KM/H vs MPH: Quick Reference for Drivers and Cyclists
A practical guide to comparing speed displays in km/h and mph without confusing units or over-trusting a phone reading.
Kilometres per hour and miles per hour are both units of speed, but their numeric values differ. The same movement produces a larger number in km/h than in mph. A unit mismatch is one of the simplest explanations for a speed tracker appearing to disagree with a dashboard, bike computer or fitness device.
A simple mental reference
For a rough mental conversion, 5 mph is about 8 km/h, 20 mph is about 32 km/h, and 60 mph is about 97 km/h. For the reverse direction, 30 km/h is about 19 mph and 100 km/h is about 62 mph. These rounded references are useful for quick understanding, not for enforcing speed limits or calibrating equipment.
Compare like with like
Before comparing two displays, confirm that both show the same unit and the same kind of speed. One may show instantaneous speed while another smooths readings over several seconds. A bicycle computer may use a wheel sensor, whereas a phone may use location estimates. Unit agreement is necessary but not sufficient for a fair comparison.
Avoid risky testing
Do not ask a driver to read or adjust a phone while moving. If a comparison is necessary, a passenger can observe the display on a lawful route, or the device can be checked while stationary. A phone-based tracker is not a replacement for the vehicle's approved speedometer and should never be used to justify exceeding a posted limit.
If the numbers still disagree
Repeat the comparison only when both readings are stable and the route has a clear view of the sky. Record the unit, conditions and approximate time. If the difference is inconsistent, the issue may be GPS noise, sensor lag, device placement or display smoothing rather than a conversion error.
Frequently asked questions
Is 100 km/h the same as 100 mph?
No. 100 km/h is about 62 mph; 100 mph is about 161 km/h.
Which unit should I use?
Choose the unit you understand and that matches the signs or equipment relevant to your location.
Technical references
These references explain the underlying browser and positioning concepts. They do not imply endorsement of this website.