it, alongside transport type and the speed limit threshold. The change applies immediately to all three display faces and to new trips; trips already recorded keep the figures they were saved with.