Carbs per hour calculator
How many grams of carbohydrate to take each hour of an ultra.
How does the carbs per hour calculator work?
It starts from your body weight and how hard you will run: about 0.5 g of carbohydrate per kilogram per hour at an easy effort, rising to 1.2 g at a very hard one. Then it applies what the gut can usually absorb. One carbohydrate source tops out near 60 g an hour, and a glucose and fructose mix near 90 g an hour. If you pick a sensitive gut, the number is held lower still.
It is the same maths the UltraCalcPal app uses, so the number here matches the one in your plan.
How to use the number
- Treat it as a target to build towards in training, not a number to hit on race day for the first time.
- Spread it across the hour in small amounts: a gel, some chews or a bottle every 20 to 30 minutes is easier on the stomach than one large dose.
- If a result says it was capped, that is the gut limit you chose. Raise it slowly with practice, see gut training for ultras.
Frequently asked questions
How many carbs per hour for an ultramarathon?
Most runners land between 40 and 90 g an hour, depending on body weight, effort and how well the gut is trained. Slower, longer races sit at the lower end. Fast races with a trained gut and a glucose and fructose mix sit at the top.
Why is the glucose to fructose split 60 to 40?
Glucose and fructose use different routes into the blood, so together they can be absorbed faster than either alone. A 60 to 40 mix is a common starting point, and many products are made to that ratio.
Does it work for a 50K or a marathon?
Yes. Enter the time you expect to take. For runs under about two hours you rarely need more than a few sips of a sports drink, so the total will look small.