BMI Calculator
Calculate your Body Mass Index, discover your healthy weight range, and estimate daily maintenance calories without bloated signups or tracking scripts.
Add your age, sex, and activity level to estimate your Basal Metabolic Rate and daily maintenance calorie burn.
How to Use This Calculator
- Select your unit preference: Choose Metric if you know your height in centimeters and weight in kilograms, or US / Imperial for feet, inches, and pounds.
- Enter your height and weight: Type your numbers into the input boxes. The calculator computes your Body Mass Index and healthy weight window on every keystroke.
- Add age, sex, and activity (optional): Entering these personal metrics unlocks your Basal Metabolic Rate and daily maintenance calorie burn right below your BMI card.
- Check your weight targets: Review your distance from the healthy BMI range and inspect customized calorie numbers for maintenance, steady fat loss, or lean gain.
The Formula
Body Mass Index was developed in the 1830s by Belgian statistician Adolphe Quetelet. It measures body mass relative to stature by squaring height in the denominator, accounting for the natural expansion of surface area.
BMI = Weight (kg) / (Height (m))²
Imperial Formula:
BMI = 703 × Weight (lbs) / (Height (inches))²
Mifflin-St Jeor Calorie Equation
To estimate your daily energy requirements, this tool pairs your BMI with the clinically respected Mifflin-St Jeor formula to determine your Basal Metabolic Rate (BMR):
Women: BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age in years) - 161
TDEE: Daily Maintenance Calories = BMR × Activity Multiplier (1.2 to 1.9)
Example
Let's run a realistic walkthrough for someone standing 175 cm tall (5 ft 9 in) and weighing 70 kg (about 154.3 lbs), who is 30 years old with moderate gym workouts.
Height = 175 cm ÷ 100 = 1.75 m
Step 2: Square the height
1.75 × 1.75 = 3.0625 m²
Step 3: Divide weight by squared height
BMI = 70 ÷ 3.0625 = 22.86 (displays as 22.9)
Step 4: Check WHO category & healthy boundaries
Because 22.9 falls between 18.5 and 24.9, the result is Normal Weight.
Healthy weight range for 175 cm = 18.5 × 3.0625 to 24.9 × 3.0625 = 56.7 kg to 76.3 kg.
Step 5: Compute BMR and Daily Calories (Male, 30y, Moderate Activity 1.55)
BMR = (10 × 70) + (6.25 × 175) - (5 × 30) + 5 = 700 + 1093.75 - 150 + 5 = 1649 kcal
Maintenance TDEE = 1648.75 × 1.55 = 2556 calories/day.
With an active lifestyle and balanced diet, consuming about 2,556 calories per day keeps this weight steady, while an intake of 2,056 calories per day supports steady fat loss of approximately half a kilo per week.
Why We Built This Without the Clutter
Sitting at an office desk all week sneaks up on you. During our workplace health checkup last month, stepping onto the clinic scale gave me an honest wake-up call about how little I was moving during long desk shifts. I'd spent months barely getting four thousand steps a day.
I don't obsess over decimal points on a scale. How my work shirts fit around the waist and whether I feel sluggish after lunch matter way more to me than a single math ratio. The number is a practical guardrail to keep me honest, but day-to-day stamina tells the real story.
I got fed up with mainstream health and diet portals that hit you with four interstitial ads, demand an email signup before showing a single decimal, and lock basic calorie projections behind paid subscriptions. Your body measurements are personal. That is why this calculator runs all math directly in your browser without sending a single byte over the web.
Frequently Asked Questions
Body Mass Index is a simple screening ratio that divides your weight by your height squared. It gives doctors and health organizations a quick, standardized way to spot whether someone falls into an underweight, normal, overweight, or obese weight class.
The World Health Organization defines a normal, healthy adult BMI between 18.5 and 24.9. A score below 18.5 indicates underweight, 25.0 to 29.9 is overweight, and 30.0 or higher falls into the obesity categories.
BMI cannot distinguish between lean muscle and body fat. Dense muscle weighs more by volume than fat tissue, meaning athletes and heavy lifters often register as overweight or obese despite having lean frames and low body fat.
When you enter your age and sex, the tool applies the Mifflin-St Jeor equation to find your Basal Metabolic Rate. Multiplying that baseline by your activity level reveals your Total Daily Energy Expenditure (TDEE), showing how many calories you burn each day.
A standard deficit or surplus of 500 calories per day creates roughly a 3,500 calorie difference each week, translating to about 0.5 kg (or 1 pound) of gradual weight change. Steady, smaller adjustments are much easier to stick with long-term than crash diets.