Resting Metabolic Rate (RMR) Calculator – Understand Your Daily Energy Burn at Rest
Resting metabolic rate (RMR) represents the number of calories your body burns at rest to keep you alive and functioning. It includes energy used for breathing, organ function, circulation, and maintaining body temperature. Knowing your RMR is one of the most important starting points for building a nutrition plan, setting calorie targets, and understanding why your body weight changes over time.
This RMR Calculator uses well-known formulas such as Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle to estimate your resting calorie burn and then helps convert it into practical daily calorie needs based on activity level.
How This RMR Calculator Works
This tool provides four modes that focus on different ways to estimate metabolic rate and daily energy needs:
- Mifflin-St Jeor: A modern formula often considered one of the most accurate for the general population.
- Harris-Benedict: A classic formula still widely used in nutrition and clinical settings.
- Katch-McArdle: A formula that uses lean body mass and is ideal if you know your body fat percentage.
- Daily Calorie Needs: Uses RMR plus activity level to estimate how many calories you need per day to maintain, lose, or gain weight.
Mifflin-St Jeor Formula
The Mifflin-St Jeor equation is popular in dietetics and weight management programs because it tends to give realistic estimates for modern lifestyles.
For women: RMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) − 161
This formula uses your body size and age to estimate how many calories you burn at rest. The calculator also derives RMR per hour and per kilogram of body weight, so you can see how your metabolism compares on a relative basis.
Harris-Benedict Formula
The Harris-Benedict equation is one of the earliest metabolic formulas and remains widely used in clinical nutrition, especially when combined with activity factors.
For women: RMR = 447.593 + 9.247 × weight (kg) + 3.098 × height (cm) − 4.330 × age (years)
While it can slightly overestimate or underestimate for certain individuals, it is still very useful for trend analysis and planning calorie intake over time.
Katch-McArdle Formula (Lean Body Mass)
Katch-McArdle is particularly helpful if you know your body fat percentage because it focuses on lean body mass (LBM), which is the primary driver of metabolic rate.
RMR = 370 + 21.6 × Lean Body Mass (kg)
Two people of the same body weight can have very different RMR values if one carries more muscle and less fat. This formula allows a more athlete-focused estimate.
Daily Calorie Needs Based on Activity
RMR tells you how many calories you burn at rest, but in real life you walk, train, work, and move throughout the day. To estimate total daily energy expenditure, the calculator multiplies your RMR by an activity factor.
Common activity factors include:
- Sedentary (little or 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 (intense training): 1.9
The calculator then estimates maintenance calories, a typical weight loss target (about 500 kcal below maintenance), and a weight gain target (about 500 kcal above maintenance).
How to Use This RMR Calculator Effectively
- Start with the Mifflin-St Jeor tab for a solid general estimate of your RMR.
- Compare with Harris-Benedict to see how much the different formulas vary for your body data.
- If you track your body composition, use the Katch-McArdle tab to get an RMR estimate focused on lean mass.
- Switch to the Daily Calorie Needs tab and select your activity level to see how many calories you likely need per day.
- Use the weight loss and weight gain suggestions as starting points rather than strict prescriptions.
RMR vs BMR vs TDEE
It is easy to get confused between RMR, BMR, and TDEE:
- BMR (Basal Metabolic Rate): Calories burned in a lab setting under very strict rest conditions.
- RMR (Resting Metabolic Rate): A practical version of BMR measured at rest, usually slightly higher.
- TDEE (Total Daily Energy Expenditure): RMR plus all daily activity and exercise.
This calculator focuses on RMR, then uses it as the foundation to estimate TDEE. It can be used alongside other tools for a complete health and fitness strategy.
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RMR Calculator FAQs
Frequently Asked Questions About Resting Metabolic Rate
Get quick answers about how RMR works, how to interpret your results, and how to use RMR for nutrition planning.
No. RMR only covers calories burned at rest. Your total daily burn (TDEE) includes RMR plus physical activity, work, training, and other movement. The Daily Needs tab helps bridge that gap.
RMR formulas provide estimates based on population averages. They are useful for planning and tracking trends, but small differences from your true metabolic rate are normal.
Both are widely used. Many modern nutrition programs prefer Mifflin-St Jeor, while Harris-Benedict remains common in medical and clinical environments. Comparing both can give you a reasonable range.
Strength training that builds or maintains muscle mass can increase or preserve RMR. Regular cardio supports heart health but has a smaller direct effect on resting metabolism compared to muscle mass changes.
Recalculate RMR after meaningful changes such as a significant weight change, aging by a few years, or major changes in body composition. For most people, updating every few months is enough.