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How To Calculate BMI In Metric And Imperial Units

BMI is easy to calculate, but unit mixing and rounding create confusion. This guide shows the exact setup for metric and imperial examples before you interpret the result.

Reviewed: June 28, 2026Primary topic: how to calculate bmi metric imperialEducational guidance

Metric BMI Setup

BMI = weight (kg) / height (m)2

Convert height from centimeters to meters before squaring it. For example, 175 cm becomes 1.75 m. If weight is 70 kg, the calculation is 70 / 1.752 = 22.9 after rounding.

Imperial BMI Setup

BMI = weight (lb) x 703 / height (in)2

Convert feet and inches into total inches first. For example, 5 ft 9 in becomes 69 inches. If weight is 154 lb, the calculation is 154 x 703 / 692, which is about 22.7 after rounding.

Do Not Mix Units

The most common error is entering pounds into a metric formula or centimeters into an imperial formula. Use the unit system that matches your original measurement. If you convert manually, convert both height and weight before calculating.

Read The Category Carefully

Adult BMI categories are screening ranges. They can help organize height-to-weight context, but they do not measure muscle, fat distribution, health history, blood pressure, or laboratory markers.

When To Add Another Metric

If BMI conflicts with your waist size, training status, body composition, pregnancy, age, or medical context, add waist-to-height ratio or body-fat estimation rather than recalculating BMI repeatedly.

Frequently Asked Questions

What is the easiest way to calculate metric BMI?

Use kilograms divided by height in meters squared. Convert centimeters to meters before squaring height.

Why does imperial BMI use 703?

The 703 factor converts pounds and inches into the same ratio used by the metric formula.

Should I round before or after calculating?

Round the final BMI, not the intermediate height conversion, when possible.

Sources And Further Reading

Related Guides

Metric vs Imperial BMI FormulaCompare metric and imperial BMI formulas, conversion steps, rounding differences, examples, and when BMI needs body-composition context.BMI vs Body Fat vs Waist MeasurementsCompare BMI, body-fat estimates, waist-to-height ratio, and waist-to-hip ratio so you can choose the right screening tool and interpret its limits.
These guides provide general education and help select a relevant tool. They do not diagnose a condition, prescribe treatment, or replace individualized professional guidance.