Fitness trackers and gym machines show calories burned, but where do the numbers come from? Most estimates rely on a simple idea called the metabolic equivalent of task (MET). Understanding it lets you check any estimate yourself and put the number in context.

What Is a MET?

One MET is the energy you use sitting at rest, roughly one calorie per kilogram of body weight per hour. Every activity is given a MET value that says how many times more energy it uses than resting. An activity rated 4 METs uses about four times as much energy as sitting still.

The Formula

Calories burned = MET × body weight (kg) × time (hours).

The MET values come from the Compendium of Physical Activities, a research database. These are approximate values for an average person:

  • Brisk walking at about 5.6 km/h (3.5 mph): around 4.3 METs.
  • Running at about 9.7 km/h (6 mph): around 9.8 METs.
  • Cycling at a moderate pace of roughly 19 to 22 km/h (12 to 14 mph): around 8 METs.
  • Swimming at a moderate pace: about 6 METs.
  • Gentle yoga or stretching: roughly 2.5 to 3 METs.

Worked Examples for a 70 kg Person

  • Running for 30 minutes: 9.8 × 70 × 0.5 = 343 calories.
  • Brisk walking for 60 minutes: 4.3 × 70 × 1 = 301 calories.
  • Cycling for 45 minutes: 8 × 70 × 0.75 = 420 calories.

A person who weighs more burns more for the same activity, and a lighter person burns less, which is why the formula includes body weight.

Total Calories vs Net Calories

The result above includes the calories you would have burned anyway if you had stayed at rest. To estimate the extra, or net, calories from exercise, subtract 1 MET. For the run: (9.8 − 1) × 70 × 0.5 = 308 calories above what resting would have used. This matters if you eat back exercise calories, because counting the full number overstates the benefit.

How Accurate Are These Numbers?

They are estimates. Real calorie burn varies by fitness level, age, sex, body composition, terrain, temperature and technique. Studies of wearables and machines have found errors that can be 20% or more, and heart-rate-based estimates are often somewhat better than step-based ones. Use the figure to compare activities and track trends, not as an exact measurement. Our guide to calorie needs and weight loss shows how to use daily estimates safely.

Exercise Is Not the Whole Picture

Most of the calories you burn in a day come from your resting metabolism and everyday movement, not from workouts. A 30-minute run burning 340 calories is real, but it is easy to undo with a snack. Exercise has major benefits for heart health, mood, sleep, bone density and metabolic health that have nothing to do with calories, so it is worth doing even if the scale does not move quickly.

Choosing Activities

  • Pick something you enjoy, because the best programme is the one you stick to.
  • Mix steady cardio with strength training to keep muscle, which supports your resting metabolism.
  • Build up gradually if you are new to exercise, and increase time or intensity by small steps.
  • Walking more through the day adds up. A 60-minute brisk walk burns about as much as 30 minutes of running for many people, with lower impact on joints.

When to Get Advice

If you have a heart condition, high blood pressure, diabetes, joint problems or are pregnant, speak to a doctor before starting an intense routine. If you have a history of disordered eating, avoid focusing on calorie numbers and seek professional support.

Your Next Step

Choose your usual activity, find its MET value, and multiply by your weight and time. Then use our Calories Burned calculator to compare activities side by side. This article is general information, not medical advice.