Length Converter

Length is the most familiar measurement there is, which is exactly why the tangle of units around it causes so much grief. This converter uses the meter as its base and bridges the metric and imperial systems.

Metric:

• 1 meter = 1,000 mm = 100 cm = 0.001 km

Imperial:

• 1 meter = 39.3701 inches = 3.28084 feet = 1.09361 yards

Cross-system (exact):

• 1 inch = 2.54 cm
• 1 foot = 0.3048 m
• 1 yard = 0.9144 m
• 1 mile = 1.60934 km

For scale:

• A doorway: about 2 m (6.6 ft)
• A football field: 100 yards (91.44 m)
• A marathon: 42.195 km (26.219 miles)

The reason metric feels easier is that everything scales by powers of ten, so moving from millimeters to meters to kilometers is just sliding a decimal point. The imperial system carries a different multiplier at every step: 12 inches to a foot, 3 feet to a yard, 1,760 yards to a mile. There’s history behind each one, but no pattern to lean on.

The inch-to-centimeter relationship is the one worth memorizing, because it’s exact: 1 inch is precisely 2.54 cm, fixed by international agreement in 1959. Most cross-system conversions are rounded, but that one isn’t, which makes it the safest pivot when you’re moving a measurement between systems by hand.

In fact every imperial figure in the list above is exact, not rounded, once you trace it back to that 1959 agreement. A foot is defined as 0.3048 m, a yard as 0.9144 m, and a mile as 1,609.344 m, all by definition rather than by measurement. The awkward-looking decimals in the other direction (39.3701 inches to a meter) are the rounded ones, because they are the reciprocals.

Reading a decimal foot is where people trip. A calculator that says 5.75 feet does not mean 5 feet 75 inches, and it does not mean 5 feet 7 inches either. Multiply the decimal part by 12: 0.75 x 12 = 9, so it is 5 feet 9 inches. Get this backwards and you are off by a couple of inches, which on a door frame or a curtain drop is the difference between fitting and not. The converter above prints the feet-and-inches form alongside the decimal so there is nothing to work out.

One more trap worth naming: the US survey foot. Until it was retired at the end of 2022 it was very slightly longer than the international foot, by about two parts per million. Irrelevant on a tape measure and quite relevant across a county, which is why old land surveys and state plane coordinates can disagree with modern GPS by a few feet over long distances. Everything on this page uses the international foot.