Sport unit converter, and the names that mean two different things
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Every factor on this page is a definition rather than a measurement. Since nineteen fifty nine the yard has been exactly nought point nine one four four metres and the pound exactly nought point four five three five nine two three seven kilograms, agreed by treaty, so the only rounding here is the one your screen does.
Results
Things that are called the same and are not
| What both go by | The imperial one, converted | The metric one | Gap |
|---|---|---|---|
| The bar | |||
| Two plates a side | |||
| Four plates a side | |||
| The short sprint | |||
| The mile |
The first three rows are in kilograms and the last two in metres. Each row is one name for two different things.
A converter is usually a boring page, and this one would be too if the two systems only disagreed about numbers. They also disagree about names. A gym with pound plates and a gym with kilo plates both call the same lift four plates a side, and the two lifts are three point seven kilograms apart, a little over two in a hundred. Nobody is rounding badly. The bar and the plates were simply never the same objects.
The same thing happens at the milestone everybody quotes. Two plates a side means two hundred and twenty five pounds in one gym and one hundred kilograms in the other, and the first is two kilograms heavier. Anyone who converts their own numbers with a round factor and then compares them to a table from the other side of the ocean is comparing two slightly different feats.
Running has the sharper version of it. The famous short sprint is forty yards, which is thirty six and a half metres, so a forty metre dash is more than nine in a hundred longer. Put the two stopwatch numbers side by side and you are not ranking two athletes, you are ranking two races. The gap is far too large to be absorbed by any conversion of the time itself.
The mile is the last of them, and it hides the subtlest trap. Fifteen hundred metres is nearly seven in a hundred short of a mile, and the tempting fix is to scale a fifteen hundred time by that same ratio. It does not work, because pace decays as distance grows: the honest scaling is a little steeper, and on a four minute fifteen hundred the difference is about a second. A second is the whole margin of most finishes.
None of this makes either system better. It is a warning about a habit: converting the number and keeping the name. The number converts exactly, by treaty. The name does not convert at all.
Why is four plates a side not the same lift everywhere?
Because the plates were never the same objects. A pound gym stacks a forty five pound bar and forty five pound plates; a kilo gym stacks a twenty kilogram bar and twenty kilogram plates. Both are described with the same sentence.
Converted to one scale, the first is a little over one hundred and eighty three and a half kilograms and the second is one hundred and eighty exactly. The gap is three point seven kilograms, a little over two in a hundred, and no amount of careful rounding removes it.
Is two hundred and twenty five pounds the same as one hundred kilograms?
No. It is a shade over one hundred and two, so the pound milestone is about two kilograms heavier than the metric one people compare it with.
Both are famous because they are round in their own system, not because they are the same weight. Someone converting their own number and then reading a table from the other side is comparing two slightly different feats.
Can I compare a forty yard time with a forty metre time?
Not directly. Forty yards is thirty six and a half metres, so the metre version is more than nine in a hundred longer, and that is far too much to absorb by adjusting the time a little.
Putting the two stopwatch numbers next to each other ranks two races, not two athletes. If you need them on one scale, convert the distance first and then scale the time, and treat the result as an estimate rather than a result.
How do I turn a fifteen hundred metre time into a mile time?
Not by multiplying by the distance ratio, which is the obvious move and the wrong one. Fifteen hundred metres is nearly seven in a hundred short of a mile, so the ratio is a little over one point zero seven.
The catch is that pace decays as distance grows, so the honest scaling is slightly steeper than the pure ratio. On a four minute fifteen hundred the plain ratio gives about two hundred and fifty seven and a half seconds and the decay-aware one about two hundred and fifty eight and a half. One second decides most finishes.
Are these factors exact, or rounded?
Exact, and by agreement rather than by measurement. Since nineteen fifty nine the yard is defined as nought point nine one four four metres and the pound as nought point four five three five nine two three seven kilograms, which is why the mile lands on one thousand six hundred and nine point three four four metres with nothing after it.
So every figure on this page is as precise as the space it is printed in. The uncertainty in a conversion is never in the factor; it is in whether the two things being converted were the same thing to begin with.
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