Half marathon gels: how many and when
Calculate half marathon gels using carbohydrate per hour, race duration and product labels. Worked two-hour examples and timing you can rehearse.
In this article
To plan gels for a half marathon, combine expected duration, carbohydrate per hour and the amount in each product. Counting packets without reading their labels can leave you far from your intended intake.
For endurance exercise lasting approximately 1–2.5 hours, the sports nutrition consensus uses 30–60 g of carbohydrate per hour as a reference. Duration, intensity and tolerance guide the choice. Every runner does not need the upper end. Thomas and colleagues.
The calculation you need
Total carbohydrate = target in g/hour × duration in hours.
Subtract carbohydrate from drinks or other foods, then divide the remaining amount by the carbohydrate in each gel.
For example, you expect to run for two hours and have rehearsed a target of 40 g/hour. That means organising 80 g in total. Four gels containing 20 g each provide that amount if there are no other sources.
This is a worked calculation, not a universal half marathon prescription.
| Example for 2 hours | Total carbohydrate | From drinks | Remaining amount in 20 g gels |
|---|---|---|---|
| Target of 30 g/hour | 60 g | 0 g | 3 gels |
| Target of 40 g/hour | 80 g | 0 g | 4 gels |
| Target of 40 g/hour | 80 g | 20 g | 3 gels |
If your gels contain 25 or 40 g, the packet count changes. If your drink contains carbohydrate, include it. The same number of packets can represent very different strategies.
Plan timing in minutes first
Distance markers depend on pace. A runner at 4:30 min/km reaches kilometre 10 much earlier than a runner at 6:30. Build the timing plan first, then check where aid stations fit.
An illustrative schedule for four 20 g gels during a two-hour race might be minutes 20, 45, 70 and 95. It supplies 80 g overall, averaging 40 g/hour. This is a logistical example to rehearse; research does not establish those exact minutes as optimal.
You can adjust the schedule around aid stations. Follow the product’s instructions about water: gel formats and concentrations differ.
More carbohydrate is not automatically a better plan
Jeukendrup’s review explains how recommendations vary with exercise duration and carbohydrate type. Higher intakes and combinations using different intestinal transporters can be relevant in much longer events. That does not make 90 g/hour an automatic goal for a first half marathon. Carbohydrate intake during exercise.
Before increasing intake, ask whether the event needs that change and whether you can consume it comfortably. An unpractised high number creates additional uncertainty.
Rehearse the strategy before race day
Training the Gut for Athletes describes gastrointestinal adaptability and the value of practising intake during training. Responses remain individual; practice does not guarantee that symptoms disappear. Jeukendrup, 2017.
Write down the following before a suitable training session:
- Expected duration and conditions.
- Product and carbohydrate per serving.
- Timing and access to water.
- Carbohydrate from drinks, if any.
- Digestive comfort and how easy the packets are to carry and open.
Keep the record afterwards. Do not blame every symptom on a brand without reviewing breakfast, total intake and conditions.
Errors a simple calculation can catch
Copying “two gels” without checking grams. Two 20 g packets and two 40 g packets supply very different totals.
Forgetting the drink. If the planned total was 80 g and the drink adds another 30 g, actual intake becomes 110 g. That may be intentional, but it should appear in the plan.
Using an optimistic finish time. Review expected duration against recent preparation. Runi’s two-hour half marathon guide helps with splits, not with an individual nutrition prescription.
Scope of this article
Tables and timing examples are original calculations, not validated clinical protocols. This is education for healthy adults; medical conditions or persistent digestive symptoms need individual advice.