BMI Calculator

Calculate body mass index in metric or imperial units

System

Height (cm)

Weight (kg)

Your BMI

24.2Normal weight

How it works

BMI Calculator — Calculate body mass index in metric or imperial units. All processing happens in your browser — no upload, no signup, no email required. Free forever.

Last updated: 2026-05-06

Editor's note

BMI is a population-level screening number, not a verdict on a person. We keep saying this to ourselves while we build, because every BMI calculator on the internet treats the output like a medical diagnosis printed on a wristband. A muscular rugby player and a sedentary office worker can land at the same 27 and they are not in the same health bucket. We added the category note under the result for exactly this reason — so nobody hands the phone to a friend who walks away feeling labelled by a single number.

The other thing we obsess over is unit conversion. Half the wrong BMI readings out there come from someone mixing 5'7" with 154 lb in their head and typing partial metric. The form asks you to pick a system first and locks the inputs, so you cannot accidentally combine feet with kilograms. It is a small UI guardrail that prevents the most common silent error in BMI math. The formula itself is the easy part; getting clean inputs is the work.

About BMI Calculator

Body Mass Index is the most common screening number used by clinicians, insurers, and fitness apps to gauge whether a person's weight sits in a healthy range relative to their height. The formula is simple — weight in kilograms divided by height in meters squared (kg / m²) — but in practice most people get tripped up converting feet-and-inches to meters or pounds to kilograms. This calculator does the conversion for you in either direction: enter Metric (cm, kg) or Imperial (ft/in, lb) and the result is the same standard WHO BMI value.

Worked example: a 170 cm, 70 kg adult has a BMI of 70 / (1.70 × 1.70) = 70 / 2.89 = 24.22, which falls in the Normal category. The same person in imperial — 5'7" and 154 lb — produces (154 × 703) / (67 × 67) = 24.10, the small difference coming from rounding the height conversion. Categories follow the WHO adult classification: Underweight below 18.5, Normal 18.5 to 24.9, Overweight 25 to 29.9, and Obese 30 and above.

BMI is a population-level screen, not a diagnosis. It does not distinguish between muscle and fat, so a heavily-trained athlete may register as Overweight while having very low body fat, and a sedentary person with low muscle mass can sit in Normal while still carrying unhealthy visceral fat. Treat the number as one input among many — waist circumference, blood pressure, blood lipids, and lifestyle factors all matter at least as much.

How to use BMI Calculator

Pick a System: Metric (cm, kg) or Imperial (ft/in, lb).
Enter your Height — one centimeter field for metric, or feet and inches for imperial.
Enter your Weight — kilograms for metric, pounds for imperial.
Read your BMI value and the category label that appears underneath.
Switch systems at any time to cross-check the conversion if a doctor's chart used the other unit.

Common use cases

Filling in a patient intake form for a clinic that records BMI in the chart.
Tracking changes over a multi-month exercise program — record monthly BMI alongside weight to normalize for height.
Comparing your number against the WHO chart your doctor referenced after a check-up.
Calculating ideal weight range — solve the BMI formula for weight at BMI 22 to find the middle of the Normal band for your height.
Quickly converting an imperial number from a US insurance form into the metric figure your European GP wants.

Tips & common mistakes

Measure height first thing in the morning without shoes — spinal compression through the day can shave 1–2 cm off your evening height.
Weigh yourself on the same scale at the same time of day for trend tracking; absolute calibration matters less than consistency.
BMI is not designed for under-18s, pregnant or breastfeeding women, or elite athletes with high lean mass. Use age- and population-specific charts in those cases.
If your BMI sits near a category boundary, do not over-react to a single reading — daily weight fluctuates 1–2 kg from food and water alone.

Frequently asked questions

Which BMI formula is used?

Standard WHO formula: weight (kg) / height (m)². For imperial inputs we use the equivalent (lb × 703) / inches², which gives the same result.

Are the BMI categories official?

Yes — Underweight (<18.5), Normal (18.5–24.9), Overweight (25–29.9), Obese (≥30) per the WHO classification for adults.

Is BMI suitable for athletes or children?

BMI is a population-level indicator and can be misleading for very muscular individuals, pregnant women or children. Treat the number as a starting point, not a diagnosis.

What is a healthy BMI for older adults?

Several large studies suggest a slightly higher target range (around 23 to 27) is associated with the lowest mortality risk in adults over 65, partly because some weight reserve protects against illness-related muscle loss. Discuss your individual target with your doctor.

How do I compute my ideal weight from BMI?

Pick a target BMI (usually 22 as the middle of Normal) and multiply by height squared in meters. For 170 cm: 22 × 1.70² ≈ 63.6 kg. For 175 cm: 22 × 1.75² ≈ 67.4 kg.

Does waist circumference give a better signal than BMI?

For cardiometabolic risk, yes — waist or waist-to-height ratio captures abdominal fat, which is more strongly linked to disease than overall mass. Many guidelines now recommend reporting both alongside one another.

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