Calculate how much to drink before, during, and after your run based on distance, temperature, and your bodyweight.
Total fluid loss
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ml estimated
During run (per km)
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ml per km
Post-run recovery
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ml to replace
Hydration timeline
⚠️ Hot weather warning: In temperatures above 25°C, consider electrolyte replacement (sodium, potassium) not just water. Plain water alone can dilute sodium levels (hyponatremia) on runs over 60 minutes. Use a sports drink or electrolyte tablet for anything over an hour in the heat.
⚠️ These are estimates only. Sweat rate varies enormously between individuals — studies show a range of 0.5L to over 2.5L per hour among runners of similar size. Factors including fitness level, heat acclimatisation, genetics, and individual physiology all play a role. Use these figures as a starting point and adjust based on how you feel and the colour of your urine post-run.
Signs of dehydration: Dark urine, headache, dry mouth, fatigue, reduced performance. Aim for pale yellow urine as your hydration benchmark.
Don't over-drink: Drinking too much water (hyponatremia) is as dangerous as dehydration. Drink to thirst — not on a rigid schedule unless racing in heat.
How to measure your own sweat rate more accurately:
1. Sweat rate test — weigh yourself (without clothes) immediately before and after a one-hour run at a known pace and temperature. Every 1kg of weight lost ≈ 1 litre of sweat. Add back any fluid you drank during the run to get your true sweat rate. Repeat in different conditions to build a personal picture.
2. Sweat patch testing — adhesive patches worn during exercise that collect sweat for analysis. Available through sports science labs and some performance centres. Measures both sweat volume and sodium concentration — useful for heavy or salty sweaters.
3. Urine colour chart — the simplest practical tool. Aim for a pale straw yellow (colour 1–3 on the standard chart) both before and after running. Dark yellow or amber means you started or finished dehydrated. Available as a free printable from most sports nutrition providers.
4. Body weight tracking — weigh yourself at the same time each morning. A drop of more than 1% of body weight from your baseline over consecutive training days suggests accumulated dehydration that needs addressing.
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