BMR Calculator

Basal metabolic rate (BMR) is the energy your body uses at complete rest. With the Mifflin-St Jeor equation, a 30-year-old woman who is 5 ft 4 in (162.56 cm) and weighs 140 lb (63.5 kg) has a BMR of 10 × 63.5 + 6.25 × 162.56 − 5 × 30 − 161 ≈ 1,340 calories a day. The BMR calculator below compares three equations.

How to use the BMR calculator

1. Pick an equation. Mifflin-St Jeor is the default; Katch-McArdle needs your body fat percentage.
2. Choose US or metric units and calories or kilojoules.
3. Enter sex, age, height and weight, and body fat if you know it.
4. Read your BMR, then the chart of BMR by age for your measurements and the side-by-side comparison of the equations.
5. Open Show steps for the working with your numbers, or copy the result.

Results are estimates for healthy adults, not medical advice. A doctor or registered dietitian can measure or interpret your energy needs.

What is basal metabolic rate?

The National Academies’ Dietary Reference Intakes for Energy (2023) separate two closely related measures:

The two numbers are very close, and the equations below were fitted to resting measurements, so calculators use the terms almost interchangeably.

How much of your daily energy is BMR?

According to the same report, resting energy expenditure typically accounts for 60 to 70% of total daily energy expenditure, and digesting food (the thermic effect of food) for about 10%. The rest is movement and exercise. Fat-free mass, meaning muscle, organs and bone, is the strongest predictor of resting expenditure: it explains 60 to 80% of the differences between people. When body size and composition are taken into account, sex has little effect, which is why men’s higher average BMR mostly reflects larger bodies and more lean mass.

BMR formulas: Mifflin-St Jeor, Harris-Benedict and Katch-McArdle

W is weight in kilograms, H is height in centimeters and A is age in years. To convert, 1 lb = 0.45359237 kg and 1 in = 2.54 cm.

How the equations differ

• Mifflin-St Jeor was fitted to resting measurements of 498 healthy adults aged 19 to 78, both normal weight and with obesity. The paper also gives one combined equation, 9.99W + 6.25H − 4.92A + 166 × sex − 161 (sex = 1 for men, 0 for women), which the simplified versions above round off. In that study the original 1919 Harris-Benedict equation overestimated measured resting needs by about 5%.
• Revised Harris-Benedict is Roza and Shizgal’s 1984 re-fit of the original data. They reported that it predicts resting needs in healthy people to within about ±14%. For most people it gives a slightly higher number than Mifflin-St Jeor.
• Katch-McArdle uses only lean body mass, so sex, age and height drop out. It fits the finding that fat-free mass drives BMR, but it is only as good as your body fat estimate.

Worked BMR examples

Example 1: Mifflin-St Jeor, US units

The woman from the opening is 30, 5 ft 4 in and 140 lb. Convert: 140 × 0.45359237 ≈ 63.50 kg, and 64 in × 2.54 = 162.56 cm. Then 10 × 63.50 + 6.25 × 162.56 − 5 × 30 − 161 ≈ 635.0 + 1,016.0 − 150 − 161 ≈ 1,340 calories a day, or about 1,340 ÷ 24 ≈ 56 calories an hour.

Example 2: the same woman with revised Harris-Benedict

447.593 + 9.247 × 63.50 + 3.098 × 162.56 − 4.330 × 30 ≈ 447.6 + 587.2 + 503.6 − 129.9 ≈ 1,409 calories a day. That is 69 calories, or about 5%, above Mifflin-St Jeor.

Example 3: Katch-McArdle with body fat

If she has 30% body fat, her lean body mass is 63.50 × 0.70 ≈ 44.45 kg. BMR = 370 + 21.6 × 44.45 ≈ 370 + 960.2 ≈ 1,330 calories a day.

Example 4: a man in metric units and kilojoules

A 40-year-old man is 180 cm and 85 kg. Mifflin-St Jeor: 10 × 85 + 6.25 × 180 − 5 × 40 + 5 = 850 + 1,125 − 200 + 5 = 1,780 calories a day. In kilojoules, 1,780 × 4.184 ≈ 7,448 kJ. Revised Harris-Benedict gives 88.362 + 1,138.745 + 863.82 − 227.08 ≈ 1,864 calories.

