Exercise Fat Burn Estimator
Estimate how many grams of fat your body oxidises during a workout — in grams, not just calories. Pick your activity or paste data straight from your fitness watch.
Fat oxidised during exercise
grams of fat, net of what you would have burned resting
Fat burned during exercise is not the same as fat lost — total intake over the day decides that.
How this is worked out: total energy is MET × body weight (kg) × hours, minus 1 MET × body weight × hours for the energy you would have burned resting anyway. The fat share of that net energy falls on a straight line from 65% at MET 3.5 (an easy walk) to 35% at MET 10 (a hard run), with amino acid oxidation running 2–5% and the remainder from glycogen. Those endpoints are conventional respiratory-exchange-ratio figures; the line between them is an interpolation, not a measured curve. Your own split depends on fitness, training history, and how fat-adapted you are.
Net Calories
— kcal
Protein oxidised
— g
Glycogen Burned
— g
Why grams of fat instead of calories?
Fat-adapted athletes and carnivore dieters burn a higher proportion of fat during exercise. The fat oxidation ratio varies continuously with intensity, based on the respiratory exchange ratio (RER) from exercise physiology research:
- MET 3.5 and below: 65% of energy from fat — easy walking, yoga
- Between MET 3.5 and 10: a straight line between 65% and 35% — brisk walking, cycling, weightlifting, swimming
- MET 10 and above: 35% from fat — running, HIIT, jump rope
MET (Metabolic Equivalent of Task) values from the Compendium of Physical Activities (2024). 1g of fat = 9 kcal. 1g of protein = 4 kcal. 1g of glycogen = 4 kcal. Energy is counted net of 1 MET of resting metabolism.
Fat-adapted carnivore dieters may burn an even higher percentage of fat at moderate intensity compared to carbohydrate-fueled athletes.
These are estimates. Actual fat oxidation depends on your metabolic state, training history, and whether you are fat-adapted.
Estimates based on MET values from the Compendium of Physical Activities (2024). Fat oxidation ratios derived from exercise physiology research on respiratory exchange ratios. Educational and informational purposes only — not medical or nutritional advice. Consult your healthcare provider before making dietary changes.