How this calculator works

The stroke settings use metabolic equivalent (MET) values from the 2024 Adult Compendium of Physical Activities, the reference dataset for the energy cost of exercise. Gentle swimming that isn't lap work rates 6.0 METs, easy front crawl 5.8, moderate front crawl 8.0, fast front crawl 10.5, recreational breaststroke 5.3 rising to 10.3 when swum hard, easy backstroke 4.8, butterfly 13.8, and open water at race effort around 10.5. Your calories are then METs multiplied by your weight in kilograms multiplied by hours swum. The result is gross calories, meaning it includes what you would have burned resting over the same period.

Calories burned by stroke

For a 70 kg swimmer over a full hour, gentle swimming burns around 420 kcal, easy front crawl around 405, moderate front crawl around 560, and fast front crawl around 735. Breaststroke spans a huge range, roughly 370 kcal per hour swum recreationally but around 720 swum hard, because its high-drag position punishes effort. Easy backstroke sits near 335, and butterfly tops everything at around 965 kcal per hour, though almost nobody sustains butterfly for anything like an hour. Calories scale directly with body weight, so an 85 kg swimmer adds roughly a fifth to every figure and a 60 kg swimmer takes roughly a seventh off.

Calories burned by distance

Front crawl costs a 70 kg swimmer roughly 200 kcal per kilometre, so a one-mile swim comes to around 320 kcal and a 5 km open water swim lands between about 850 and 1,000 kcal depending on effort. Distance answers hide a quirk worth knowing: steady crawl actually costs slightly more per kilometre than fast crawl, because you spend longer in the water even though each minute is cheaper.

Open water and cold water

Open water usually costs more than the pool. Chop, currents, sighting and wetsuit drag push the true figure above calm-pool numbers, often by 10 to 25%. Cold water adds a different effect: your body works to defend its core temperature, and every open water swimmer knows the ferocious hunger that follows a cold swim. That post-swim appetite is real, and it is exactly when a warm drink and something properly calorie-dense earn their place.

Why your number is an estimate

Swimming is the sport where technique moves the numbers most. An efficient swimmer travels further per calorie than a thrashing one, and MET values are population averages that can't see your stroke. Rest matters too: a 60-minute pool session with 15 minutes at the wall is really about 45 minutes of continuous swimming, so enter your active time, not your session time. Treat the result as a planning figure and refine it with experience.

Refuelling after your swim

Swimming is the one endurance sport where you cannot eat during the effort, so the whole refuel lands afterwards, usually when you're cold, ravenous and nowhere near a kitchen. That combination is why swimmers so often either raid the vending machine or eat nothing at all. A compact, calorie-dense option in your swim bag solves it: our high calorie energy bars pack 557 kcal into a single 120g bar at 4.64 kcal per gram, and each bar also mixes into a warm porridge, which lands especially well after cold water. For longer sessions and race days, see our open water swimming nutrition guide, and if you're comparing options, the highest calorie bars in the UK ranked by energy per gram.

Frequently asked questions

How many calories do you burn in 30 minutes of swimming? For a 70 kg swimmer, roughly 210 kcal swimming gently, 280 kcal at a moderate front crawl, and 370 kcal swimming hard.

How many calories is a 20 minute swim? Around 140 kcal gently and 190 kcal at moderate effort for a 70 kg swimmer. Short swims still add up across a week.

How long should I swim to burn 1,000 calories? At a moderate front crawl, a 70 kg swimmer needs roughly an hour and three quarters of continuous swimming, or about an hour and 20 minutes at a fast pace. Few people swim that long without rest, so most 1,000 kcal days are split across sessions.

Does swimming burn more calories than running? Minute for minute, hard swimming and steady running are close, at roughly 8 to 10 METs each. Swimming spares your joints and works the whole body, while running usually edges it for raw burn per hour at equivalent effort.

Working out your numbers for other sports? Try our cycling calorie calculator, ultra running calorie calculator and rucking calorie calculator.

Written by James, founder of Flaming Phoenix and the maker of Phoenix Bars. Calculator methodology based on the 2024 Adult Compendium of Physical Activities. Updated August 2026.