BMI Calculator

How to use this calculator

1. Choose Imperial (feet/lbs) or Metric (cm/kg).
2. Select your height using the ft/in dropdowns, or enter it in cm.
3. Enter your weight.
4. Click Calculate BMI.

Tip: Your result includes a visual gauge showing where you fall across the four WHO categories — Underweight, Normal, Overweight, and Obese. Scroll down for a full explanation of each range.

How it works

Body Mass Index is calculated using the formula: BMI = weight (kg) ÷ height (m)². For imperial inputs, the equivalent is: BMI = (weight (lbs) ÷ height (inches)²) × 703. The four category thresholds are defined by the World Health Organization and used by public health agencies globally as a standardized screening measure for weight-related health risk.

BMI is a screening tool, not a diagnostic one. It does not account for muscle mass, bone density, age, sex, or fat distribution. The CDC recommends using BMI alongside other assessments — such as waist circumference and clinical evaluation — for a complete health picture.

Underweight — BMI below 18.5

A BMI under 18.5 may indicate insufficient body fat or muscle mass. Potential health risks include nutritional deficiencies, weakened immune function, and bone density loss. Causes can range from high metabolism to underlying health conditions. If you fall in this range, a healthcare professional can help identify the cause and recommend appropriate steps.

Normal weight — BMI 18.5 to 24.9

This range is associated with the lowest risk of weight-related health issues across the general population. Research consistently links a BMI in this range with better cardiovascular outcomes, lower risk of type 2 diabetes, and longer life expectancy. Maintaining this range through regular movement and balanced nutrition is the goal most health guidelines target.

Overweight — BMI 25 to 29.9

A BMI in this range indicates excess weight relative to height, which can increase the risk of cardiovascular disease, high blood pressure, and type 2 diabetes over time. However, context matters — someone with high muscle mass may register here without elevated health risk. Modest increases in daily activity, including walking, have been shown to reduce metabolic risk even without significant weight loss.

Obese — BMI 30 and above

A BMI of 30 or above is associated with significantly elevated risk of serious health conditions including heart disease, stroke, type 2 diabetes, sleep apnea, and certain cancers. The WHO further subdivides this range into Class I (30–34.9), Class II (35–39.9), and Class III (≥40). Lifestyle changes — including increased physical activity and dietary adjustment — are the first-line intervention recommended by most clinical guidelines, with walking being among the most accessible starting points.

Track it with StepGoals

Regular walking is one of the most evidence-backed lifestyle changes for moving toward or maintaining a healthy BMI. Research published in JAMA Internal Medicine found that people who walked more than 7,500 steps per day had significantly lower BMI and body fat percentage than those who walked fewer. StepGoals helps you build that daily walking habit with a step goal calibrated to your current activity level, streak tracking to maintain consistency, and awards that reinforce the behavior over the weeks and months it takes to see change.

Because BMI shifts slowly, consistency over time matters more than any single day's step count. StepGoals' weekly and monthly reports let you monitor your activity trends over time — giving you the long view that short-term tracking often misses.