Race Fueling Calculator
Plan your carbohydrate, fluid and sodium intake for a long race based on your expected duration.
How to use the race fueling calculator
- Enter your expected race duration.
- Choose a carb intake rate (60 g/hr is standard, up to 90 g for a trained gut).
- Click Calculate plan to see total carbs, gels, fluid and sodium.
Train your gut
High carb intake during exercise is a trainable skill. Practising race fueling in long runs improves tolerance and lets you absorb more without stomach distress on race day.
Why carbohydrate intake limits long races
Your body stores only enough glycogen for roughly 90-120 minutes of hard running. Beyond that, taking in carbohydrate during the race keeps your blood sugar and pace from collapsing. Most endurance athletes target 60-90 grams of carbohydrate per hour for efforts over about 90 minutes, with the upper end requiring a trained gut.
Train your gut, not just your legs
Absorbing 60-90 grams of carbohydrate per hour is a skill that improves with practice. Rehearsing your race fuelling during long runs raises your tolerance and reveals which products sit well, so race day holds no nasty surprises. This calculator turns your expected duration and intake rate into a concrete plan: total carbs, number of gels, fluid, and sodium.
Carbohydrate, fluid and sodium targets by race duration
| Race time | Total carbs | 22 g gels | Fluid | Sodium |
|---|---|---|---|---|
| 1:00 | 60 g | ~3 | 0.4–0.8 L | 300–600 mg |
| 1:30 | 90 g | ~4 | 0.6–1.2 L | 450–900 mg |
| 2:00 | 120 g | 5–6 | 0.8–1.6 L | 600–1,200 mg |
| 3:00 | 180 g | ~8 | 1.2–2.4 L | 900–1,800 mg |
| 4:00 | 240 g | ~11 | 1.6–3.2 L | 1,200–2,400 mg |
| 5:00 | 300 g | ~14 | 2.0–4.0 L | 1,500–3,000 mg |
Carbohydrate is set at 60 g/hour, the reliable middle of the 30–90 g range; sub-90-minute efforts can sit lower. Fluid and sodium are per-hour ranges — lean high in heat and if you are a heavy, salty sweater. Measure your own sweat rate to personalise the fluid column.
Frequently asked questions
How many carbs do I need during a marathon?
Most endurance athletes target 60–90 grams of carbohydrate per hour for efforts over about 90 minutes. Longer and faster races sit at the upper end.
How many gels should I take in a race?
It depends on duration and gel size. At 60 g/hr with 22 g gels, a four-hour race needs roughly 11 gels — plan and practise this in training.
How many carbs do I need during a marathon?
Most runners target 60-90 grams per hour for efforts over 90 minutes, with faster and longer races at the upper end. Practise the rate in training first.
How many gels should I carry?
Divide your hourly carb target by the carbs per gel, then multiply by race hours. At 60 g/hour with 22 g gels, a four-hour race needs roughly eleven gels.
Why do I get stomach problems with race fuelling?
Usually the gut is undertrained for high carb intake, or the concentration is too strong without enough fluid. Practising fuelling in training and pairing gels with water both help.
How much sodium do I need in a long race?
Plan on roughly 300–600 mg per hour, toward the higher end when it is hot or you finish runs with salt streaks on your skin. The table below scales it by race length: a four-hour marathon works out to somewhere between about 1,200 and 2,400 mg in total.
Related tools
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Enter a goal marathon finish time to get the pace you need to hold, your halfway target, and cumulative splits.
Sweat Rate Calculator
Work out how much you sweat per hour so you can plan hydration for training and racing.
Calories Burned Running
Estimate how many calories you burn on a run based on your weight, pace, and duration.