Understanding This Calculator
Resting Metabolic Rate is closely related to BMR but typically measured under slightly less strict conditions, and it’s often estimated using one of two formulas depending on what data you have. Mifflin-St Jeor uses age, height, and weight; Katch-McArdle uses lean body mass directly, which makes it more accurate for people who know their body fat percentage — especially athletes with above-average muscle mass.
If you don’t know your body fat %, leave that field at 0 and the calculator defaults to Mifflin-St Jeor automatically.
- lean mass total weight × (1 − body fat % ÷ 100)
- 370, 21.6 regression constants from the Katch-McArdle study
| Formula | Inputs Needed | Best For |
|---|---|---|
| Mifflin-St Jeor | age, height, weight | General population |
| Katch-McArdle | weight, body fat % | Athletes, known lean mass |
Frequently Asked Questions
Which formula is more accurate?
Katch-McArdle tends to be more accurate for lean, muscular individuals since it’s based directly on metabolically active tissue rather than total body weight, but it requires a reasonably accurate body fat % measurement to be useful.
How is RMR different from BMR?
They’re closely related and often used interchangeably; RMR is typically measured under slightly less controlled conditions (not requiring an overnight lab stay) and tends to run marginally higher than strict BMR.