What this calculator does
Height is needed for BMI, for drug dosing and for nutritional assessment, but a patient who cannot stand or lie straight cannot be measured directly. The Chumlea equations estimate it from knee height, which can be measured in a bed or a chair.
Knee height works because the lower leg keeps its proportion to overall height through adult life, even as spinal compression reduces standing height. Each additional centimetre of knee height adds roughly 1.9 cm of estimated stature.
The formula
Knee height is multiplied by a fitted coefficient and added to a constant, with separate equations by sex and race. The equations for women also subtract a small amount per year of age.
| Term | Meaning |
|---|---|
| Knee height | Measured from the sole of the foot to the front of the thigh with the knee bent at a right angle. |
| Chumlea equations | Regression equations published for estimating stature where direct measurement is not possible. |
| Stature | Standing height, which is what the estimate reproduces. |
The inputs explained
| Field | What to enter |
|---|---|
| Knee height (cm) | Knee height in centimetres, measured with the knee and ankle both at right angles. |
| Age (years) | Age in years. It appears in the equations for women only. |
| Sex | Sex, which selects between equation sets. |
| Race | Race, which the original equations were fitted separately for. |
When to use it
Assessing a bedridden patient
Nutritional screening and BMI both need a height figure that cannot be measured directly.
Dosing by body surface area
Height feeds into surface area calculations used in some drug dosing.
Estimating height in advanced age
Spinal changes and contractures can make standing measurement unreliable or impossible.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How does knee height translate to stature?
Three knee heights for the same patient profile.
| Knee height | Estimated height | In feet & inches |
|---|---|---|
| 45 cm | 156.5 cm | 5 ft 2 in |
| 50 cm | 165.9 cm | 5 ft 5 in |
| 55 cm | 175.3 cm | 5 ft 9 in |
Questions
How accurate is the estimate?
The original studies reported standard errors of roughly 3 cm, so an individual estimate can be several centimetres from true standing height. That is usually acceptable for nutritional screening and less so for anything needing precision.
Why is race one of the inputs?
Because the original equations were fitted separately on different population groups and produced different coefficients. That reflects how the research was conducted rather than a biological necessity, and the approach has been questioned since.
How should knee height be measured?
With the knee and ankle each bent to a right angle, using a sliding caliper from the sole of the foot to the anterior surface of the thigh just above the knee. Technique matters, and an inconsistent measurement carries straight through to the estimate.
Are there alternatives?
Yes, including demi-span, arm span and ulna length, each with its own published equations. Which is used depends on what can be measured reliably in the patient concerned.
For a dosing weight in larger patients, see the adjusted body weight calculator. For weight-for-height, see the BMI calculator.