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About this tool
Calories burned swimming by stroke, effort and time, with pool distance, pace per 100 m and calories per length.
This calculator estimates the energy cost of a swim from the MET value of your stroke and effort, using the ACSM formula kcal/min = MET × 3.5 × body-mass-in-kg ÷ 200. Pick a stroke — the MET values come from the 2011 Compendium of Physical Activities, water-activity category 18, ranging from 3.5 for moderate treading to 13.8 for butterfly — enter your weight and minutes in the water, and optionally your lengths and pool length to get distance, pace per 100 m and calories per length. It reports both gross calories and net calories with the resting 1 MET removed, which is the figure to use when comparing a swim against food.
Open Swimming Calorie Burn Calculator on AltFTool — it loads instantly in your browser.
Enter the values you already know.
Fine-tune the options to match your scenario.
Read the result and use it in your planning or reporting.
It subtracts the 1 MET you would have burned resting anyway, so the number you compare against food is not inflated by roughly 60–100 kcal an hour.
Each option carries its published Compendium MET value and activity code, so recreational backstroke at 4.8 MET is never confused with training backstroke at 9.5.
Enter lengths and pool length and it derives total distance, minutes per 100 m and calories per 100 m alongside the session total.
For a 70 kg swimmer doing steady freestyle at 5.8 MET, roughly 425 kcal an hour gross — the formula is 5.8 × 3.5 × 70 ÷ 200, or about 7.1 kcal per minute. Hard freestyle at 9.8 MET roughly doubles that, and the figure scales directly with body mass, so a 90 kg swimmer burns about 29% more than a 70 kg one at the same stroke.
One MET is resting metabolic rate, defined as 3.5 mL of oxygen per kilogram of body mass per minute. Because it is expressed per kilogram, a heavier body consumes proportionally more oxygen at the same MET, and one litre of oxygen is taken as 5 kcal — which is where the ÷ 200 in the formula comes from.
Use net when you are comparing the swim against calories eaten, and gross when you are logging total energy expenditure for the day. Net removes the 1 MET of resting metabolism you would have spent lying on the sofa for the same period, which is around 70 kcal an hour for a 70 kg person.
Treat it as an estimate with a wide margin. Compendium MET values are population averages that ignore swimming technique, water temperature, rest between sets and individual efficiency — a skilled swimmer covers the same distance for far less energy than a beginner. It is informational only; talk to a doctor or a dietitian before building a weight-loss plan around any calorie figure.
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