About calories burned by heart rate
Heart rate is one of the most practical ways to estimate calorie burn because it tracks how hard your cardiovascular system is working. During steady aerobic exercise, oxygen uptake (VO2) rises roughly in proportion to heart rate, and each liter of oxygen consumed burns about 5 kcal. Since we can measure heart rate cheaply and continuously with a chest strap or optical wrist sensor — but cannot easily measure VO2 outside a lab — researchers built regression models that predict energy expenditure from heart rate plus a few personal variables. This calculator uses the most widely cited of those models.
The formula (Keytel et al., 2005)
This tool implements the sex-specific equations published by Keytel and colleagues in the Journal of Sports Sciences (2005), derived from 115 participants during graded exercise with simultaneous VO2 measurement. They give energy expenditure in kilojoules per minute (kJ/min), which we convert to kilocalories by dividing by 4.184:
- Men: EE (kJ/min) = −55.0969 + (0.6309 × HR) + (0.1988 × W) + (0.2017 × A)
- Women: EE (kJ/min) = −20.4022 + (0.4472 × HR) − (0.1263 × W) + (0.0740 × A)
where HR is average heart rate in beats per minute, W is body weight in kilograms, and A is age in years. Total calories = (kJ/min ÷ 4.184) × exercise duration in minutes. If you enter weight in pounds, the calculator converts it to kilograms first (1 kg ≈ 2.2046 lb).
Why age, weight, and sex matter
- Weight: heavier bodies require more energy to move and to circulate blood, so the men's equation adds calories as weight rises. (The women's equation carries a small negative weight coefficient — an artifact of that specific regression, not a claim that heavier women burn fewer calories in general.)
- Age: maximum heart rate declines with age, so a given heart rate represents a higher relative effort in an older person; the model adjusts for this.
- Sex: men and women differ in average body composition, blood volume, and cardiac output, so Keytel fit entirely separate coefficients for each.
Typical burn-rate reference points
For a moderately active adult, these equations produce roughly:
- Light cardio (~110 bpm): about 6–9 kcal/min, or ~360–540 kcal/hour.
- Moderate cardio (~140 bpm): about 10–14 kcal/min, or ~600–840 kcal/hour.
- Hard cardio (~165 bpm): about 14–18 kcal/min, or ~840–1,080 kcal/hour.
Example: an 80 kg, 35-year-old man exercising at 140 bpm for 45 minutes burns about (−55.0969 + 0.6309×140 + 0.1988×80 + 0.2017×35) ÷ 4.184 ≈ 13.4 kcal/min × 45 ≈ 604 kcal.