What is the difference between RMR and BMR?

BMR is measured after an overnight fast, at complete rest, in a temperature-controlled room. RMR uses looser conditions and comes out roughly 5-10% higher. In everyday use the terms are often swapped.

Which equation should I use?

Mifflin-St Jeor is the general-purpose default. If you have a reliable body fat measurement, Katch-McArdle is usually closer because it works from lean mass.

Adding lean mass raises it modestly, since muscle is metabolically active tissue. Claims of large increases from supplements or specific foods are not supported by evidence.

Why does my RMR fall when I diet?

Losing weight reduces both fat and lean tissue, so there is less body mass to maintain. This is expected, and it is one reason calorie targets need revisiting during a diet.

RMR Calculator

Estimate resting metabolic rate with Mifflin-St Jeor, Harris-Benedict and Katch-McArdle.

Enter your details and your result will appear here.

What Is RMR?

Resting metabolic rate (RMR) is the energy your body uses over 24 hours at rest, including digestion and normal daily fluctuation. It is measured under less strict conditions than basal metabolic rate and typically comes out a few percent higher.

Understanding Your RMR Result

RMR covers the cost of keeping you alive: circulation, breathing, cell repair, brain activity and thermoregulation. It usually accounts for 60-75% of total daily energy expenditure, which is why it is the anchor for any calorie target. Lean mass is the strongest predictor, so two people of the same weight can have different rates.

How Is RMR Calculated?

RMR (Mifflin-St Jeor) = 10w + 6.25h - 5a + 5 (male) or -161 (female)

Methodology

Mifflin-St Jeor is used as the default estimate. The revised Harris-Benedict equation (Roza and Shizgal, 1984) is shown for comparison, and Katch-McArdle (370 + 21.6 x lean body mass in kg) is added when you supply a body fat percentage, since it works from lean mass rather than total weight.

Worked Example

A 30-year-old woman who is 5 ft 5 in (165 cm) and 140 lb (63.5 kg) has a Mifflin-St Jeor RMR of about 1,331 calories a day. If she also knows she is 25% body fat, her lean mass is 47.6 kg and Katch-McArdle returns about 1,398 calories.

Important Limitations

Predictive equations sit within roughly 10% of measured values for most healthy adults, and further off for people at the extremes of body composition, older adults and those with metabolic conditions. Only indirect calorimetry measures RMR directly. This tool does not account for illness, medication or pregnancy.

Frequently Asked Questions

What is the difference between RMR and BMR?: BMR is measured after an overnight fast, at complete rest, in a temperature-controlled room. RMR uses looser conditions and comes out roughly 5-10% higher. In everyday use the terms are often swapped.
Which equation should I use?: Mifflin-St Jeor is the general-purpose default. If you have a reliable body fat measurement, Katch-McArdle is usually closer because it works from lean mass.
Can I raise my RMR?: Adding lean mass raises it modestly, since muscle is metabolically active tissue. Claims of large increases from supplements or specific foods are not supported by evidence.
Why does my RMR fall when I diet?: Losing weight reduces both fat and lean tissue, so there is less body mass to maintain. This is expected, and it is one reason calorie targets need revisiting during a diet.