Feed Unit Converter
The conversion is not where the error comes from. An inch has been exactly 0.0254 m and a pound exactly 0.453 592 37 kg since 1959 — those are definitions, not measurements. Everything that goes wrong happens when you round to the number of decimals a feed field accepts, and most converters do not tell you what that cost.
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What two decimal places costs
One pound is 0.45359237 kg. A field that accepts two decimals stores
0.45 — 0.79 %
light. On a single item that is invisible. On a consignment it is the difference
between one shipping band and the next, and it always rounds the same direction, so the error
accumulates rather than cancelling out.
Compare 10 inches, which is exactly 25.4 cm and survives two decimals with nothing lost. Whether rounding costs you anything depends on the number, and that is precisely what this tool reports instead of hiding.
Where the factors come from
Only two constants are written down here. Every other imperial unit is derived from them by definition — twelve inches to a foot, sixteen ounces to a pound — so there are two numbers to verify rather than eight, and our tests check the derivations against each other.
| Unit | In base units | Where the factor comes from |
|---|---|---|
mm millimetre | 0.001 m | SI prefix — exact by definition. |
cm centimetre | 0.01 m | SI prefix — exact by definition. |
m metre | 1 m | SI base unit — the reference every other length here converts through. |
in inch | 0.0254 m | Exactly 0.0254 m — published by NIST in bold, meaning exact. |
ft foot | 0.30479999999999996 m | Twelve inches, so exact for the same reason. |
yd yard | 0.9144 m | Thirty-six inches — 0.9144 m exactly, as the 1959 agreement defines. |
g gram | 0.001 kg | SI prefix — exact by definition. |
kg kilogram | 1 kg | SI base unit — the reference every other mass here converts through. |
lb pound (avoirdupois) | 0.45359237 kg | Exactly 0.453 592 37 kg by the 1959 international agreement. NIST publishes it rounded to seven significant digits (4.535 924 E-01); our constant agrees with that rounding. |
oz ounce (avoirdupois) | 0.028349523125 kg | One sixteenth of a pound, so exact for the same reason. |
A mixed column is worse than a wrong one
A feed field carries one unit for the entire column. If some rows are inches and some are centimetres, every row that does not match the declared unit is silently mislabelled — and nothing rejects it, because each individual number is perfectly valid. Paste the column and this tool will say which units it found.
Every check this tool runs (6 rules)
UNIT-R01 Rounding costs more than it looks
The conversion itself is exact; what loses accuracy is rounding to the number of decimals a feed field accepts. One pound is 0.453 592 37 kg, so a field that takes two decimals stores 0.45 — nearly 0.8 % light. On one item that is nothing; across a pallet it can move you into a different shipping band.
Fix: Store more decimals if the field allows it, or convert from the original unit rather than from an already-rounded value.
Source: Imperial factors are the exact definitions from the 1959 international yard and pound agreement. The inch is published by NIST in bold, which in their notation means exact; the pound is published rounded to seven significant digits, and our constant agrees with that rounding. Every other imperial unit is derived from those two by definition (12 in = 1 ft, 16 oz = 1 lb) rather than carrying its own constant, and our tests check the derivations against each other.
UNIT-P01 The factor is exact
These are not measured approximations. The inch has been exactly 0.0254 m and the pound exactly 0.453 592 37 kg since 1959, which means any error in a converted value came from rounding, not from the conversion.
Source: Imperial factors are the exact definitions from the 1959 international yard and pound agreement. The inch is published by NIST in bold, which in their notation means exact; the pound is published rounded to seven significant digits, and our constant agrees with that rounding. Every other imperial unit is derived from those two by definition (12 in = 1 ft, 16 oz = 1 lb) rather than carrying its own constant, and our tests check the derivations against each other.
UNIT-U01 Unit not recognised
The unit could not be matched to one this tool carries. Length and mass are covered; volume, area and anything temperature-related are not.
Fix: Use one of the listed codes, or spell the unit out.
Source: Imperial factors are the exact definitions from the 1959 international yard and pound agreement. The inch is published by NIST in bold, which in their notation means exact; the pound is published rounded to seven significant digits, and our constant agrees with that rounding. Every other imperial unit is derived from those two by definition (12 in = 1 ft, 16 oz = 1 lb) rather than carrying its own constant, and our tests check the derivations against each other.
UNIT-K01 Cannot convert between kinds
Length cannot become mass. When this appears in a batch it usually means a column mixes dimensions and weights, or that a units column was misaligned by one row.
Source: Imperial factors are the exact definitions from the 1959 international yard and pound agreement. The inch is published by NIST in bold, which in their notation means exact; the pound is published rounded to seven significant digits, and our constant agrees with that rounding. Every other imperial unit is derived from those two by definition (12 in = 1 ft, 16 oz = 1 lb) rather than carrying its own constant, and our tests check the derivations against each other.
UNIT-E01 Not a number
No numeric value could be read from the input.
Fix: Check for a stray currency symbol, a thousands separator, or a unit that ran into the number.
Source: Imperial factors are the exact definitions from the 1959 international yard and pound agreement. The inch is published by NIST in bold, which in their notation means exact; the pound is published rounded to seven significant digits, and our constant agrees with that rounding. Every other imperial unit is derived from those two by definition (12 in = 1 ft, 16 oz = 1 lb) rather than carrying its own constant, and our tests check the derivations against each other.
UNIT-M01 Mixed units in one column
The rows do not all use the same unit. A feed field carries one unit for the whole column, so a mixed column silently mislabels every row that does not match.
Fix: Convert the whole column to one unit before exporting.
Source: Imperial factors are the exact definitions from the 1959 international yard and pound agreement. The inch is published by NIST in bold, which in their notation means exact; the pound is published rounded to seven significant digits, and our constant agrees with that rounding. Every other imperial unit is derived from those two by definition (12 in = 1 ft, 16 oz = 1 lb) rather than carrying its own constant, and our tests check the derivations against each other.
Length and mass only. Volume, area and temperature are deliberately absent rather than approximated — temperature in particular is not a simple factor, and a converter that pretended otherwise would be wrong in a way that looks right.