RMR vs BMR at a glance
| BMR | RMR | |
|---|---|---|
| Measured | On waking, fasted about 12 hours, lying still | At rest, with less strict timing and fasting |
| Typical size | The lower of the two | Usually slightly higher |
| Common use | Research and textbook definitions | Clinics, gyms and most calculators |
The small gap between them matters less than it sounds. Prediction equations themselves can be off by 10% or more for an individual, which is bigger than the typical difference between BMR and RMR.
Why this page uses Mifflin-St Jeor
Mifflin and colleagues published their equation in 1990 after measuring resting energy expenditure in 498 healthy men and women aged 19 to 78, including people with obesity. Because their measurements were resting rather than strictly basal, the equation is a natural RMR estimator. A 2005 systematic review for the American Dietetic Association found it predicted resting rate within 10% of measured values more often than the other equations it compared.
If you have had your RMR measured, that measured number is better than any formula. Multiply it by the activity factor that fits your week to estimate your daily calories.
Turning RMR into daily needs
The calculator shows your RMR as the headline and your TDEE beside it. The activity table converts the same RMR into five daily totals. If you have a measured RMR, multiply it by the same factors yourself: ×1.2 for mostly sitting, up to ×1.9 for very hard daily training.
Frequently asked questions
Is RMR the same as BMR?
They are close but not identical. BMR is measured under strict conditions: after a night’s sleep, about 12 hours without food, lying still in a comfortable room. RMR (resting metabolic rate) is measured at rest with looser rules, so it usually comes out slightly higher. Most calculators, including this one, use the terms almost interchangeably.
Which equation estimates RMR?
The Mifflin-St Jeor equation was built from measured resting energy expenditure (essentially RMR) in 498 healthy adults, so its output is an RMR estimate. The Harris-Benedict equations came from basal measurements. In everyday use the difference is smaller than the error of any equation.
How is RMR measured?
With indirect calorimetry: you breathe into a mouthpiece or under a hood for a short period while resting, and the device works out energy use from oxygen consumed and carbon dioxide produced. Clinics, hospitals and some gyms offer this test.
What should I do with my RMR?
Use it as the base for your daily needs. Multiply by an activity factor (the table in the calculator does this) to get your TDEE, which is the number that relates to how much you eat. RMR on its own is not an eating target.