How-To Guide

How to Calculate BMI Manually

BMI is a fast screening ratio based on weight and height. The arithmetic is easy, but the result should be interpreted with other health markers rather than alone.

4 min read Updated April 8, 2026

Quick steps

  1. In metric units, divide weight in kilograms by height in meters squared.
  2. In imperial units, multiply weight in pounds by 703 and divide by height in inches squared.
  3. Round to about one decimal place.
  4. Use BMI as a reference point, not a full diagnosis.

Metric formula

BMI = weight (kg) / height (m)^2. If someone weighs 68 kg and is 1.72 m tall, the BMI is 68 / 1.72^2.

Imperial formula

BMI = weight (lb) x 703 / height (in)^2. If height is split into feet and inches, convert it to total inches first.

Read the result carefully

BMI works as a fast screen, but it does not describe total body composition or overall health by itself.

  • More muscle can push BMI higher
  • Waist size, body fat, age, and sex still matter
  • Health decisions should use professional guidance when needed

Frequently Asked Questions

Does a normal BMI always mean someone is healthy?expand_more

No. BMI is one screening signal and should be read with other measures such as blood pressure, body fat, and lifestyle.

Can I use centimeters directly?expand_more

For manual metric math, convert centimeters to meters first. For example, 172 cm becomes 1.72 m.

Is BMI accurate for athletic people?expand_more

Not always. More muscle can push BMI up even when body fat is moderate.

Try the BMI calculator

Check BMI in metric or imperial units and review the category instantly.

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