Calories burned by
heart rate calculator

Calories burned during exercise from your average heart rate, bodyweight, sex and age — the Keytel 2005 equation. Imperial or metric, per minute and per session, with the one thing it needs to be read honestly: it only holds for steady aerobic effort.

How the math works

The calculator runs the Keytel et al. (2005) heart-rate energy-expenditure equation — the one most "calories burned by heart rate" tools use, usually without naming it. It regresses energy expenditure on your average heart rate, bodyweight, and age, with separate coefficients for men and women. The result comes out in kilojoules per minute; dividing by 4.184 (the kilojoules in one kilocalorie) gives kcal/min.

Each extra beat per minute adds a fixed amount — 0.6309 kJ/min for men, 0.4472 for women, or about 0.15 and 0.11 kcal/min per bpm. Heart rate and age have no imperial/metric version, so bodyweight is the only input the unit toggle touches; it converts by the exact factor 1 lb = 0.45359237 kg. The weight term is positive for men and negative for women — a feature of the cohort Keytel fitted, not a rule that heavier women spend less — which is exactly why you can't score a man against the women's line or the reverse.

Worked example

A 35-year-old man, 175 lb (79.4 kg), holds an average of 140 bpm through a 45-minute steady aerobic session.

• Energy rate: −55.0969 + 0.6309 × 140 + 0.1988 × 79.4 + 0.2017 × 35 = 56.07 kJ/min
• Per minute: 56.07 ÷ 4.184 = 13.4 kcal/min (804 kcal/h)
• Session (45 min): 603 kcal

Run the identical numbers as a woman and the equation returns 8.3 kcal/min — about 374 kcal over the same 45 minutes, roughly 38% lower. Same heart rate, same weight, same age: the sex you select moves the answer by more than a third, which is the whole reason the coefficients are split. A 42-year-old woman at 130 lb (59.0 kg) averaging 135 bpm for 40 minutes lands at 8.5 kcal/min, about 341 kcal.

When this calculator is wrong

A heart-rate calorie number is only as honest as the straight line it assumes between heart rate and energy, and that line is straight only inside the steady-state aerobic band it was fitted on. Keytel built the equation from submaximal cycling and treadmill stages — 35%, 62% and 80% of VO₂max, in 115 adults aged 18 to 45. Inside that band, heart rate tracks aerobic metabolic rate and the estimate is fair. Outside it, heart rate is pushed up by things that cost little oxygen — isometric tension in a heavy set, heat, dehydration, caffeine, and cardiac drift late in a long effort — so the same heart rate no longer means the same calorie rate, and the number reads high. There's a second discount built in: Keytel published one model with a measured VO₂max (R² = 83.3%) and one without it (R² = 73.4%). You're almost certainly getting the without-VO₂max form, so roughly a quarter of the variance is unexplained before your individual heart-rate economy is even considered.

The counter-case is that within that aerobic band — a tempo run, a bike ride, a rowing piece at a constant pull — and tracked as your own trend under a fixed device and chest-strap placement, a heart-rate estimate still beats a generic MET value, because it responds to your fitness, the heat, and how recovered you are that day.

• Strength work and intervals read high. A circuit or a HIIT session can average a high heart rate on very little aerobic cost; the equation doesn't know the difference and will over-count. For those, a work-based number (or a power meter) is closer to the truth.
• It's calibrated for ages 18–45. That was the cohort. Outside it — and for children or older adults especially — the estimate drifts, and the calculator says so rather than printing a confident figure.
• Wrist optical heart rate is the weak link. The math is only as good as the heart-rate input, and wrist sensors lag and mis-read during intervals and cold starts. A chest strap feeds the equation a better number.

What to do with the result

Use it for steady cardio, read it as a band, and let the scale calibrate it. For a run, ride, or row held at a roughly constant effort, log the session total and treat it as the energy that work added — then over two weeks, compare your weight trend against your intake and the totals you've been logging. If the weight isn't moving the way the numbers predict, adjust your intake by 100–200 kcal rather than trusting the calorie readout; your own trend under a fixed protocol is a better measurement than any single estimate.

For strength sessions and intervals, don't lean on this number — the heart-rate-to-energy line comes apart there. Size those from the work done (sets, load, time) or a power meter, and keep the heart-rate estimate for the aerobic days it was built for. When you do compare sessions, keep the device and strap placement the same each time, so a change in the number means a change in the effort and not in the sensor.

Common questions

How many calories do I burn at a given heart rate?

It depends on your sex, weight and age, not heart rate alone. For a 35-year-old, 175 lb (79.4 kg) man at an average 140 bpm, the Keytel equation gives about 13.4 kcal/min — roughly 603 kcal over 45 minutes. Each extra 10 bpm adds about 1.5 kcal/min for men and 1.1 for women. A woman at the same inputs would be near 8.3 kcal/min, because the coefficients differ by sex.

What formula does a heart rate calorie calculator use?

Almost always the Keytel et al. (2005) regression from the Journal of Sports Sciences, which predicts energy expenditure from heart rate, weight and age, separately for men and women. It comes in two forms — with a measured VO₂max and without — and online tools use the without-VO₂max version, because few people have a lab VO₂max to enter. That version explains about 73% of the variance (R² = 0.734), so it's a good estimate, not a precise count.

Is a heart rate calorie estimate accurate?

For steady aerobic exercise, reasonably — it was validated on submaximal cycling and treadmill work and tracks aerobic effort well there. For resistance training, HIIT, or anything where heart rate is driven up by isometric tension, heat, or dehydration, it reads high, because heart rate and energy come apart outside the steady-state band. And it inherits your wrist or strap's measurement error. Treat it as a band and a trend, not a ledger.

Why do men and women get different calories at the same heart rate?

Because Keytel fitted separate equations for each sex, with different coefficients for heart rate, weight and age — and the weight term is positive for men but negative for women. That's a property of the data the equation was built on, not a claim that one sex "burns more." It does mean you have to enter the right sex: at 140 bpm, 175 lb and 35 years, the male form gives about 13.4 kcal/min and the female form about 8.3.

Can I use my average heart rate from a weights session?

You can enter it, but the number will be too high. The equation assumes heart rate reflects aerobic metabolic rate, which holds for steady cardio but not for lifting, where isometric tension and between-set recovery lift heart rate without a matching oxygen cost. For strength work, estimate from the work done or a MET-based figure instead, and keep the heart-rate method for your aerobic days.

Do I need my VO₂max to use this?

No — the calculator uses the Keytel form that doesn't require it, which is why only sex, weight, age and heart rate are asked. The trade-off is accuracy: the with-VO₂max model explained 83% of the variance in Keytel's data, the without-VO₂max model about 73%. If you have a lab-measured VO₂max, the fuller model is tighter, but for day-to-day planning the simpler form is enough.