About RunKcal
A free, transparent running calorie calculator — and an honest explanation of how the numbers are produced.
RunKcal exists because most calorie estimates on the internet are presented without any explanation of where they come from. A website tells you a 5K burns 400 calories, and you have no way to judge whether that figure applies to you, how it was derived, or how much error is baked into it.
This site takes the opposite approach. Every number our calculators produce comes from a published, peer-reviewed formula, and this page documents exactly what that formula is, what data it is based on, and where it breaks down. If you want to check our arithmetic, you can.
The core formula
All calculators on RunKcal are built on the MET (Metabolic Equivalent of Task) model, the standard method used in exercise physiology and public health research to estimate energy expenditure from physical activity:
One MET is defined as the rate of energy expenditure at rest — approximately 3.5 ml of oxygen per kilogram of body weight per minute, or about 1 kcal per kilogram per hour. An activity rated at 8 METs therefore consumes roughly eight times the energy of sitting still.
MET values for running come from the Compendium of Physical Activities, a reference database originally compiled by Ainsworth and colleagues and periodically updated. It assigns MET values to hundreds of activities based on measured oxygen consumption in laboratory studies. Running MET values scale with speed:
| Pace | Speed | MET value |
|---|---|---|
| Slow jog | 6.4 km/h (4.0 mph) | 6.0 |
| Easy run | 8.0 km/h (5.0 mph) | 8.3 |
| Moderate | 9.7 km/h (6.0 mph) | 9.8 |
| Steady | 11.3 km/h (7.0 mph) | 11.0 |
| Fast | 12.9 km/h (8.0 mph) | 11.8 |
| Very fast | 14.5 km/h (9.0 mph) | 12.8 |
| Race pace | 16.1 km/h (10.0 mph) | 14.5 |
Why body weight matters more than speed
A result that surprises many runners: over a fixed distance, running faster does not burn substantially more calories. Running a 5K in 22 minutes and running the same 5K in 35 minutes produce total burns within roughly 10 percent of each other.
The reason is visible in the formula. A faster pace raises the MET value, but it also shortens the duration. The two effects largely cancel. What does not cancel is body weight, which appears as a direct multiplier: a 90 kg runner burns approximately 80 percent more calories over the same distance than a 50 kg runner at identical pace.
This is why every RunKcal calculator asks for your weight first. It is the single most important input, and any calculator that omits it cannot give you a meaningful number.
Treadmill incline adjustment
Running on an incline raises energy cost because you are performing vertical work in addition to horizontal movement. Our treadmill calculator applies an incline correction of approximately +0.15 MET per 1 percent of grade, derived from the ACSM metabolic equations for treadmill running.
In practical terms, running at a 5 percent grade increases calorie burn by roughly 20 to 30 percent compared with a flat surface at the same speed. At 10 percent, the increase is substantially larger, though most runners cannot sustain that grade for long enough to realise the full benefit.
Sex adjustment
RunKcal applies a small downward adjustment for female users. This is not arbitrary. At equal body weight, women generally carry a higher proportion of fat mass and a lower proportion of metabolically active lean tissue than men, which produces a modestly lower energy expenditure for the same activity.
The adjustment is deliberately small — a few percent — because the effect is small once body weight is already accounted for. Weight remains by far the dominant variable.
What this calculator cannot do
Being explicit about limitations is more useful than pretending precision that does not exist. The MET model has real constraints:
- It is a population average. MET values were measured across groups of people. Individual metabolic rates vary by roughly ±10–15 percent around the mean, driven by genetics, muscle mass, mitochondrial density, and training history.
- It does not account for running economy. An experienced runner with efficient form uses measurably less oxygen at a given pace than a beginner. Over time, as your economy improves, you will burn slightly fewer calories for the same run — a sign of progress that looks like a setback on paper.
- It ignores environmental conditions. Heat, cold, wind resistance, altitude, and running surface all affect energy cost. Soft sand or deep snow can raise the cost of a run by 30 percent or more.
- It excludes EPOC. Excess post-exercise oxygen consumption — the elevated metabolic rate that persists after hard efforts — is not captured. This adds a small additional burn, typically 5–15 percent of the session total after intense running, and close to zero after easy running.
- It reports gross, not net, calories. Our figures include the resting metabolic rate you would have burned anyway during that time. For a one-hour run, roughly 60–90 kcal of the total is baseline metabolism. This matters if you are precisely tracking a deficit.
How accurate is it, realistically?
For a typical runner on a typical run, expect the estimate to fall within about 10 to 15 percent of your true expenditure. That is comparable to a mid-range GPS watch and considerably better than the readout on most gym cardio machines, which frequently overestimate by 20 percent or more. It is not laboratory-grade, and no formula-based calculator can be.
Why our number differs from your watch
If your Garmin, Apple Watch, or Strava gives a different figure, both numbers are estimates and neither is definitively correct. The difference usually comes down to three things:
First, most fitness watches incorporate heart rate data, which adds personalisation but also introduces its own error — heart rate is affected by caffeine, sleep, heat, stress, and hydration, none of which change your actual energy expenditure. Second, some devices report net calories while others report gross, a difference of 60 to 90 kcal per hour. Third, manufacturers use proprietary algorithms that are not published, so the underlying assumptions cannot be examined.
Our recommendation is to pick one source and use it consistently. The absolute number matters less than tracking the trend over weeks and months.
References
The formulas used on this site are drawn from the following standard references in exercise physiology:
- Ainsworth BE, et al. Compendium of Physical Activities: a second update of codes and MET values. Medicine & Science in Sports & Exercise, 2011.
- American College of Sports Medicine. ACSM's Guidelines for Exercise Testing and Prescription. Metabolic equations for gross VO₂ in walking, running, and treadmill grade.
- Jetté M, Sidney K, Blümchen G. Metabolic equivalents (METS) in exercise testing, exercise prescription, and evaluation of functional capacity. Clinical Cardiology, 1990.
What RunKcal is not
RunKcal is a free educational tool. It is not medical advice, it is not a substitute for consultation with a physician or registered dietitian, and it should not be used to guide clinical decisions. If you are managing a medical condition, planning a significant change in diet or training load, or recovering from injury, speak to a qualified professional who can assess your individual circumstances.
Corrections and contact
If you spot an error in a formula, a MET value, or a calculation, we want to hear about it. Corrections are made promptly and this page is updated when the underlying methodology changes. Write to hello@runkcal.com or use the contact page.
Last reviewed: July 2026