What this converter does
This converter changes a linear measurement between millimetres, centimetres and inches by converting to millimetres and back out again.
It exists because published osteometric equations use different units, and applying a centimetre equation to a millimetre measurement is a factor-of-ten error that produces an obviously absurd result — or, worse, a plausible one. This is a teaching aid, not a casework tool.
Convert measurement
Before you convert
- Check which unit the equation you are using expects. Trotter and Gleser's stature equations use centimetres; many osteometric recording standards use millimetres.
- Record measurements in the unit you took them in, and convert only when applying an equation.
- The output is shown to four decimal places, which is well beyond measurement precision. Round appropriately when reporting.
- One inch is exactly 25.4 millimetres by definition, so inch conversions are exact rather than approximate.
A femur measured at 460 and entered into a centimetre equation gives an absurd stature that anyone would catch. A femur measured at 46 and entered into a millimetre equation gives a small number that is also obviously wrong. The dangerous case is a partial error — mixing units between two steps of a chain — where the result stays in a plausible range.
How this calculator works
Conversion through a common base:
Millimetres = value × from-unit factor
Result = millimetres ÷ to-unit factor
Factors: millimetres 1 · centimetres 10 · inches 25.4Converting through a single base unit rather than using a direct conversion for each pair means only three factors are needed rather than six, and adding another unit requires one factor rather than several.
Worked example: 450 millimetres
Using the default figures — 450 with millimetres selected as the source and centimetres as the target:
- In millimetres: 450 × 1 = 450
- In centimetres: 450 ÷ 10 = 45.0000
A 450 mm femur is 45.0 cm, which fed into the Trotter and Gleser equation used on the stature page gives (2.32 × 45) + 65.53 = 169.93 cm. Entering 450 into that same equation would give 1,109.53 cm — eleven metres, and obvious. The genuinely risky errors are the ones that stay believable.
Common mistakes
- Assuming an equation's units. Check the source rather than inferring from the coefficient.
- Converting more than once in a chain. Convert at the point of use, not repeatedly.
- Reporting four decimal places. Round to the precision of the original measurement.
- Mixing units between steps. The error that produces a plausible wrong answer.
- Using an approximate inch conversion. 25.4 mm is exact.
Frequently asked questions
Which unit should I record measurements in?
Millimetres are standard in most osteometric recording protocols, because they avoid decimals for typical bone dimensions and match the resolution of an osteometric board. Convert to whatever an equation requires at the point of applying it, and record the original measurement unchanged.
Why do published equations use different units?
Historical convention as much as anything. Trotter and Gleser's mid-twentieth-century work used centimetres; later recording standards standardised on millimetres. Equations are not revised into new units because doing so would change the published coefficients and invite transcription errors.
How precise are osteometric measurements?
An osteometric board reads to a millimetre, and repeatability between analysts is typically within one or two millimetres for well-defined measurements on intact bones. Damaged or eroded landmarks reduce that considerably, and the measurement definition matters as much as the instrument.
Should I convert before or after applying an equation?
Before, into the unit the equation expects, and then leave the result in whatever unit the equation produces. Converting the output afterwards adds an unnecessary step and another opportunity for error.
Is what I enter stored?
No. Values are processed entirely in your browser and never transmitted or retained.
Related tools
References
- GOV.UK — Forensic Science Regulator codes of practice on measurement and reporting
- National Institute for Health and Care Excellence — clinical guidance on measurement standards
Sources are checked at publication and can change — how I choose and check references.