Endurance fuelling
Carbs per hour calculator.
Enter your expected finish time and see the carbohydrate range sports-nutrition research gives for that duration, in grams per hour and in total.
Inputs
Carbohydrate target
Enter your finish time.
How many carbs per hour should I take in a marathon?
The IOC consensus review by Burke and colleagues gives three bands by duration. In sustained high-intensity sport lasting about 1 hour, small amounts of carbohydrate, even a mouth rinse, help performance. For longer events, 30 to 60 g per hour is an appropriate target. In events longer than 2.5 hours, intakes of up to 90 g per hour may help, using products with blends of different carbohydrates so the gut can absorb them. Jeukendrup adds that a single carbohydrate source is oxidized at up to about 60 g per hour, and that higher rates need multiple transportable carbohydrates (for example maltodextrin with fructose).
This tool applies those bands to your finish time: up to 60 minutes shows the small-amounts guidance, over 60 minutes up to 2.5 hours shows 30 to 60 g per hour, and over 2.5 hours shows 30 to 60 g per hour with the up-to-90 stretch range. Total grams are the hourly rate multiplied by hours, for example 4 hours at 30 to 60 g per hour is 120 to 240 g. The ISSN ultra-marathon position stand gives 30 to 50 g per hour as a carbohydrate aim for ultra racing, within the same range.
Use the range as a starting point and build up in training. Gut tolerance is individual and the research ranges are not a target to hit on race day without practice.
Frequently asked questions
How many carbs per hour for a marathon?
Research gives 30 to 60 g per hour for events of roughly 1 to 2.5 hours, and up to 90 g per hour for events longer than 2.5 hours using blended carbohydrate sources. Most recreational marathon finish times are in the longer band, so the higher end is worth discussing with a dietitian and practising in training.
Is 90 g of carbs per hour safe?
Burke and colleagues say events longer than 2.5 hours may benefit from up to 90 g per hour, with blended carbohydrates to help absorption. Many people get stomach upset at high rates, so it is built up gradually in training. It is a research range, not a requirement.
Do I need carbs for a 10K or a one-hour run?
For efforts of about an hour the research describes only small amounts of carbohydrate, including a mouth rinse. Under about an hour this tool shows 0 g per hour as the published target.
Do these grams include the carbs in my sports drink?
Yes. The target is total carbohydrate from everything you take in: gels, chews, drink and food. The gels calculator subtracts the carbohydrate you drink.
Sources
Checked
- Burke, Hawley, Wong and Jeukendrup, Carbohydrates for training and competition (IOC consensus), J Sports Sci 2011
- Jeukendrup, A step towards personalized sports nutrition: carbohydrate intake during exercise, Sports Med 2014
- Tiller et al., ISSN position stand: nutritional considerations for single-stage ultra-marathon training and racing, J Int Soc Sports Nutr 2019
Ranges are quoted from the sources above and are general research or position-statement figures. Gel, powder and drink contents, spare gels and stop intervals are your own inputs; defaults are placeholders. One kilogram of body mass is treated as one litre of fluid.
Scope
Education only, not medical or dietetic advice. Needs differ by person, event, heat and training, and the published ranges are general. Try any fuelling or hydration plan in training, not for the first time on race day. If you have a medical condition (including diabetes, kidney or heart disease or high blood pressure), are pregnant or breastfeeding, or are under 18, ask your doctor or a registered dietitian first. Stop and get medical help for confusion, vomiting, severe headache, fainting or swelling of the hands and feet during or after a long effort.