Calculator
Fueling Calculator
Work out how many carbs, how much fluid and sodium you need while running. Enter the expected duration, your body weight, the expected temperature and how much you tend to sweat, the calculator does the rest.
Your data
If you are not sure: check how soaked your shirt gets, or whether it leaves salt stains once dry, the latter is a sign of heavy sweating.
Hourly needs
Carbohydrate
g/hour
g total for the distance
You typically do not need carbohydrate fueling for this duration, water is enough.
Fluid
ml/hour
liters total for the distance
Sodium
mg/hour
mg total for the distance
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I am interestedHow do we calculate fueling needs?
Carbohydrate needs depend mainly on duration, not distance: runs under 1 hour typically do not need it, 1-2.5 hours calls for 30-60 grams per hour, and beyond 2.5-3 hours up to 90 grams per hour can be warranted, based on ACSM/ISSN and International Olympic Committee sports nutrition recommendations.
Fluid and sodium needs, on the other hand, are highly individual: body weight, temperature and your own sweat tendency all matter. The estimate starts from the ACSM 0.4-0.8 liter/hour fluid and 500-700 mg/liter sodium guidelines and factors these in. The exact number can only be measured with an individual sweat test, but this is a solid starting point.
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Frequently asked questions
Why does duration matter, not distance?
Your risk of depleting glycogen stores depends mainly on how long you are out there, not the distance you cover. The longer you run, the more your stores are drawn down, so both the hourly rate and the total amount you should replace go up. If you cover the same distance faster, you are exposed to that risk for less time, so both your hourly rate and total can end up lower than for a slower, longer run.
What does the sweat level question mean?
How much you sweat varies a lot between individuals, and it is the biggest factor in your fluid and sodium needs. Without precise measurements (weighing yourself before and after a run), your own experience (how soaked your clothes get, whether they leave salt stains once dry) is a good approximation.
Should I enter goal time or pace?
Whichever you know more precisely. If you have a specific goal time for a race, enter that. If you know your planned pace instead (e.g. for a training run), enter the pace, the calculator works out the duration from that.
How accurate is this estimate?
It is a general estimate based on recognized sports science guidelines, but individual variation can be significant (gut tolerance, fitness, heat acclimatization). For long distances, it is worth testing and fine-tuning your own fueling plan during training.
The result is a general estimate, not medical or nutritional advice. Individual tolerance, health conditions and circumstances can significantly affect actual needs. People sensitive to sodium (e.g. with high blood pressure) should consult a professional.
The calculation is based on ACSM/ISSN sports nutrition position stands and the International Olympic Committee 2010 consensus statement (carbohydrate: 30-90 g/hour depending on duration; fluid: 0.4-0.8 l/hour; sodium: 500-700 mg per liter of fluid).