Whether you are reading a race report from a European tour, comparing notes with a riding buddy across the Atlantic, or simply trying to make sense of a speed limit sign while bikepacking abroad, sooner or later you will need to switch between miles per hour and kilometres per hour. The conversion itself is fixed and simple, but cyclists have their own quirks around it: bike computers and phones display speed differently, average and maximum speeds tell very different stories, and "fast" means something different for a commuter than for a racer. This guide gives you the exact factors, quick mental maths, a reference table, and the context to interpret any speed you see.

The conversion factor

There are two numbers to remember, and they are exact:

  • 1 mph = 1.60934 km/h
  • 1 km/h = 0.621371 mph

So to go from miles per hour to kilometres per hour, multiply by 1.60934; to go the other way, multiply by 0.621371 (or equivalently, divide by 1.60934). A 20 mph effort is 20 × 1.60934 = 32.2 km/h. A 30 km/h pace is 30 × 0.621371 = 18.6 mph. These two factors are reciprocals of each other, which is why one is a bit above 1.6 and the other a bit above 0.6.

Quick mental maths

You rarely need three decimal places in the saddle, so here are shortcuts that get you within a fraction of a unit:

  • mph → km/h: multiply by 1.6. For a sharper figure, add 5%: 20 mph → 32, plus a touch → ~32.2. Or use 8/5 — multiply by 8 and divide by 5 (20 × 8 = 160, ÷ 5 = 32).
  • km/h → mph: multiply by 0.6 and nudge up slightly, or use 5/8 — multiply by 5 and divide by 8 (32 × 5 = 160, ÷ 8 = 20).
  • The handy anchor: 25 km/h ≈ 15.5 mph, and 16 km/h ≈ 10 mph. Many riders memorise one anchor and scale from it.

For anything where precision matters — pacing to a target average, or logging a ride — use the mph↔km/h converter on the Convert.bike home page rather than rounding in your head.

Reference table of common cycling speeds

These are the speeds cyclists quote most often, converted both ways and rounded to one decimal place.

  • 15 km/h = 9.3 mph
  • 20 km/h = 12.4 mph
  • 25 km/h = 15.5 mph
  • 30 km/h = 18.6 mph
  • 35 km/h = 21.7 mph
  • 40 km/h = 24.9 mph
  • 10 mph = 16.1 km/h
  • 15 mph = 24.1 km/h
  • 20 mph = 32.2 km/h
  • 25 mph = 40.2 km/h
  • 30 mph = 48.3 km/h

Notice that 25 mph and 40 km/h are almost the same speed — a useful coincidence worth memorising, since both crop up as reference points in different countries.

What counts as fast? Typical speeds by riding type

Raw numbers mean little without context. Here is roughly what different riders sustain as an average over a ride, on reasonable terrain:

  • Relaxed commuting / leisure: around 15-20 km/h (9-12 mph). Comfortable, conversational, in everyday clothes.
  • Brisk commuting / fit rider: 20-28 km/h (12-17 mph).
  • Loaded touring: 18-24 km/h (11-15 mph) — heavy bags and long days keep averages modest.
  • Road cycling, recreational to keen: 25-32 km/h (15-20 mph) solo on the flat; faster in a group thanks to drafting.
  • Strong club / racing pace: 32-40+ km/h (20-25+ mph), often only sustainable in a bunch.
  • E-bikes: typically cruise at 25 km/h (15.5 mph), because that is where most legal pedal-assist systems cut their motor support.

That e-bike figure is not a coincidence: in the EU and UK, legal pedal-assist (EAPC) e-bikes stop adding power at 25 km/h, while the common US pedelec limit is 20 mph (32 km/h) for class 1 and 2. If you are converting or considering a conversion, those legal speed caps are central — our complete guide to converting a bike to electric covers the limits and what they mean for your build in detail.

How bike computers and GPS show units

Almost every cycling computer, GPS head unit and phone app can display speed in either mph or km/h — the data is the same, only the label changes. The unit is set in the device's settings, usually under "units", "measurement system" or by choosing statute (miles) versus metric (kilometres).

  • Dedicated computers (wheel-magnet type): set the units and, critically, program in the correct wheel circumference, or every reading will be off regardless of units. See our wheel-size guide to find the right figure.
  • GPS units and phone apps: derive speed from satellite position, so there is no wheel size to set, but you still choose mph or km/h in settings. Switching units never changes your recorded ride — it just relabels it.

If your numbers ever look implausible, check the units first; a ride that suddenly reads 1.6 times faster has simply flipped from mph to km/h.

Keeping units consistent when you travel and share

A surprising amount of confusion comes not from a wrong calculation but from mixed units. If you ride mostly in the UK or US you probably think in miles, yet most of the cycling world — including pro racing, European sportives and the great majority of training data shared online — works in kilometres. When you upload a ride to a sharing platform, the figures are stored as raw data and simply displayed in whatever unit your account prefers, so two people looking at the exact same ride can see 30 km/h and 18.6 mph and briefly believe they rode differently. Before you compare a Strava segment, a club ride average or a published race speed against your own, glance at the unit label. A single conversion sorts it out; an unnoticed mismatch can have you chasing a target that is really 1.6 times harder or easier than you thought.

Average versus maximum speed

One of the most common sources of confusion is comparing the wrong numbers. Maximum speed is the single fastest instant of your ride — almost always hit on a descent, and easily inflated by GPS noise or a brief downhill tuck. Average speed is total distance divided by total time, and it absorbs every climb, junction, headwind and coffee stop.

The two can be wildly different: a ride averaging 24 km/h (15 mph) might have a max of 60 km/h (37 mph) from one long descent. That is why average speed is the honest measure of your overall pace and fitness, while max speed is mostly a fun statistic. Many computers also offer "moving average", which pauses the clock when you stop — a moving average will read higher than the overall average on a stop-start commute. When comparing rides or riders, make sure you are comparing like with like: average to average, in the same units.

Speed also ties directly into your gearing and cadence. The speed you can hold depends on the gear you turn and how fast you spin it, which our bike speed, cadence and gearing calculator lets you explore, and which connects to the broader topic of gear inches and development.

Why the same effort gives different speeds

Once you start comparing converted speeds, it helps to know why two riders putting out identical effort can post very different numbers — it stops you reading too much into a single figure. The biggest factor is air resistance, which rises steeply with speed: at 30 km/h the vast majority of your effort goes into pushing air aside, so a modest headwind or an upright position can cost several km/h. Drafting behind another rider can save a large slice of that, which is exactly why bunch averages dwarf solo ones. Terrain matters just as much; a hilly route will show a far lower average than a flat one for the same legs, because the time lost grinding uphill is never fully recovered on the descent. Road surface, tyre choice and pressure, total weight, and even temperature all nudge the number too. The practical lesson is to convert and compare speeds only between genuinely similar rides. A 28 km/h (17.4 mph) solo average into a headwind on rolling roads may represent more work than a 34 km/h (21.1 mph) average sitting in a fast group on the flat — the raw figures, in either unit, do not tell that story on their own.

Next steps

Commit the two factors to memory — 1.60934 and 0.621371 — and pick one mental shortcut (the 8/5 and 5/8 trick works well) for on-the-bike estimates. Set your computer or app to whichever unit you think in, and double-check the wheel circumference if it uses a magnet sensor. When accuracy counts, run the figure through the home-page mph↔km/h converter rather than rounding. And next time you log a ride, look past the headline max speed to your average, in consistent units — that is the number that actually tracks your progress. From there, dig into how gearing shapes the speeds you can hold with our speed and gearing calculator.