Cunningham Equation Calculator

The Cunningham equation was published in 1980 as a method to estimate resting metabolic rate using lean body mass rather than total body weight. The core insight is that metabolically active tissue (muscle, organs) drives resting energy expenditure, while fat tissue is relatively metabolically inactive at rest.

This makes the equation particularly relevant for individuals who know their body composition — whether through body fat percentage estimates, DEXA scans, or other assessment methods.

The original 1980 formula is:

BMR = 500 + (22 × LBM_kg)

In 1991, Cunningham published a revision based on additional validation data:

BMR = 370 + (21.6 × LBM_kg)

The 1991 revision has a lower intercept and a slightly lower coefficient, which generally produces a somewhat lower estimate. This calculator shows both versions so you can see the range between them.

Weight-based equations (like Mifflin-St Jeor or Harris-Benedict) use total body weight, which includes both lean mass and fat mass. For two individuals at the same weight but different body compositions, a weight-based equation will produce identical estimates.

LBM-based equations like Cunningham account for body composition differences. An individual with more lean mass relative to their total weight would receive a higher estimate, reflecting the greater proportion of metabolically active tissue.

The practical limitation is that LBM-based equations require a body composition input, which introduces its own estimation uncertainty depending on the method used to measure body fat percentage.

If you know your body fat percentage, lean body mass is calculated as:

LBM = Weight × (1 − Body Fat % / 100)

Body fat percentage can be estimated through various methods, each with different levels of precision. Common approaches include skinfold calipers, bioelectrical impedance scales, the Navy body fat formula (using waist and neck circumference), and DEXA scans. Each has trade-offs between accessibility and consistency.

BMR represents the energy your body uses at complete rest over 24 hours. Total Daily Energy Expenditure (TDEE) accounts for physical activity by multiplying BMR by an activity factor:

Activity multipliers are broad categories. Most people fall somewhere between levels, so TDEE estimates are best used as a starting reference for personal tracking.

The Katch-McArdle equation (BMR = 370 + 21.6 × LBM) is mathematically identical to the 1991 Cunningham revision. In practice, the terms are often used interchangeably in fitness and nutrition references.

The key distinction is historical: Cunningham published the original LBM-based approach in 1980, then refined it in 1991. McArdle, Katch, and Katch presented the same formula in their widely used textbook "Exercise Physiology: Energy, Nutrition, and Human Performance." This calculator focuses on both Cunningham formula versions, while the Katch-McArdle calculator page explores body fat estimation methods in more depth.