Convert m to yd

The metre has been defined since 1983 as the distance light travels in 1/299,792,458 of a second. It is not a physical object any more; the platinum bar in Paris was retired.

A yard is three feet, and outside American football and fabric shops it is a unit most people rarely meet. It is defined as exactly 0.9144 metres.

The factor is 1.093613, and almost nobody carries that around. Rounded to 1.09 it is off by 0.33 % — which stays invisible on small numbers and turns into a whole unit somewhere around 1,000 m.

That is the number worth knowing before you round: not the error itself, but where it stops being ignorable. Below that point the shorter factor is the sensible one; above it, use the field above, which never rounds until it prints.

The yard has been defined in metric terms since the international yard and pound agreement of 1959, and in this page's units that comes out at 0.9144 m to one. The definition is exact by stipulation — it was not measured, and it cannot be refined by measuring it better. The decimal above is the whole of it, with nothing rounded away at the end.

Before that agreement the US and the British versions differed slightly, and old survey figures still carry the older definition. For anything outside land surveying the difference is far below the precision anybody is working to.

The gap is 8.56 cm, which is small enough to be invisible on a single length and large enough to accumulate into a real distance. Over a hundred units it is 8.56 m; over a golf hole of 400 it is 34 m; over a marathon's worth it is nearly four kilometres. The reason this pair confuses people is precisely that the two units are close: nothing looks obviously wrong until the numbers are added up.

Watch the direction of the percentage. A metre is 9.36 per cent longer than a yard, but a yard is only 8.56 per cent shorter than a metre, because the two figures are taken against different baselines. Adding ten per cent to convert metres to yards and then taking ten per cent off to come back does not return you to where you started, and over a long distance the round trip loses about one per cent.

American collegiate and high school swimming is contested in 25-yard pools, which are 22.86 m long. A 100-yard race is therefore 91.44 m, and a 200-yard race 182.88 — eight and a half and seventeen metres short of their metric namesakes. The distance difference alone would make yard times faster; the extra turns in a shorter pool make them faster again, because a push-off is quicker than swimming.

This is why swimming keeps three separate sets of records — short course yards, short course metres and long course metres — rather than one set with conversions. Governing bodies do publish factors for seeding across course types, and they are empirical rather than geometric: they are derived from what swimmers actually do, not from the ratio 0.9144, because the turns are not proportional to the distance.

Athletics tracks in Britain and the United States were built to a quarter mile — 440 yards, or 402.336 m. When the sport standardised on 400 m the tracks were rebuilt or remarked, and the races changed length rather than changing name: a 440 was 2.34 m longer than the 400 that replaced it, and a 220 was 1.17 m longer than a 200.

That difference is small and it was not treated as small, because sprint records live in hundredths. Rather than convert imperial marks into metric ones, the governing bodies retired them and started the metric lists fresh. The mile is the one imperial distance that was kept and is still run as 1,609.344 m, which is why the 1500 m is only ever a "metric mile" in quotation marks — it is 109 m shorter.

An American football field is exactly 100 yards between the goal lines, 91.44 m, with two end zones of 10 yards each bringing the total to 109.73 m. Every unit of the game is a yard: ten to a first down, fifteen for a penalty, a quarterback's season measured in passing yards. No other sport counts in the unit that intensively, and no metric country has an equivalent that uses it at all.

Cricket is the other survivor and it uses the yard in exactly one place. The pitch is 22 yards, 20.1168 m, which is a chain — the surveying unit of 66 feet that also set the length of a furlong and the size of an English acre. The number was inherited from land measurement rather than chosen for the game, which is why it converts to nothing round.

Course cards in the United States, the United Kingdom and Ireland are in yards; cards in continental Europe, and often in Australia, are in metres. A 400 m hole is 437 yards and a 350 m hole is 383 — a full club longer than the metre figure suggests to a player who reads it as a yardage. Playing a metric card as though it were imperial means being short on every approach.

Rangefinders and GPS units are the place this actually bites, because most of them will display either unit and the setting is easy to leave wrong. A device reading 150 to the pin in metres is 164 yards, and the difference between a 150-yard club and a 164-yard club is not subtle. The conversion is trivial and the failure is entirely about which unit the number was in when it was read.

Metres to yards is add ten per cent, then take a little off. 200 m gives 220 minus about 1.3, so 218.7 yards against a true 218.72. The correction is 0.58 per cent — a tenth is slightly too generous — and for anything under a few hundred metres the uncorrected figure is inside a yard.

Going the other way, take a tenth off and add a small amount back: 300 yards gives 270 plus 4.3, so 274.3 m against 274.32. Both estimates are more than good enough for a distance that will be paced out or hit with a club, and neither is good enough for a race distance, a certified course or anything with a record attached to it.

The conversion is exact and the input usually is not. A course card saying 400 m has been rounded to the nearest metre at best and often to the nearest five, so 437.45 yards is claiming a hundredth of a yard from a figure with a couple of metres of slack in it. Round the answer back to the precision the source had: 437 yards, and no decimal.

Where the metric figure is a translation of an imperial one, the rounding has already happened once. A pitch described as 20 m is a 22-yard cricket pitch rounded down by 12 cm; a field described as 91 m is a 100-yard field rounded down by 44. Converting those back gives 21.87 and 99.52 yards, and the missing fractions are somebody else's rounding, not an error in this arithmetic.

Association football does something unusual with this conversion: the Laws of the Game specify a pitch as 90 to 120 m long and 45 to 90 m wide, and give the imperial equivalents as 100 to 130 yards and 50 to 100. Those pairs are not conversions of each other — 90 m is 98.4 yards, not 100, and 120 m is 131.2, not 130. Each list is a set of round numbers in its own system, and the imperial one sits a little inside the metric one at both ends.

The gap is deliberate and worth noticing whenever a governing body publishes both. Converting the metric limit exactly would produce 98.43 yards, which is not a number anybody can mark out with a tape and a corner flag, so the imperial version is rounded inward to stay inside the metric one. Where two official figures disagree by a per cent or so, the usual explanation is this — not an error, but two independently round descriptions of the same permitted range.