Basal Metabolic Rate (BMR) Calculator
This tool estimates Basal Metabolic Rate (BMR) — the calories your body requires at rest to maintain basic physiological functions. It offers multiple validated equations so you can compare estimates and choose the one most appropriate for your situation.
Use SI inputs (kg and cm) or imperial inputs (lb and ft+in). For the lean-mass method (Katch–McArdle), provide an objective body fat percentage for best accuracy. All outputs are presented as kcal/day and include typical activity multipliers for estimated daily energy expenditure (TDEE).
Modern widely recommended equation for estimating resting energy expenditure using weight, height, age, and sex.
Inputs
Results
BMR (Mifflin–St Jeor)
1,483
Estimated Daily Calories — Sedentary
1,779
Estimated Daily Calories — Lightly active
2,039
Estimated Daily Calories — Moderately active
2,298
Estimated Daily Calories — Very active
2,558
Estimated Daily Calories — Extra active
2,817
| Output | Value | Unit |
|---|---|---|
| BMR (Mifflin–St Jeor) | 1,483 | kcal/day |
| Estimated Daily Calories — Sedentary | 1,779 | kcal/day |
| Estimated Daily Calories — Lightly active | 2,039 | kcal/day |
| Estimated Daily Calories — Moderately active | 2,298 | kcal/day |
| Estimated Daily Calories — Very active | 2,558 | kcal/day |
| Estimated Daily Calories — Extra active | 2,817 | kcal/day |
Visualization
Methodology
Three established formulas are implemented: Mifflin–St Jeor, Revised Harris–Benedict, and Katch–McArdle. Each uses different predictors (mass/height/age/sex or lean mass) and yields slightly different estimates.
Unit handling: if both metric and imperial fields are provided, metric fields are used for calculation. Imperial inputs are converted to metric using exact conversion factors: 1 lb = 0.45359237 kg and 1 in = 2.54 cm.
Quality and safety: numeric inputs are validated with sensible limits. Results include clear caveats about measurement uncertainty and are intended for informational and planning purposes, not for clinical diagnosis.
Worked examples
Example: 70 kg, 175 cm, 30 years, male gives different BMRs: Mifflin–St Jeor typically near 1665 kcal/day; Harris–Benedict may differ by a few percent; Katch–McArdle depends on body fat used to compute lean mass.
If you only have imperial inputs, enter weight in lb and height in ft+in; the tool converts to metric before applying formulas.
Key takeaways
Choose Mifflin–St Jeor for a general-purpose estimate, Revised Harris–Benedict for historical comparison, and Katch–McArdle when an accurate body fat percentage is available.
Treat outputs as model estimates. Use measured resting metabolic rate from indirect calorimetry if clinical precision is required.
Further resources
Expert Q&A
How accurate are these estimates?
These equations provide population-level estimates and may vary from measured resting metabolic rate by 5–15% or more depending on individual factors. Accuracy depends on input precision (weight, height, age, body fat) and biological variability.
Which method should I use?
Use Mifflin–St Jeor for most adults. Use Katch–McArdle when you have a reliable body fat percentage; it can be more accurate for athletic or low-body-fat individuals. Compare across methods to understand the estimate range.
Can I use this for clinical decisions or medical dosing?
No. This calculator is for informational and planning purposes only. For clinical or dosing decisions, rely on direct measurement and professional medical guidance.
What are the main sources of error?
Measurement error in weight/height/body fat, inappropriate equation choice for an individual's physiology, and activity multiplier selection for TDEE introduce the largest uncertainties.
How does the tool manage units?
If metric fields (weight_kg or height_cm) are supplied and greater than zero they are used. If metric fields are empty or zero, the tool converts imperial inputs (weight_lb, height_ft + height_in) to metric using exact conversion constants.
Are these results compliant with any standards?
This tool follows recognized software and measurement guidance for traceability and user-facing accuracy statements. See citations for standards and guidance on software quality, measurement uncertainty, and workplace safety.
Sources & citations
- National Institute of Standards and Technology (NIST) — Software and measurement guidance — https://www.nist.gov
- International Organization for Standardization (ISO) — Standards on measurement and uncertainty — https://www.iso.org
- Institute of Electrical and Electronics Engineers (IEEE) — Software engineering and quality guidance — https://www.ieee.org
- Occupational Safety and Health Administration (OSHA) — Guidance on measurement and workplace safety — https://www.osha.gov
- PubMed/NIH — Research literature on resting metabolic rate and predictive equations — https://pubmed.ncbi.nlm.nih.gov