How do you estimate weight in mid arm circumference?

January 8, 2026 •

3 min read

According to a study published in the Emergency Medicine Journal, a simplified formula using mid-arm circumference can accurately estimate weight in adults and adolescents within 10% of their actual weight in over 60% of cases. Mid-upper arm circumference (MUAC) is a simple, quick, and effective anthropometric procedure used as a proxy for body weight and overall nutritional status, especially in resource-limited settings or emergencies where weighing scales are not available.

Quick Summary

This article details how to use mid-upper arm circumference (MUAC) to estimate weight, outlining the measurement technique and various formulas for different age groups. It explains the applications of MUAC in clinical and emergency settings and discusses the accuracy and limitations of this anthropometric tool.

Key Points

Accurate Measurement: Always measure the circumference at the midpoint of the upper arm, between the shoulder and elbow, using a non-stretchable tape for reliability.
Adult Formula: A common formula for adults and adolescents (≥16 years) is Weight (kg) = (4 x MUAC in cm) - 50.
Children's Use: For children under 11, MUAC is primarily a nutritional screening tool using color-coded bands rather than for direct weight estimation.
Not a Replacement for Scales: MUAC provides an estimate, which is valuable in emergencies but should not replace direct weighing when possible.
Watch for Edema: Conditions like edema can impact accuracy by artificially increasing the MUAC reading, potentially masking true nutritional status.
Track Changes Over Time: Repeated MUAC measurements can effectively track weight gain or loss in individuals over time, indicating the success of dietary interventions.
Use in Screening Tools: MUAC is a valid component of nutritional screening tools, such as the MUST, where a measurement below 23.5 cm can signal nutritional risk.

Understanding Mid-Upper Arm Circumference (MUAC)

Mid-Upper Arm Circumference (MUAC) measures the circumference of the upper arm at its midpoint, between the shoulder and the elbow. This measurement indicates muscle mass and subcutaneous fat, making it useful for assessing nutritional status, particularly for identifying wasting or acute malnutrition. The process is quick and non-invasive, requiring only a flexible measuring tape.

MUAC has traditionally been used for malnutrition screening in children, with color-coded tapes aiding rapid identification of those at risk. Its use has expanded to adults and adolescents, especially when weighing isn't possible, such as during emergencies or in settings without weighing scales.

Step-by-Step Guide to Measuring MUAC

Accurate MUAC measurement is essential for reliable weight estimation. Follow these steps:

Prepare the patient: Ensure the arm is bare and relaxed. The non-dominant arm is typically used.
Locate the landmarks: With the arm bent at 90 degrees, find the acromion process (shoulder top) and the olecranon process (elbow tip).
Find the midpoint: Measure and mark the midpoint between the two landmarks.
Take the measurement: With the arm relaxed, place the tape around the marked midpoint. Ensure the tape is snug but not tight. Read the measurement to the nearest millimeter.
Record and repeat: Record the measurement and consider taking a second reading for accuracy.

Formulas to Estimate Weight from MUAC

Several formulas exist for estimating weight from MUAC, varying by age group. These are particularly useful in emergency situations when direct weighing is not possible.

Adults and Adolescents (≥16 years): A simplified formula is often cited for emergency use:
- Weight (kg) = (4 x MUAC in cm) - 50
- This formula has shown promise in providing estimates within 10-30% of actual weight for this age group.
Children (Aged 6-59 months): MUAC is primarily a malnutrition screening tool with specific cut-off points. A MUAC below 11.5 cm, for instance, indicates severe acute malnutrition. While some studies provide regression formulas for specific child populations, they are less generalized for broad application.

How Accurate and Reliable is MUAC for Weight Estimation?

MUAC's accuracy for weight estimation varies depending on the population and formula used. While a good screening tool for malnutrition compared to Weight-for-Height Z-score, its direct weight estimation reliability is inconsistent.

Correlation: MUAC is positively correlated with body weight and BMI.
Population differences: Accuracy varies across populations due to differences in body composition and age.
Age limitations: The (4 x MAC) - 50 formula, for example, is less accurate for children aged 1-10.9 years.
Conditions affecting MUAC: Edema can falsely increase MUAC, impacting accuracy.

Comparison Table: MUAC Estimation vs. Traditional Weighing


Feature	MUAC-Based Estimation	Traditional Weighing Scale
Equipment	Simple, low-cost tape measure	Specialized, often expensive, weighing scales
Portability	Highly portable and easy to carry	Often bulky and requires stable, level ground
Ease of Use	Quick and simple, minimal training required	Can be challenging with immobile or uncooperative patients
Environment	Suitable for field, remote, or emergency settings	Requires a stable surface; not always feasible in all settings
Precision	Provides an estimate; accuracy varies by formula and population	Provides a precise, direct measurement
Scope	Primarily used for nutritional screening and emergency weight estimation	Standard method for precise weight measurement in clinical practice
Limitations	Less accurate for direct weight, poor for infants (<6 months)	Cannot be used with immobile patients or in certain emergencies

Conclusion

Mid-upper arm circumference is a practical tool for estimating weight when scales are unavailable, particularly in emergency situations. While not as precise as weighing, it offers a rapid alternative for nutritional screening and weight estimation, especially in adults and adolescents using formulas like Weight (kg) = (4 x MUAC) - 50. It is effective for assessing nutritional status using age and population-specific cut-offs. Proper measurement techniques and understanding limitations are crucial for healthcare workers and caregivers using MUAC as a screening or monitoring tool.

Further reading: For more information on validating MUAC-based weight estimation for adults and adolescents, refer to the study "Mid-arm circumference can be used to estimate weight of adult and adolescent patients" on ResearchGate.

Optional: A Quick Note on the Malnutrition Universal Screening Tool (MUST)

MUAC can be incorporated into nutritional screening tools like MUST. For adults, a MUAC under 23.5 cm can indicate a likely BMI below 20 kg/m², suggesting potential malnutrition risk.

Frequently Asked Questions

No, MUAC does not provide an exact weight. It is an estimation tool, primarily used for screening nutritional status and estimating weight when scales are unavailable, such as in emergency or field settings.

A widely referenced simplified formula for adults and adolescents aged 16 and older is: Weight (kg) = (4 x MUAC in cm) - 50. Studies have shown this to be reasonably accurate in a significant percentage of cases.

Measure the MUAC on the child's left or least affected arm. First, locate the midpoint between the shoulder bone and elbow tip. With the arm relaxed, wrap a tape measure around this midpoint, ensuring it's snug but not too tight. Record the measurement.

MUAC's reliability for direct weight estimation decreases significantly in younger children. It is more accurately used as a screening tool to assess acute malnutrition in children between 6 and 59 months using specific cut-off points, like 11.5 cm for severe malnutrition.

In adults, particularly within the context of screening tools like MUST, a MUAC of less than 23.5 cm can be used as an indicator that the person's BMI is likely below 20, suggesting potential underweight or nutritional risk.

Yes, taking repeated MUAC measurements over time can effectively monitor changes in body weight and nutritional status. A consistent increase suggests weight gain, while a decrease indicates weight loss.

Only a flexible, non-stretchable measuring tape (ideally a specialized MUAC tape) and a pen to mark the midpoint are needed. This makes it a highly portable and accessible tool.