Race Nutrition Calculator — Carbs, Fluid and Sodium per Hour
Work out what to carry, in grams and in actual pouches. Tell it how long you expect to be out there and this returns your carbohydrate, fluid and sodium targets per hour and for the whole race — then turns those numbers into a specific list of Spring products, with quantities, and loads the lot into your basket in one click.
Most fuelling advice stops at “60 to 90 grams of carbohydrate an hour” and leaves you to do the arithmetic at 11pm the night before a race. The arithmetic is where it goes wrong. Gels are not all the same size, calories are not the same thing as carbohydrate, and the number that matters — grams per hour — is not printed on the front of most packets. This does the conversion for you.
The calculator
Don't know it? Measure it here — it makes the fluid and sodium figures yours rather than an average.
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g carbohydrate per hour
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ml fluid per hour
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mg sodium per hour
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g carbohydrate in total
What to carry
How to take it
Where the carbohydrate number comes from
Carbohydrate targets are set by how long you will be working, not by how far you are going or how much you weigh. The limiting factor is how fast your intestine can absorb sugar, and that is roughly the same whether you are 55 kg or 90 kg.
| Duration | Carbohydrate per hour | Why |
|---|---|---|
| Under 1 hour | 0–30 g | Muscle glycogen covers it. Fuelling is optional and mostly about comfort. |
| 1 to 2 hours | 30–60 g | Enough to protect the back end of the effort without loading the stomach. |
| 2 to 3 hours | 60 g | Around the ceiling for glucose alone. Beyond this you need a glucose and fructose mix. |
| 3 to 5 hours | 60–90 g | The range where a trained gut and multiple transportable carbohydrates pay off most. |
| Over 5 hours | 60–80 g | Intensity drops, palate fatigue sets in, and consistency beats maximum. |
Your gut is the variable, not your legs. Carbohydrate absorption is trainable, which is why this calculator asks about your fuelling experience. If you have never deliberately practised taking 70 g an hour, race day is the wrong place to find out whether you can. Build up across several long sessions, using the products you actually intend to race with.
Where the fluid and sodium numbers come from
Sweat rate varies enormously — published ranges run from under 0.5 to over 2.5 litres an hour — and sweat sodium varies more than tenfold, roughly 200 to 2,300 mg per litre with an average near 950. If you have not measured yours, this calculator estimates it from your body weight and the conditions, then plans to replace about 75% of it. That is deliberate: replacing everything you lose is neither achievable at high sweat rates nor desirable, and sustained intakes above about a litre an hour raise the risk of hyponatremia.
If you have run a sweat rate test, enter the number and the fluid and sodium figures stop being an average and start being yours.
Why the plan is built in grams, not gels
“How many gels do I need” is an unanswerable question until you know how many grams each one carries, and the spread across our own range is wide: 12 g in a Speednut, 17 g in a Canaberry, 28 g in an Awesome Sauce, 50 g in a Peach Cobbler XL. Two products with similar calories can be twice as far apart on carbohydrate. Every number in the plan above comes from the same verified panel data published on our complete nutrition page, so you can check the arithmetic yourself.
Two products are deliberately not carbohydrate tools. Speednut and the Blueberry Endurance Meal carry 12 g and 22 g of carbohydrate against 19 g and 24 g of fat. They exist for the long, slow, late part of a day — night sections, hiking grades, the hour when nothing sweet will go down. The calculator only puts them in a plan when the event is long enough to warrant them, and never counts on them to hit an hourly carbohydrate target.
Common questions
How many carbs per hour should I take during a race?
It depends on how long you will be out there and how well trained your gut is. Under an hour you need very little. Between one and two hours, 30 to 60 g of carbohydrate per hour is enough. Past two hours, 60 g per hour is the working figure for most people, and past three hours a well-trained gut can absorb 70 to 90 g per hour using a mix of glucose and fructose. If you have never deliberately practised fuelling, start at 40 to 50 g per hour and build up in training rather than trying a new number on race day.
How much should I drink during a race?
Aim to replace roughly 75% of what you sweat, not all of it. For most runners in mild conditions that is 400 to 600 ml per hour, rising towards 800 ml in heat. Sustained intakes above about a litre an hour raise the risk of hyponatremia, which is dilution of blood sodium and more dangerous than the mild dehydration most runners worry about. The only way to know your own figure is to measure it with a sweat rate test.
How much sodium do I need per hour?
Sodium loss is sweat volume multiplied by sweat sodium concentration, and concentration varies more than tenfold between people — roughly 200 to 2,300 mg per litre, averaging near 950 mg/L. At a typical sweat rate that works out to somewhere between 300 and 1,000 mg per hour for most athletes. Higher sweat rates and hotter conditions push it up. If you cramp, crust up with salt, or have had a bad day in the heat, assume you are at the high end.
How many gels do I need for a marathon?
Work backwards from grams, not from gels, because gels are not all the same size. At 60 g of carbohydrate per hour, a four-hour marathon needs about 240 g of carbohydrate in total. In Spring products that is roughly nine Awesome Sauce, or five Peach Cobbler XL, or a mix of the two. A 100-calorie gel from a typical brand carries 22 to 25 g, so the same race would need ten or eleven of those.
When should I start fuelling in a race?
Within the first 20 to 30 minutes, before you feel like you need it. Carbohydrate takes time to reach the muscle, and once you are behind, catching up while working hard is very difficult. Then keep taking it at regular intervals — every 20 to 25 minutes is easier on the stomach than a large dose every hour.
Can I train my gut to handle more carbohydrate?
Yes. Carbohydrate absorption is trainable, and repeatedly practising race-day fuelling in long training sessions raises how much you can take without distress. That is why this calculator asks about your fuelling experience rather than giving everyone the same number. Build up over weeks, not days, and practise with the exact products you plan to race with.
What should I eat during an ultra when nothing sweet will go down?
This is the point where a fat-based, savoury or nut-based option earns its place. Speednut and the Blueberry Endurance Meal are built for it — they carry 250 and 310 calories on 12 g and 22 g of carbohydrate, so they are calorie-dense rather than carbohydrate-dense. They are not the tool for hitting a grams-per-hour target, but at hour nine when your palate has quit, calories you can actually swallow beat calories you cannot.
Does this calculator account for my body weight?
For fluid and sodium, yes — sweat losses scale with body size, so the fluid estimate is adjusted for weight and conditions. For carbohydrate, no, and deliberately so. Current guidance sets carbohydrate targets in absolute grams per hour rather than per kilogram, because the limit is intestinal absorption rather than body mass.
Carbohydrate, sodium and calorie figures for every product come from our published nutrition panels — see the complete nutrition data page. Nutrition panels for the drink mixes are still being verified and are not yet used in these calculations. Last reviewed: 14 August 2026.