Endurance fuelling
Gels needed calculator.
How many energy gels to carry for a half marathon, marathon or long ride, from your finish time, your carbs-per-hour plan and the carbs in your gel.
Inputs
Gels to carry
Enter your finish time.
How many gels do I need for a half marathon or marathon?
The arithmetic is total carbohydrate divided by grams per gel. Total carbohydrate is your hourly target multiplied by hours, minus anything you take from a sports drink. The result is rounded up to a whole gel. The hourly target should come from the research range: 30 to 60 g per hour for events from about 1 to 2.5 hours, and up to 90 g per hour beyond 2.5 hours (Burke and colleagues, IOC consensus).
As a worked example only: a 2-hour half marathon at 45 g per hour is 90 g, and with 25 g gels that is 3.6, so 4 gels. A 4-hour marathon at 45 g per hour is 180 g, which is 7.2 gels, so 8. Your gel size, finish time and target will differ. The spacing shown is the finish time divided by the number of gels, which is an even spread and not a published rule.
Frequently asked questions
How many gels for a half marathon?
Hourly carbs times hours, divided by carbs per gel, rounded up. At 45 g per hour for 2 hours with 25 g gels it is 4 gels. Change the finish time, rate and gel size above for your own plan.
How many gels for a marathon?
At 45 g per hour for 4 hours with 25 g gels it is 8 gels. Over 2.5 hours the research allows up to 90 g per hour with blended carbohydrate sources, which would raise that figure.
How often should I take a gel?
The tool spreads gels evenly across your finish time. There is no published interval; start with what you tolerate in training.
Do I need to drink water with a gel?
Follow the instructions on your gel. Some are designed to be taken with water. Your fluid plan is separate; see the fluid intake calculator.
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
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.