MUAC Calculator NHS
This independent UK tool helps interpret an adult mid-upper arm circumference (MUAC) measurement using BAPEN guidance. MUAC can support nutritional screening when height or weight cannot be measured reliably, but it does not produce a standalone MUST score.
Adult MUAC interpretation tool
How to measure MUAC
BAPEN recommends using the left arm if possible. Identify the shoulder tip (acromion) and elbow point (olecranon), measure between them and mark the midpoint. Let the arm hang loose, then measure around the midpoint with the tape snug but not tight.
How the result is interpreted
BAPEN states that an adult MUAC below 23.5 cm suggests BMI is likely to be below 20 kg/m². A MUAC above 32.0 cm suggests BMI is likely to be above 30 kg/m². These are broad estimates rather than an exact BMI calculation. MUAC is specifically described as not being designed to generate a score for MUST.
Monitoring change over time
When MUAC is used to monitor change, BAPEN advises repeated measurements under similar conditions, preferably taking two measurements on each occasion and using their average. A change of at least 10% is likely to indicate that weight and BMI have changed by about 10% or more, but absolute values cannot be assigned from MUAC change alone.
Worked example
An adult MUAC measurement of 22.8 cm is below 23.5 cm. Under BAPEN guidance this suggests the person’s BMI is likely to be below 20 kg/m². It does not by itself diagnose malnutrition or create a MUST score; the full nutritional picture and clinical judgement remain important.
Limitations
This adult interpretation should not be applied to children using adult cut-offs. MUAC can be affected by measurement technique and individual body composition. When accurate height and weight are available, use them for BMI and complete the full nutritional screening process where appropriate.
Authoritative Sources
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FAQs
What does MUAC stand for?
MUAC means mid-upper arm circumference, an anthropometric measurement used as part of nutritional assessment and screening.
Does MUAC calculate a MUST score?
No. BAPEN states that MUAC can help estimate a BMI category when measurements are difficult, but it is not designed to generate a MUST score.
What does MUAC below 23.5 cm mean in adults?
It suggests BMI is likely to be below 20 kg/m². It is not a diagnosis on its own.
What does MUAC above 32 cm mean?
BAPEN states that BMI is likely to be above 30 kg/m², but MUAC remains an estimate rather than an exact BMI measurement.
Disclaimer: This tool is for adult nutritional-screening information only. It does not diagnose malnutrition and does not replace the full MUST process, a dietetic assessment or clinical judgement.