Pace is speed upside down
Runners, cyclists and swimmers mostly do not talk about speed. They talk about pace — minutes per kilometre, or minutes per mile — and that is not another speed unit. It is the reciprocal: distance per time turned into time per distance.
The practical consequence is that pace and speed move in opposite directions. A faster runner has a lower pace number. 5:00 per km is quicker than 6:00 per km, while 12 km/h is quicker than 10 km/h. Anything that treats pace as a unit of speed and multiplies by a factor gets both the number and the direction wrong.
The conversion is a division rather than a multiplication. To turn a pace into a speed: 60 divided by the pace in minutes per kilometre gives km/h — so 5:00/km is 60 ÷ 5 = 12 km/h. Going the other way is the same division: 60 ÷ 12 = 5 minutes per kilometre. The minutes-and-seconds format adds one step, because 5:30 is 5.5 minutes, not 5.3.
This tool converts speeds, not paces, and says so rather than quietly offering a “min/km” option that would behave unlike every other unit in the list.
Why knots exist
A knot is one nautical mile per hour, and a nautical mile is exactly 1,852 metres — which looks like an arbitrary number until you see where it comes from. It approximates one minute of latitude. Sixty nautical miles is therefore about one degree of latitude, anywhere on Earth.
That is the whole reason the unit survives. On a marine or aeronautical chart, latitude is printed up the side, so a navigator can measure a distance directly off the chart’s own scale without converting anything. A speed in knots and a chart in degrees are the same system; a speed in km/h is not.
A knot is 1.852 km/h exactly and about 1.151 mph, so the rough mental conversion is to add a bit under a sixth. The word itself is a measurement method rather than a unit: sailors counted knots tied at intervals in a line paid out behind the ship over a timed interval, which is also why “knots per hour” is wrong — the per hour is already in the knot.
Reading a speed limit abroad
The United States and the United Kingdom post limits in mph; almost everywhere else posts in km/h. A sign reading 100 outside those two countries is 62 mph, not 100 mph — which is the direction that matters, because assuming mph makes the limit look higher than it is.
The conversions worth carrying: 30 km/h is 18.6 mph, 50 km/h is 31.1, 80 km/h is 49.7, 100 km/h is 62.1, and 130 km/h — the common European motorway limit — is 80.8 mph. Going the other way, 30 mph is 48.3 km/h, 60 mph is 96.6, and 70 mph is 112.7.
A workable mental rule for km/h to mph is to take half and add a tenth of the original: 100 → 50 + 10 = 60, against the true 62.1. It is a slight underestimate, which is the safe direction to be wrong in when reading a limit.
Speed, velocity and average speed
Three related quantities get used interchangeably and are not the same. Speed is how fast, with no direction. Velocity is speed with a direction attached, which is why a car going round a roundabout at a steady 30 km/h has constant speed and continuously changing velocity. Everything on this page is speed.
Average speed is total distance divided by total time, and it is not the average of the speeds along the way. Drive 60 km at 60 km/h and then 60 km at 20 km/h: the average of the two numbers is 40 km/h, but the journey took one hour plus three hours for 120 km, giving 30 km/h. The slow section takes more time, so it gets more weight.
That is the same pooling error as averaging a column of percentages, and it has the same fix: work from the totals, not from the averages.
Doing it in a spreadsheet
Speed is a compound unit, so CONVERT is fiddlier here than elsewhere. Writing the factor out is clearer: =A1*1.609344 for mph to km/h, =A1/1.609344 back, =A1*1.852 for knots to km/h, and =A1*3.6 for m/s to km/h — all exact.
For pace, the useful pair is =60/A1 to turn minutes per kilometre into km/h and the identical =60/A1 to go back, since a reciprocal is its own inverse. To read a mm:ss pace typed as text, =MINUTE(A1)+SECOND(A1)/60 gives decimal minutes first — the step that gets skipped when 5:30 is entered as 5.3.
Sources and methodology
Nothing here is fetched and there is no data feed: every figure is computed from what you type. The factors are exact because their components are — the statute mile from the 1959 inch, the nautical mile as an exact 1 852 m — and the sources settle those definitions plus the aviation convention that keeps knots in use.