Last updated July 2026. This page explains exactly how the numbers on this site are calculated, what formulas we use, and where those formulas come from, so you’re never relying on a black box.
Why This Page Exists
Most calorie calculators online don’t tell you what’s happening under the hood. You put in your weight and speed, a number comes out, and you’re supposed to trust it. We think that’s backwards. Every number on this site comes from a documented, publicly available formula used in exercise science, not a proprietary black-box algorithm. This page shows the actual math.
The Core Formula
Every calorie estimate on this site starts from the same base equation used in clinical and research exercise physiology:
Calories (kcal) = MET × Weight (kg) × Duration (hours)
MET stands for Metabolic Equivalent of Task. It’s a ratio: how many times harder your body is working compared to sitting quietly at rest, which is defined as 1 MET, roughly 3.5 ml of oxygen consumed per kilogram of body weight per minute. A 6 MET activity burns six times the energy of sitting still, for the same body weight and time.
How We Calculate MET for Your Session
Walking and running have different metabolic costs at the same speed, so treadmill calculators need two different equations, not one. We use the metabolic equations published by the American College of Sports Medicine (ACSM) in its Guidelines for Exercise Testing and Prescription. Both equations take your speed (converted to meters per minute) and incline (as a decimal grade) and return your oxygen consumption, VO2, in ml/kg/min. We then divide by 3.5 to get your MET value.
Walking Equation (used under 5 mph / 8 km/h)
VO2 = (0.1 × Speed) + (1.8 × Speed × Grade) + 3.5
Running Equation (used at 5 mph / 8 km/h and above)
VO2 = (0.2 × Speed) + (0.9 × Speed × Grade) + 3.5
Speed is in meters per minute in both equations. Grade is your incline percentage expressed as a decimal, so a 5% incline is entered as 0.05. The two equations diverge because running and walking use different biomechanics, running has an airborne phase and a steeper energy cost curve as speed increases, which is why a single formula across all speeds would misrepresent one or the other.
We use 5 mph (roughly 8 km/h) as the walking-to-running cutoff. This is a simplification, real gait transition speed varies by individual, stride length, and incline, but it’s a standard, defensible threshold used across exercise physiology literature and by our calculators for consistency.
Unit Conversions We Use
| Conversion | Factor |
|---|---|
| Pounds to kilograms | divide by 2.20462 |
| Miles per hour to km/h | multiply by 1.60934 |
| km/h to meters per minute | multiply by 1000, divide by 60 |
| Incline percent to decimal grade | divide by 100 |
| Incline percent to angle (degrees) | arctangent (grade ÷ 100) |
Why We Don’t Use a Flat MET Lookup Table
A lot of calculators use a static table: pick your activity from a dropdown, get a fixed MET value. That works for something like typing (yes, that’s an activity in the Compendium of Physical Activities), because a MET table look-up is fine when speed and incline are irrelevant. It falls apart for a treadmill, where your calorie burn changes continuously with speed and incline. We calculate MET dynamically for your exact inputs instead of rounding you into the nearest table bucket.
What This Methodology Does Not Account For
Being transparent about the formula also means being transparent about its limits. None of the following are captured by a weight-speed-incline MET calculation, and no online calculator, including this one, fully corrects for them:
- Body composition. Two people at the same weight with different muscle-to-fat ratios burn different amounts of energy for the same activity. MET-based formulas use body weight as a proxy for this, not a precise measure of it.
- Age and sex. Metabolic rate shifts with age and differs by sex on average. The base ACSM equations do not adjust for either.
- Fitness level and movement economy. A trained runner is typically more efficient at a given pace than an untrained one, meaning they burn somewhat less energy to cover the same distance at the same speed.
- Handrail use. Holding the rails offloads real body weight from your legs. No formula, including ours, can detect or correct for this. If you’re gripping the rails, treat the number as an overestimate.
- Environmental factors. Heat, humidity, and hydration status affect real energy expenditure and are not part of the MET calculation.
This is why we recommend using this calculator (or any calculator) for consistent, relative tracking rather than treating any single number as a lab-verified fact. The same method, applied the same way every session, gives you a meaningful trend even when the absolute number carries some margin of error.
On the Accuracy Research We Cite
Elsewhere on this site we reference independent testing from UC San Francisco’s Human Performance Center, which found treadmill consoles overestimate calorie burn by roughly 13% on average compared to lab measurement, with cardio machines overestimating by about 19% on average overall and ellipticals running over 40% high. We cite this to explain why console numbers and calculator numbers, including ours, often disagree with each other and with wearable devices. No calculation method, including the ACSM-based one used on this site, is a substitute for laboratory indirect calorimetry, which remains the gold standard and isn’t practical for everyday use.
Sources & References
- American College of Sports Medicine. ACSM’s Guidelines for Exercise Testing and Prescription, 11th Edition, Wolters Kluwer.
- Ainsworth, B.E. et al. Compendium of Physical Activities: a reference database of MET values for physical activities.
- UC San Francisco Human Performance Center, independent testing of cardio equipment calorie accuracy (as reported by Salon and ABC News/Good Morning America).
Have a question about how a specific number on this site was calculated? Reach out through our contact page and we’ll walk you through the exact math for your case.