sprytools

BMI Calculator

Calculate your Body Mass Index (BMI) with metric or imperial inputs. Get WHO category, ideal weight range for your height, and Harris-Benedict BMR estimate. Free, 100% client-side.

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BMI Calculator

Enter your height and weight to instantly compute your Body Mass Index (BMI), see your WHO category, check your ideal weight range, and get a BMR (Basal Metabolic Rate) estimate. All calculations run entirely in your browser — no data is sent to any server.

What the Results Mean

BMICategoryWHO Classification
< 18.5UnderweightGrade 1–3 (< 16 severe)
18.5 – 24.9Normal weight—
25.0 – 29.9OverweightPre-obese
30.0 – 34.9Obese (Class I)Moderate
35.0 – 39.9Obese (Class II)Severe
≥ 40Obese (Class III)Very severe

Ideal Weight Range

The ideal weight range shows the weight span that corresponds to a Normal weight BMI (18.5–24.9) for your height. It is calculated as:

Harris-Benedict BMR

Basal Metabolic Rate (BMR) is the energy your body needs at complete rest. Provide your age and sex to calculate it using the revised Harris-Benedict equations:

Multiply BMR by your activity factor to estimate total daily energy expenditure (TDEE).

Imperial Units

Select Imperial to enter weight in pounds (lbs) and height in feet and inches. The tool converts to metric internally before calculating:

Disclaimer

BMI is a population-level screening tool. It does not account for muscle mass, bone density, age-related body composition changes, or ethnic differences in fat distribution. It is not a substitute for medical advice.

FAQ

How is BMI calculated?

BMI = weight (kg) ÷ height² (m). For example, 70 kg at 175 cm gives 70 ÷ 1.75² = 22.9. For imperial units, the tool converts pounds to kilograms and feet/inches to centimetres before calculating.

What are the WHO BMI categories?

The World Health Organization defines four main categories: Underweight (BMI < 18.5), Normal weight (18.5–24.9), Overweight (25–29.9), and Obese (≥ 30). Obesity is further split into Class I (30–34.9), Class II (35–39.9), and Class III (≥ 40).

What is the ideal weight range?

The ideal weight range shows the minimum and maximum body weight that corresponds to a "Normal weight" BMI (18.5–24.9) for your height. It is a guideline, not a personal target — muscle mass, bone density, and age all affect healthy weight.

What is BMR and how is it calculated?

BMR (Basal Metabolic Rate) is the number of calories your body burns at complete rest. This tool uses the Harris-Benedict (revised) equation: for men, BMR = 88.362 + (13.397 × kg) + (4.799 × cm) − (5.677 × age); for women, BMR = 447.593 + (9.247 × kg) + (3.098 × cm) − (4.330 × age). Provide age and sex to see your BMR estimate.

Is BMI a reliable health indicator?

BMI is a simple screening tool, not a diagnostic measure. It does not account for muscle mass, fat distribution, ethnicity, age, or sex differences. Always consult a healthcare professional for medical advice.