BMI Calculator (Imperial)

When to use it

Scales at home read pounds and tape measures read feet and inches, while the charts, forms and apps you compare against may want a BMI number. This page converts the two measurements into the familiar screening figure, so you never convert to kilograms first, which is where most mistakes happen.

Treat it as a snapshot of one relationship — weight against squared height — not as a verdict on health. BMI says nothing about muscle, bone, body shape, age, pregnancy or fitness, and the bands beneath the number come from public health guidance rather than a diagnosis. It is a starting point for a conversation, never the end of one.

How the maths works

BMI = weight in pounds × 703 ÷ height in inches squared. The 703 is the constant that puts imperial units on the same scale as the metric formula, weight in kilograms divided by height in metres squared. The tool prints one decimal place and then names the general adult band: under 18.5 underweight, 18.5 to 24.9 normal weight, 25 to 29.9 overweight, 30 and above the obesity range.

A worked example

Someone weighs 175 lb and measures 70 inches (5 ft 10 in).

1. Square the height: 70 × 70 = 4,900.
2. Multiply the weight by 703: 175 × 703 = 123,025.
3. Divide: 123,025 ÷ 4,900 = 25.107.
4. Round to one decimal: 25.1, which the tool labels overweight.

The metric page agrees: 175 lb is about 79.4 kg and 70 inches about 177.8 cm, and 79.4 ÷ 1.778² = 25.1 as well.

Reference values for common heights

Compare the second and third rows: 150 lb sits at 22.8 on the taller frame and 24.2 on the shorter one, so height does most of the work. A number near a boundary, such as 24.9, is not a hard line.

Common mistakes

• Entering height in feet. Typing 5.9 for 5 ft 10 in gives a BMI of about 3,527 — the field needs inches, and 5 ft 10 in is 70 in.
• Weighing at different times. Food, drink and clothing can move a reading by a kilo or two, enough to cross a band boundary, so keep the routine steady.
• Reading it as a diagnosis. A muscular person can sit in the overweight band while carrying very little fat, and a thin person can still carry risky visceral fat.
• Using adult bands for children. Under 18 the figure is read against age and sex percentile charts.

Keep exploring

• BMI Calculator — the same calculation in kilograms and centimetres.
• Body Fat Estimate (US Navy Method) — a tape-measure estimate that adds waist and neck to the picture.
• Ideal Weight Calculator — a band of weights from classic formulas for your height.
• Guide: BMI, Calories and Water Intake.