Four miles is exactly 6.437376 kilometers

Four miles is 6.437376 kilometers. One international mile is 1,609.344 meters, a value fixed by the 1959 agreement and printed in NIST Special Publication 811, Appendix B.9. Multiply by four and the meters come to 6,437.376, the kilometers to 6.437376.

The mile is 5,280 feet, and a foot is 0.3048 m exactly, so 5,280 x 0.3048 = 1,609.344 m. No survey foot, no local variation, no rounding. The FHWA highway performance data handbook prints the same factor, 1 mile = 1.609344 kilometers, for converting its road records, which is why every state DOT file agrees with every running app.

The last two rows are the race distances. A half marathon is 13.1094 miles, which is 21.0975 km, and a marathon is 26.2188 miles, which is 42.195 km. Four miles is 30.5 percent of a half marathon and 15.2 percent of a marathon, so a four mile run is a short training day for anyone entered in either.

The 1.6 shortcut costs 37 meters at four miles

Most people multiply miles by 1.6 and stop there. At four miles that gives 6.4 km, while the exact answer is 6.437376 km, so the shortcut is 0.037376 km short, which is 37.376 meters. The error is 9.344 meters per mile and it grows in a straight line.

Thirty seven meters is 41 yards, about a third of a lap of a 400 meter track. On a walk to the store that is nothing. On a race it matters: a runner who trusts 6.4 km for a four mile split is 37 meters behind the true mark, which is 12.5 seconds at a 9 minute mile pace.

A better mental factor is 1.61. It gives 6.44 km at four miles, which is 2.6 meters long, and it holds up to about 20 miles before the error passes 20 meters. The exact factor is 1.609344, and 1.61 is close enough for a road sign, a fuel estimate or a training log.

A 9 minute mile is a 5:36 kilometer

Pace per kilometer is pace per mile divided by 1.609344, because a kilometer is the shorter unit and the same speed covers it sooner. Nine minutes is 540 seconds, and 540 / 1.609344 = 335.5 seconds, which is 5 minutes 35.5 seconds. Rounded to the second it reads 5:36 per kilometer.

Speed runs the other way. Covering 1,609.344 meters in 540 seconds is 2.98 meters per second, which is 10.73 km/h or 6.67 mph. A treadmill set to 10.7 km/h matches a 9 minute mile, and one set to 6.7 mph matches the same effort in the other unit.

A four mile run at 9:00 per mile takes 36 minutes. The same run in metric is 6.44 km at 5:36 per km, which also comes to 36 minutes. Split times are where the conversion earns its keep: a 5K split of 28:00 is 9:01 per mile, and a four mile race is 1.437376 km longer than a 5K.

Walking, running and driving four miles

Time is distance divided by speed, and the unit of the answer follows the unit you feed in. Four miles at 3 mph is 1 hour 20 minutes. Four miles at 65 mph is 3 minutes 42 seconds. Both cover the same 6.437376 km, and a metric driver holding 105 km/h covers it in the same 3 minutes 42 seconds.

The km/h column is the mph figure times 1.609344, the one conversion worth memorising for driving. 65 mph is 104.61 km/h, 70 mph is 112.65 km/h, and 25 mph, a school zone speed in many states, is 40.23 km/h. A Canadian sign reading 100 km/h is 62.14 mph, close to the 65 mph limit on the US side of the same highway.

Walking keeps the numbers friendly. An average adult walks about 3 mph, so four miles takes 80 minutes, and a brisk 4 mph walk covers it in exactly an hour. A run at 6 mph, which is a 10 minute mile, takes 40 minutes.

Four miles on a track, a treadmill and a step counter

A standard outdoor track is 400 meters per lap, so four miles is 16.09 laps: 6,437.376 / 400 = 16.09344. Run in lane one and that is 16 laps plus 37.4 meters. Most older US tracks measure 440 yards, which is 0.25 mile, and 16 laps of a 440 yard track is exactly four miles.

A treadmill in a metric gym shows 6.4 km for the same run, because the display rounds to one decimal. The gap is 37 meters, the same 1.6 shortcut error. Set the machine to 6.44 if it takes two decimals, or accept the 37 meter shortfall on a 36 minute run.

Step counters work from stride length. At the common estimate of 2,000 steps per mile, four miles is 8,000 steps. At 2,500 steps per mile, which suits a shorter stride, it is 10,000 steps. That is why a 10,000 step daily target is about 5 miles for one person and about 4 miles for another, with the same number on the wrist.

Road signs: miles at home, kilometers almost everywhere else

The United States and the United Kingdom are the two large countries that still sign road distances in miles. Everywhere else the sign is in kilometers, so a four mile leg of a trip becomes 6.4 km once you cross into Canada or Mexico. A drive from Detroit to Windsor changes units at the bridge.

Britain is the odd case. Distances and speed limits are in miles per hour, and gov.uk lists the national speed limits as 30 mph, 60 mph and 70 mph, with the metric figure alongside at 48, 96 and 112 km/h. Fuel there is sold by the litre, so a British driver converts distance one way and volume the other on the same fill up.

Water and air use a different mile. A nautical mile is 1,852 meters exactly, which is 1.15078 statute miles, or 15.1 percent longer than the mile on a road sign, so four nautical miles is 7.408 km and four statute miles is 3.4759 nautical miles. Knots follow from that: one knot is one nautical mile per hour, or 1.852 km/h, and a boat at 20 knots covers 37.04 km in an hour. A flight plan filed in nautical miles and a rental car odometer in miles are not measuring the same thing.

Four miles in meters, feet, yards and inches

The kilometer is the headline, and the smaller units are plain multiples of the mile. Four miles is 6,437.376 meters, 21,120 feet, 7,040 yards, 253,440 inches and 6,437,376 millimeters. Every one of them comes from the same 1,609.344 m mile, so none of them can disagree with the others.

The 5K row is the one runners use. A 5K is 3.10686 miles, so four miles is 1.437376 km longer, and a four mile race takes about 29 percent longer than a 5K at the same pace. A 10K is 6.21371 miles, so four miles falls 3.562624 km short of it. Both gaps are worth knowing before you enter a race in a country that signs everything in kilometers.

Rounding four miles for a log, a chart or a sentence

One decimal, 6.4 km, is 37.376 meters short. Two decimals, 6.44 km, is 2.624 meters long. Three decimals, 6.437 km, is 0.376 meters short. Four decimals, 6.4374 km, is 24 millimeters long. Any of them is fine for a blog post, and only the last two are fine for a race split.

The right choice depends on what the number is for. A fuel estimate at 30 mpg over four miles uses 0.133 gallons, and a 1 percent error in distance moves that by 0.0013 gallons, so one decimal is plenty. A training log that compares weeks needs two decimals, because 0.04 km a run adds up to 2 km over 50 runs.

Write the unit every time. A bare 6.4 in a running log could be miles or kilometers, and the difference between the two readings is 3.9 km. The safe habit is to keep miles in the source column and kilometers in a derived column, which is how the tables above are built and how every race app stores its data.