Fuelling & Hydration Calculator
How many carbs, how much fluid, how much sodium — worked out from your run length, effort and conditions, not a one-size-fits-all number.
Enter your expected duration, effort and conditions, and I'll give you a practical per-hour target for carbs, fluid and sodium — the same starting point I use when planning race-day fuelling with the runners I coach in Manchester and online.
Plan your fuel & fluids
Fill in your run, and I'll give you an hourly target plus a total for the whole effort.
Enter your expected duration and hit "Calculate" — your carb, fluid and sodium targets will appear here.
Total for the whole run
Race-day timing
Caffeine gels
These are sensible starting ranges, not a prescription — sweat rate and gut tolerance vary a lot between runners. Test any fuelling plan in training well before race day, never for the first time on race day itself, and speak to a doctor or dietitian if you have any medical condition (including diabetes or a history of GI issues) before making changes to your fuelling.
Why fuelling needs vary so much
Carbohydrate needs scale mainly with duration: under 45 minutes, water is normally enough. Between 45 and 60 minutes is a genuine grey area — a mouth rinse or a small amount can give a slight edge for a hard effort, but it's optional, not essential. Past 60 minutes is where real intake starts to matter, typically 30-60g of carbs per hour. Beyond 2.5 hours, well-practised guts can often handle 60-90g per hour or more using multiple carb sources (glucose and fructose together) — which is why "practice race-day fuelling in training" matters so much. Figures above that, up to around 120g/hour, only apply to athletes who've specifically and repeatedly trained their gut to tolerate that much — it's not a target most runners should aim for without extensive practice first.
Fluid needs depend far more on conditions, sweat rate and body size than on pace — a 400ml/hour sweat rate in cool weather can easily become 900ml/hour or more in heat and humidity. There's no universal number here, only a sensible range to test and refine.
Sodium matters most in hot conditions and for "salty sweaters" (if you finish runs with visible white salt marks on your kit, you likely lose more sodium than average and may need the higher end of the range, or beyond it).
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Want a plan that puts this into practice for your actual race, not just the numbers? Take a look at bespoke training plans or online coaching, check your race-day splits, or get in touch for a free, no-pressure chat.