BMI Calculator (Body Mass Index)

Calculate BMI, ideal weight, weight category, and healthy range in metric (kg/cm) or imperial (lbs/ft).

Height

Weight

Body Mass Index (BMI)

What is the Online BMI Calculator?

This free BMI Calculator calculates your Body Mass Index (BMI) using standard height and weight formulas. Entering your measurements generates your numerical BMI score and displays where it falls within standard reference weight categories (underweight, normal weight, overweight, and obesity classifications), alongside a statistical benchmark weight estimate. It provides a quick informational reference for general fitness tracking.

In addition to raw BMI scores, it displays your medically ideal weight (targeted at BMI 22.0), the span of your healthy weight range, and the exact weight differential required to reach your target. Built-in memory registers (MC, MR, M+, M−, MS) let you log baseline measurements for progressive wellness tracking.

Step-by-Step Guide: How to Calculate BMI

Select Unit System: Choose Metric (cm & kg) or Imperial (feet, inches & lbs).
Input Height & Weight: Enter height (e.g., 175 cm or 5 ft 9 in) and body weight (e.g., 70 kg or 154 lbs).
Click Calculate:
- BMI Value: Calculated Body Mass Index score.
- Weight Status: WHO classification (Underweight, Normal, Overweight, Obese).
- Ideal Body Weight: Optimal target weight calibrated at BMI 22.0.
- Healthy Range: Normal weight boundaries (BMI 18.5 – 24.9).
Save to Memory: Store your target weight with MS for daily fitness goal tracking.

Core BMI Formulas

Metric Formula: BMI = Weight (kg) ÷ [Height (m)]²
Imperial Formula: BMI = 703 × Weight (lbs) ÷ [Height (inches)]²
Ideal Body Weight (BMI 22.0): Ideal Weight (kg) = 22 × [Height (m)]²
Healthy Range: Min = 18.5 × Height² to Max = 24.9 × Height²

WHO Body Mass Index Categories

Underweight: BMI < 18.5
Normal / Healthy Weight: BMI 18.5 – 24.9
Overweight: BMI 25.0 – 29.9
Obesity Class I: BMI 30.0 – 34.9
Obesity Class II: BMI 35.0 – 39.9
Obesity Class III (Severe): BMI ≥ 40.0

Practical Real-World Calculation Examples

Metric Calculation (175 cm, 70 kg): BMI = 70 ÷ (1.75)² = 70 ÷ 3.0625 ≈ 22.86 (Normal Weight), Ideal Weight: 1.75² × 22 = 67.38 kg.
Imperial Calculation (5 ft 10 in, 180 lbs): Height = 70 in. BMI = 703 × 180 ÷ (70)² = 126,540 ÷ 4,900 ≈ 25.82 (Overweight).

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Frequently Asked Questions (FAQ)

What is Body Mass Index (BMI)?

Body Mass Index (BMI) is a standardized screening metric calculated from a person's height and weight (Weight in kg divided by Height in meters squared) to estimate body fat categories.

What is the formula to calculate BMI?

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

What is considered a healthy or normal BMI range?

According to the World Health Organization (WHO) and CDC, a normal, healthy BMI for adults is between 18.5 and 24.9.

How is Ideal Body Weight calculated?

Ideal body weight is medically modeled at BMI 22.0 (the statistical point associated with lowest health risk): Ideal Weight (kg) = 22 × [Height (m)]².

Does BMI distinguish between muscle mass and body fat?

No, BMI evaluates total body mass and does not directly measure body fat percentage. Muscular athletes or bodybuilders may register as overweight or obese despite low body fat.

Are BMI categories the same for men and women?

Yes, standard adult BMI categories (underweight, normal, overweight, obese) apply equally to adult men and women aged 20 and older.

Can this BMI calculator be used for children and teenagers?

This calculator is designed for adults (ages 20+). For children and teens (ages 2–19), BMI percentiles adjusted for age and sex (BMI-for-age) must be used.

Can I enter measurements in feet, inches, and pounds?

Yes, switch to the Imperial unit mode to input weight in pounds (lbs) and height in feet and inches (ft/in).

How do I calculate the weight range for normal BMI?

Multiply the square of your height in meters by 18.5 for the lower healthy boundary, and by 24.9 for the upper healthy boundary.

Is this online BMI calculator free on mobile devices?

Yes, it is 100% free with no registration or app downloads required across mobile browsers on iOS and Android.

Does this BMI calculator provide medical diagnosis or advice?

No, this tool is intended for general informational screening only. Consult a healthcare provider for comprehensive medical and body composition assessments.