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Resting Metabolic Rate (Cunningham) Calculator

Enter weight and body fat percentage to estimate RMR with the Cunningham equation.

How it is calculated

The tool first strips out fat: LBM = weight × (1 − body fat % ÷ 100), with weight in kilograms and body fat as a percentage. Resting metabolic rate then follows the Cunningham line: RMR = 500 + 22 × LBM, in kcal per day. Two ready-made daily totals are shown by multiplying RMR by a fixed activity factor: × 1.2 for a sedentary day and × 1.55 for an active one. Results are rounded to whole kcal, and lean mass to two decimals. Weight must be above zero and body fat must be 0 or more but below 100, otherwise no result appears. The equation uses only lean mass, so age and sex do not matter, and the answer is only as good as the body fat figure you enter. It estimates energy at rest; real needs also depend on training and daily movement.

Worked example

An 80 kg person with 15% body fat. Lean body mass: 80 × (1 − 0.15) = 68.00 kg. RMR = 500 + 22 × 68 = 500 + 1,496 = 1,996 kcal/day. Sedentary: 1,996 × 1.2 = 2,395 kcal/day. Active: 1,996 × 1.55 = 3,094 kcal/day. If the same person were 25% fat, lean mass would drop to 60.00 kg and RMR to 1,820 kcal/day.

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Common mistakes

  • Entering body fat as a decimal (0.15) instead of a percentage (15). The tool accepts it, sees almost 100% lean mass and gives 2,257 kcal/day instead of 1,996, overstating RMR by hundreds of kcal.
  • Using the sedentary or active totals as a fat-loss target without subtracting a deficit; they are maintenance-style figures, not a diet.
  • Taking a body fat reading from a scale that fluctuates with hydration, since each point of fat moves RMR by about 18 kcal at this weight.
  • Typing weight in pounds into the kilogram field. 176 lb entered as 176 gives an RMR of 3,791 kcal/day, far above the real figure.
  • Using the Cunningham result for someone with no reliable body fat measurement; the whole benefit of the formula depends on that input.

Sources

About this calculator

The Cunningham equation, developed by John Cunningham in 1980, estimates resting metabolic rate (RMR) directly from lean body mass (LBM) rather than total body weight: RMR = 500 + 22 × LBM (kg). Because metabolically active lean tissue — not fat — drives the vast majority of resting energy expenditure, formulas built on LBM tend to be more accurate than weight-based equations like Harris-Benedict or Mifflin-St Jeor for people whose body composition differs substantially from average.

Sports dietitians, strength coaches, and lean or muscular athletes with a known body fat percentage (from DXA, skinfolds, or bioelectrical impedance) favor the Cunningham equation over general-population formulas, since a heavily muscled athlete's RMR is systematically underestimated by weight-only equations that don't distinguish muscle from fat.

Your body weight and body fat percentage are used to derive your lean body mass, and the Cunningham equation is then applied to that figure to estimate your resting metabolic rate.

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