Travel Time (mph and km/h)

Travel time from distance and speed

Time equals distance over speed: t = d / v. The one thing to watch is that the units match. The U.S., the UK and a handful of other countries measure in miles per hour (mph), while the rest of the world runs on km/h. To convert, 1 mph = 1.609 km/h and 1 km/h = 0.6214 mph. Example: São Paulo to Rio de Janeiro is 430 km; hold an average of 100 km/h and the trip works out to 430/100 = 4.30 h ≈ 4 h 18 min.

Applications

It comes in handy for international travel, where you can read U.S. speed limits and ETAs in mph without second-guessing yourself. Planning a U.S. road trip? The map gives you miles and the speedometer gives you km/h, so a quick conversion keeps both honest. It also covers race pace and ETAs on bike GPS units like the Garmin Edge or Wahoo, which let you flip between mph and km/h. Keep in mind that real average speed always lands below cruise speed once you factor in refueling, tolls, traffic and breaks, so for highway estimates I'd plan around 80–90% of cruise.

FAQ

How do I convert mph to km/h quickly? Multiply by 1.609, so 60 mph comes out to about 96.6 km/h.

How do I write 4.30 h as h and min? Multiply the decimal part: 0.30 × 60 = 18 min, which makes 4.30 h the same as 4 h 18 min. Watch out, the 0.30 is not 30 minutes.

Why is my actual time longer than calculated? Because the formula assumes you hold one speed the whole way. On long trips, pad the result by 10–20% to cover stops, traffic and toll plazas.

How do I find average speed from time? Flip the formula around: v = d / t. Cover 430 km in 5 h and your average was 86 km/h.