BMI (Body Mass Index) is a quick screening tool to assess if your weight is healthy for your height. This guide explains how to calculate it and what the numbers mean.
BMI Formula
Metric: BMI = weight(kg) / height(m)². Example: 70kg, 1.75m gives BMI = 70 / (1.75 × 1.75) = 22.9.
Imperial: BMI = (weight(lbs) / height(inches)²) × 703. Example: 154lbs, 5'9" (69 inches) gives BMI = (154 / 69²) × 703 = 22.7.
BMI Categories (WHO Standard)
- Below 18.5: Underweight
- 18.5 - 24.9: Normal weight
- 25.0 - 29.9: Overweight
- 30.0 - 34.9: Obese Class I
- 35.0 - 39.9: Obese Class II
- 40.0 and above: Obese Class III
How to Calculate BMI on ToolHub
Step 1: Open BMI Calculator. Visit toolhubpro.co/tools/bmi-calculator.
Step 2: Select your unit system. Choose Metric (kg/cm) or Imperial (lbs/feet/inches).
Step 3: Enter your measurements. Input your height and weight accurately.
Step 4: View results. See your BMI number, category, healthy weight range for your height, and personalized health tips.
BMI Limitations
BMI does not account for muscle mass (athletes may show overweight), age-related changes in body composition, gender differences in fat distribution, or ethnicity (Asian populations have higher risk at lower BMI values).
Better measurements to combine with BMI include waist circumference, waist-to-height ratio, and body fat percentage.
Healthy BMI by Age
- Age 20-39: 18.5 - 24.9
- Age 40-59: 18.5 - 24.9
- Age 60+: 23 - 27.9 (a slightly higher range is acceptable)
For children under 18, BMI percentile is used instead of fixed ranges. Consult a pediatrician for interpretation.
Frequently Asked Questions
How accurate is BMI? BMI is a screening tool, not a diagnosis. It is accurate for most adults but less accurate for athletes and elderly individuals.
What BMI is ideal? For most adults, a BMI of 20-22 is considered optimal for longevity according to research.
Should I see a doctor about my BMI? Consult a healthcare provider if your BMI is below 18.5 or above 30.
Note: This calculator provides general information and is not medical advice.