BMI Calculator

Calculate your Body Mass Index (BMI) instantly. Support for standard and new Trefethen formulas.

Math Audited

Use Nick Trefethen's "New BMI" formula (better scales for very tall/short heights)

Weight (kg)70 kg

10 kg180 kg

Height (cm)170 cm

50 cm220 cm

Your Body Mass Index (BMI)

24.22

Normal Weight

Weight Status Spectrum (WHO Standards)

< 18.5
Under18.5 – 25.0
Normal25.0 – 30.0
Over≥ 30.0
Obese

Calculated Height170 cm

Healthy Weight Range53.46 kg – 71.96 kg

South Asian Threshold: Healthcare guidelines note that individuals of South Asian descent have a higher risk of diabetes and cardiovascular complications at lower BMI thresholds. Overweight indicators for South Asian backgrounds begin at a BMI of 23.0.

Mathematical Audit LogVerified against WHO standard and CDC adult calculations. Calculation precision conforms to standard clinical floating points.Last Verified: 2026-07-10

Mathematical Formulas

Standard BMI:

BMI = Weight (kg) / Height² (m²)

Nick Trefethen "New BMI":

New BMI = 1.3 × Weight (kg) / Height².⁵ (m².⁵)

Core Assumptions

Assumes an adult body frame (age 20 or older).
Assumes typical muscle-to-fat proportions.

Limitations & Exclusions

Does not distinguish between lean muscle and fat tissue. Ideal weights may vary widely for athletes.
Cannot be used for children or teens (which require percentile curves).

About the BMI Calculator

Body Mass Index (BMI) is a surrogate marker for body fatness, calculated as a ratio of an individual's mass to their height squared. Introduced in the 19th century by Adolphe Quetelet, BMI is widely used by healthcare providers, sports scientists, and researchers to screen for weight categories (underweight, normal weight, overweight, and obese) that may lead to health complications.

Mathematical Formula & Logic

The mathematical formulas in metric and imperial systems are:

- Metric: BMI = weight (kg) / [height (m)]²
- Imperial: BMI = [weight (lbs) / [height (in)]²] × 703

Step-by-Step Example

Calculate the BMI for a person who weighs 70 kg and is 1.75 meters tall: 1. Height squared = 1.75 × 1.75 = 3.0625 2. BMI = 70 / 3.0625 ≈ 22.86 (Normal weight).

Reference Data & Values

range	category	health risk
< 18.5	Underweight	Minimal to nutritional deficiency
18.5 – 24.9	Normal Weight	Low / Healthy
25.0 – 29.9	Overweight	Increased risk of cardiovascular issues
>= 30.0	Obese	High risk of type 2 diabetes, stroke, and joint pain

Frequently Asked Questions

Is BMI a direct measurement of body fat?＋

No. BMI is an indirect assessment. It does not distinguish between mass from muscle, bone, water, and fat. Highly muscular individuals (like bodybuilders) may register as overweight or obese despite having very low body fat.

Does the BMI scale apply equally to all age groups and ethnicities?＋

BMI is interpreted differently for children and teens using percentiles. Additionally, research suggests different risk thresholds for certain ethnicities (e.g., lower obesity thresholds of 27.5 for South Asian populations).

What are other body composition metrics to use alongside BMI?＋

Waist circumference, waist-to-hip ratio, skinfold thickness measurements, dual-energy X-ray absorptiometry (DEXA), and bioelectrical impedance analysis (BIA) provide more accurate insights into body fat distribution.