BMR by age chart

The equations subtract a fixed amount for each year of age. For the woman in Example 1 (5 ft 4 in, 140 lb), keeping height and weight the same:

Mifflin-St Jeor drops by 50 calories a decade for everyone; revised Harris-Benedict drops by about 43 for women and 57 for men. Measured data tell a slightly different story. The National Academies report that basal expenditure adjusted for body size stays fairly stable from about age 20 to 60 and declines in older adults. The straight lines are averages, not a rule about your own metabolism. The calculator draws this chart for your own numbers.

BMR in kilojoules and per hour

Food labels in many countries use kilojoules. One food calorie (kcal) is 4.184 kJ, so multiply calories by 4.184: 1,340 kcal ≈ 5,607 kJ. To see the rate at any moment, divide by 24: a BMR of 1,340 kcal a day is about 56 kcal an hour.

From BMR to TDEE

BMR is only the resting part of your day. Total daily energy expenditure (TDEE) is usually estimated by multiplying BMR by an activity factor, from about 1.2 for a mostly seated day upward. Because resting expenditure is 60 to 70% of the total, a BMR of 1,340 suggests a daily total somewhere near 1,340 ÷ 0.7 ≈ 1,910 to 1,340 ÷ 0.6 ≈ 2,230 calories. For a figure tied to your activity level, use the TDEE calculator; for weight-goal targets, use the calorie calculator.

Common BMR calculation mistakes

• Using pounds and inches in the equations. They need kilograms and centimeters. Using 140 for weight instead of 63.5 adds 765 calories in Mifflin-St Jeor.
• Using the men’s constant for women. In Mifflin-St Jeor, +5 versus −161 is a 166-calorie difference.
• Treating BMR as a calorie target. BMR is energy at rest, not what you burn in a normal day.
• Total weight in Katch-McArdle. It uses lean body mass, not total weight.

Sources

Checked November 2026.

• National Academies of Sciences, Engineering, and Medicine. Dietary Reference Intakes for Energy (2023), Chapter 4: Factors Affecting Energy Expenditure and Requirements
• Mifflin MD, St Jeor ST et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241-247
• Roza AM, Shizgal HM. The Harris Benedict equation reevaluated. Am J Clin Nutr. 1984;40(1):168-182
• Pavlidou E et al. Revised Harris-Benedict Equation: New Human Resting Metabolic Rate Equation. Metabolites. 2023;13(2):189 (coefficient table)
• Tang M et al. Frontiers in Nutrition. 2025;12:1543263 (Katch-McArdle equation)

BMR practice quiz: 10 questions

Test yourself with 10 multiple-choice questions. Choose an answer and press Submit to see if you are right and why. Your score appears at the end.

Frequently asked questions

What is a normal BMR?

There is no single normal value, because BMR scales with body size and lean mass. The equations give about 1,340 calories a day for a 30-year-old woman who is 5 ft 4 in and 140 lb, and 1,780 for a 40-year-old man who is 180 cm and 85 kg.

Is BMR the same as RMR?

Almost. BMR is measured under stricter conditions (just after waking, 12 or more hours after eating), while RMR allows a few hours since the last meal. The numbers are close, and the equations here estimate resting expenditure.

Does BMR go down with age?

The equations lower it a little each year. Measured data in the National Academies report show size-adjusted basal expenditure staying fairly stable from about 20 to 60 and declining after that.

Why do men usually have a higher BMR?

Mostly because of body size and composition. On average men are larger and carry more fat-free mass, the strongest predictor of resting expenditure. When those are accounted for, the National Academies found that sex has little impact.

How accurate is a BMR calculator?

It predicts the average for people like you. Roza and Shizgal reported about ±14% accuracy for revised Harris-Benedict in healthy people. Only a lab measurement, such as indirect calorimetry, gives your actual BMR.

Related calculators

• TDEE calculator
• Calorie calculator
• BMI calculator
• Ideal weight calculator
• Body fat calculator