BMR Calculator
Calculate your Basal Metabolic Rate (BMR) — the number of calories your body burns at complete rest. Supports both the Mifflin-St Jeor and revised Harris-Benedict equations in imperial and metric units.
Formulas, assumptions, and rounding are documented in our calculator methodology.
Basal Metabolic Rate (BMR)
1,737
calories/day at complete rest
Mifflin-St Jeor equation
BMR Comparison
- Mifflin-St Jeor (selected)
- 1,737 cal/day
- Harris-Benedict (alternate)
- 1,804 cal/day
- Difference
- 67 cal/day
Mifflin-St Jeor BMR Formula
Men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5. Women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161. Unit conversions: 1 lb = 0.4536 kg; height in cm = (feet × 12 + inches) × 2.54. Example (male, 30 years, 170 lbs, 5'10"): 10 × 77.1 + 6.25 × 177.8 − 5 × 30 + 5 = 771 + 1111.25 − 150 + 5 = 1,737 calories/day.
Harris-Benedict BMR Formula (Revised 1984)
Men: BMR = 88.362 + (13.397 × kg) + (4.799 × cm) − (5.677 × age). Women: BMR = 447.593 + (9.247 × kg) + (3.098 × cm) − (4.33 × age). The original 1919 Harris-Benedict equation tends to overestimate BMR by about 5% for most people. The 1984 revised version by Roza and Shizgal corrected for this and is the standard version used today.
What Affects BMR Beyond Age, Weight, Height, and Sex
Body composition: higher muscle mass increases BMR; higher fat mass decreases it relative to total weight. Hormonal status: thyroid hormones directly regulate metabolic rate — hypothyroidism lowers BMR, hyperthyroidism raises it. Health conditions: fever increases BMR roughly 7% per degree Fahrenheit. Diet: prolonged calorie restriction lowers BMR through metabolic adaptation. Climate: living in very cold or very hot environments can increase BMR slightly. These formulas do not account for any of these factors.
Frequently Asked Questions
- BMR (Basal Metabolic Rate) is the number of calories your body burns in 24 hours while completely at rest — to keep your heart beating, lungs breathing, body temperature regulated, and organs functioning. It does not include any calories burned through movement or digestion.
- The Mifflin-St Jeor equation (1990) is generally considered the most accurate for most adults and is recommended by major dietetic organizations. The revised Harris-Benedict equation (1984) is also widely used and tends to produce slightly higher estimates. Neither accounts for body composition — lean individuals may have higher BMRs than either formula estimates.
- Multiply your BMR by an activity factor: sedentary (desk job, no exercise) × 1.2; lightly active (1–3 days/week) × 1.375; moderately active (3–5 days/week) × 1.55; very active (6–7 days/week) × 1.725; extra active (hard daily training + physical job) × 1.9. This product is your TDEE — Total Daily Energy Expenditure.
- Yes. Muscle tissue is more metabolically active than fat tissue, burning roughly 6 calories per pound per day at rest compared to about 2 calories per pound of fat. Building muscle through strength training gradually increases BMR over time. Standard BMR formulas only use weight, height, age, and sex — they don't distinguish between lean mass and fat mass.
- BMR formulas differ. If the previous calculator used the original 1919 Harris-Benedict equation it will give higher results than the 1984 revised version. If it used the Mifflin-St Jeor equation it should match this calculator closely. Slight differences can also come from unit rounding. The Mifflin-St Jeor equation is the current recommended standard for non-clinical use.