How are calories burned calculated?

This calculator uses the MET (Metabolic Equivalent of Task) formula: kcal = MET x body weight in kg x duration in hours. MET values represent the energy cost of an activity relative to sitting at rest (MET 1). Walking at a moderate pace has a MET of 3.5, meaning it burns 3.5 times as many calories as sitting still. Multiply by kilograms and hours to get kilocalories, then by 4.184 to convert to kilojoules.

Why does body weight affect calories burned?

A heavier body requires more energy to move. The MET formula accounts for this directly: a 100 kg person burns roughly twice as many kilojoules doing the same activity for the same duration as a 50 kg person. This is why two people doing the same class or run burn different amounts, and why weight loss itself tends to slow the rate of energy burn over time.

Is it better to track kJ or kcal in New Zealand?

In New Zealand, food labels display kilojoules (kJ) by law, so kJ is the most practical unit for comparing energy burned against food consumed. This calculator shows kJ as the primary result. If you use a fitness tracker or app that shows kcal (sometimes called Calories with a capital C), divide the kJ figure by 4.184 to convert.

Calories Burned Calculator

This calculator works out how many kilojoules (kJ) and kilocalories (kcal) you burn during exercise, sport or everyday activity, using the MET (Metabolic Equivalent of Task) method used in exercise science. Choose from more than 30 activities grouped by type, including walking, running, cycling, swimming, gym classes, yoga, team sports and everyday tasks like gardening and housework, then enter your body weight in kilograms and how long you did the activity for in minutes. The calculator instantly returns the total kilojoules burned, shown as the headline figure because that is the unit used on New Zealand food labels, along with the equivalent in kilocalories and a per-minute breakdown in both kJ and kcal so you can compare the intensity of different activities. It also translates the result into everyday food items, such as apples, bananas or a flat white, so you can see roughly how much energy you have burned in terms you recognise. Behind the scenes it multiplies the activity's MET value by your weight and the duration in hours, then converts to kilojoules. Because the figures are based on average fitness and body composition, treat them as a useful guide rather than an exact measurement. Actual energy burn varies with fitness level, terrain, effort within an activity and individual metabolism, so a heart-rate based fitness tracker will give a more personal estimate for any single session.

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Activity

Body weight (kg)

Duration (minutes)

min

549 kJ

kilojoules burned

131 kcal

Per minute18.3 kJ/min

Per minute4.4 kcal/min

Equivalent food energy

How it works

The calculator uses the MET (Metabolic Equivalent of Task) method, which is the standard approach used in exercise science and published research. Each activity is assigned a MET value that represents how much harder it makes the body work compared to sitting at rest (MET 1.0).

The formula

Energy (kcal) = MET x body weight (kg) x duration (hours)

To convert to kilojoules, multiply kcal by 4.184. So a 75 kg person walking at a moderate pace (MET 3.5) for 30 minutes burns: 3.5 x 75 x 0.5 = 131 kcal = 549 kJ.

What is a MET value?

MET stands for Metabolic Equivalent of Task. A MET of 1 is the energy used sitting quietly. A MET of 7 means the activity uses seven times as much energy. Walking slowly is around MET 2.8, running hard is MET 11 to 14, and vigorous cycling is MET 10 to 12. MET values used here are based on the Compendium of Physical Activities.

Limitations

MET-based estimates assume average fitness and body composition. Actual burn varies with fitness level, terrain, temperature, exercise intensity within an activity type, and individual metabolism. Treat results as a useful guide rather than a precise measurement. A fitness tracker with heart rate data will give a more personal estimate during a specific session.

Worked example

A 75 kg person goes for a moderate-paced walk (5 km/h) for 30 minutes.

MET for walking moderate: 3.5
Duration in hours: 30 / 60 = 0.5 h
kcal burned: 3.5 x 75 x 0.5 = 131 kcal
kJ burned: 131 x 4.184 = 549 kJ
That is equivalent to approximately 1.8 apples at 310 kJ each

kJ vs kcal in New Zealand

New Zealand food labels show energy in kilojoules (kJ) by law, following the Australia New Zealand Food Standards Code. Most fitness apps and international sources use kilocalories (kcal), sometimes written as Calories (with a capital C). One kcal equals 4.184 kJ. When comparing what you burn against what you eat, use kJ throughout so the numbers match your food packaging directly.

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