Why is calorie burn only an estimate?

Because calorie burn depends on body size, efficiency, effort, terrain, and movement style. Any calculator is giving you a useful range, not a lab reading.

Why do wearables and calculators disagree?

They use different models and different signals. The useful move is to look for a consistent range instead of chasing a single exact number.

Should I eat back every calorie this shows?

Usually not. Most people do better treating exercise calories cautiously, then adjusting from bodyweight and recovery data over time.

What makes the estimate more useful?

Using realistic duration and effort, then comparing multiple sessions so you understand relative output instead of obsessing over one workout.

Is this tool free and private to use?

Yes. AI Fit Hub tools are free, no-signup browser tools. Inputs stay in your browser unless you choose to share a URL.

Do these tools replace medical guidance?

No. These outputs are general fitness estimates — not medical advice.

Methodology: Calories Burned Calculator

Scope

Generic MET-based calorie estimator for any activity in the Compendium of Physical Activities.

Formula

kcal = MET * weight_kg * duration_h.

Coefficients

Parameter	Value	Note
Range	`1.0 – 23.0 MET`

Data sources

Ainsworth BE, Haskell WL, Herrmann SD, et al. 2011 Compendium of Physical Activities. Med Sci Sports Exerc. 2011;43(8):1575-1581. — PMID 21681120. Source of all MET values used in the tool.
Compendium of Physical Activities — online tables (Arizona State University). — Public MET table hosted by the Compendium authors.

Assumptions

Activity intensity matches the selected MET value.

Approximation range

Individual variance around the MET table is typically +/- 10–15%.

Limitations

MET tables do not model fitness level, so the same workout returns the same kcal for a beginner and an elite athlete.

Reproducibility

Running 6 mph (10 MET), 70 kg, 30 min: kcal = 10 * 70 * 0.5 = 350 kcal.

Change log

2026-04-24: methodology page first published.

Running Pace Calculator — Calculate pace per km and mile and project race finish times from one run.
VO2 Max Estimator — Estimate aerobic capacity with the Cooper 12-minute run or Rockport 1-mile walk field tests.
Walking Calorie Calculator — Estimate calories burned from walking using speed, duration, body weight, and incline.
Resting Heart Rate Calculator — Assess cardiovascular fitness from your resting heart rate — classification, cardio age, and improvement targets.

Worked example

Computed by the same engine bundle served at /engines/calories-burned-calculator.js. Re-runnable: the values below are the literal output of compute(engineInput).

Input

tool: calories_burned
weight_kg: 78
duration_minutes: 45
activity_met: 7.5
incline_percent: 0

Output

primaryLabel: Estimated calories burned
primaryValue: 460.69
primaryFormat: calories
summary: MET-based estimate with optional incline multiplier.
metrics: [{"label":"Calories per hour","value":614.25,"format":"calories"},{"label":"MET used","value":7.5,"format":"number"},{"label":"Calories per kg","value":5.91,"format":"number"},{"label":"Incline","value":0,"format":"percent"}]
warnings: []
assumptionsEcho: {"weight_kg":78,"duration_minutes":45,"activity_met":7.5,"incline_percent":0}

FAQ

Why is calorie burn only an estimate?: Because calorie burn depends on body size, efficiency, effort, terrain, and movement style. Any calculator is giving you a useful range, not a lab reading.
Why do wearables and calculators disagree?: They use different models and different signals. The useful move is to look for a consistent range instead of chasing a single exact number.
Should I eat back every calorie this shows?: Usually not. Most people do better treating exercise calories cautiously, then adjusting from bodyweight and recovery data over time.
What makes the estimate more useful?: Using realistic duration and effort, then comparing multiple sessions so you understand relative output instead of obsessing over one workout.
Is this tool free and private to use?: Yes. AI Fit Hub tools are free, no-signup browser tools. Inputs stay in your browser unless you choose to share a URL.
Do these tools replace medical guidance?: No. These outputs are general fitness estimates — not medical advice.