The short answer
For a four-hour marathon at a rehearsed 60 g carbohydrate per hour, with 25 g gels and no other carbohydrate, the arithmetic is 4 × 60 ÷ 25 = 9.6: round up to ten gels. If drinks or chews supply carbohydrate, subtract those grams first. Ten gels is this example's answer, not a universal marathon rule.
Choose an intake you have practised and can tolerate, then calculate the products and timing. Distance-running nutrition guidance emphasises an individual plan that balances intake with practical opportunities and gut comfort.1
The gel-count formula
total planned race carbohydrate = finish hours × practiced grams per hour
grams to supply from gels = max(0, total planned race carbohydrate − other race carbohydrate)
gels to consume = round up(grams to supply from gels ÷ grams per gel)
Count carbohydrate from all during-race sources: gels, drinks, chews, and food. Do not subtract breakfast from the during-race total; it is a separate part of the plan. Check the exact packet label because products differ in size, carbohydrate, caffeine, and fluid instructions.
The formula estimates supplies. It does not tell you what your carbohydrate target should be, guarantee absorption, or prescribe a hydration volume.
Gel counts by finish time
The table assumes 25 g carbohydrate per gel and no carbohydrate from drinks or other food. Each result rounds upward. It excludes an optional backup packet, which you carry but do not automatically consume.
| Finish time | 45 g/hour | 60 g/hour | 75 g/hour |
|---|---|---|---|
| 3:00 | 6 | 8 | 9 |
| 3:30 | 7 | 9 | 11 |
| 4:00 | 8 | 10 | 12 |
| 4:30 | 9 | 11 | 14 |
| 5:00 | 9 | 12 | 15 |
The columns are calculation scenarios, not recommendations based on finishing speed. A slower runner does not automatically need a higher hourly rate. A five-hour race at 45 g/hour requires 225 g, which is nine 25 g gels—not ten before adding a backup.
Worked example: count sports drink before packing gels
Suppose your rehearsed four-hour plan is 60 g/hour: 240 g total. You expect to consume two measured servings of a tested drink, each providing 30 g carbohydrate. That is 60 g from drink and 180 g remaining from gels.
With 25 g gels, 180 ÷ 25 = 7.2, so eight complete packets supply 200 g. Eight gels plus those drinks provide 260 g, or 65 g/hour over four hours. Rounding changes the intake; check that the resulting plan is one you have rehearsed rather than blindly treating eight as exact.
You could instead adjust the product mix or portions to fit the intended total. Do not reduce necessary fluid merely to make the carbohydrate arithmetic tidy. If on-course cups are unmeasured or product concentration is uncertain, do not count their carbohydrate as guaranteed. Record that uncertainty and plan a practical backup.
Turn the total into a schedule
For a gel-only calculation, minutes between gels = 60 × grams per gel ÷ target grams per hour.
At 25 g per gel and 60 g/hour, this gives 25 minutes. That is an average interval to rehearse, not an instruction to swallow a gel whenever an alarm rings regardless of symptoms or product directions.
Four-hour, gel-only packing example
A ten-gel schedule could use elapsed minutes 10, 35, 60, 85, 110, 135, 160, 185, 210, and 235. Ten 25 g gels supply 250 g, averaging 62.5 g/hour over four hours. A spare packet is separate.
If you finish earlier, miss a packet, change products, or add sports drink, the total changes. Do not take remaining packets after finishing just to complete the schedule. This example is arithmetic, not a tested protocol or an individual nutrition prescription.
Choose a carbohydrate target before choosing a brand
Sports nutrition guidance commonly discusses 30–60 g/hour for prolonged exercise and higher rates, including around 75–90 g/hour, in longer events when appropriate and tolerated.1, 2, 3 Those ranges are context, not a requirement to jump to the highest number. Higher intake strategies also depend on carbohydrate formulation and execution.
Discuss individual targets with a sports dietitian when you have recurrent gastrointestinal symptoms, relevant medical conditions, or uncertainty about adequate fueling. Do not turn a population recommendation into a race-week experiment. Use the 30–60–90 guide for the separate target-selection discussion.
Rehearse the plan without turning every long run into a test
Use suitable long runs already in your programme. Keep running demand appropriate and change one nutrition variable at a time. Record the product, amount, timing, other food or drink, conditions, and symptoms.
Research on training the gut suggests adaptation is possible, but it does not guarantee that every runner can tolerate every intake or product.4 Evidence on carbohydrate feeding during endurance exercise supports benefits in some settings while showing variation across studies.5 Successful rehearsal is more useful than copying an elite athlete's product list.
A useful record is: “Four packets, one measured drink serving, mild fullness after packet three, difficult to open with wet hands.” That identifies both intake and practical problems. “Fueling went badly” does not tell you what to change.
Hydration, caffeine, and sodium are separate calculations
Follow the product's fluid directions and your rehearsed hydration approach. A gel schedule does not reveal sweat losses or make a fixed amount of water appropriate. Fluid guidance emphasises individual needs; overdrinking can also be dangerous.6, 7
If using caffeine, count the total across gels, drinks, coffee, and other products. Caffeine research describes benefits and individual differences, but more is not automatically better.8 This guide does not prescribe a dose. Keep any caffeine strategy familiar and seek professional guidance when relevant to your health or medication.
Do not assume sodium in a gel prevents problems caused by excessive fluid intake. Use the hydration worksheet to organise a separate rehearsal, not to force every gel to match an arbitrary cup count.
What if the plan breaks down?
A missed packet is not a reason for a large catch-up dose. Reassess effort, symptoms, remaining time, and what you have already consumed. Do not force more food or fluid through worsening nausea or vomiting.
Confusion, collapse, severe weakness, chest pain, severe breathing difficulty, or persistent vomiting warrants medical assistance. Do not assume these symptoms are simply dehydration and keep racing while drinking more. Stop and use on-course medical support when needed.
Race-week packing checklist
- Record realistic finish time and the rehearsed hourly intake.
- Count all planned carbohydrate sources and verify labels.
- Check official aid-station products and locations.
- Separate packets to consume from spare packets to carry.
- Rehearse opening and carrying the products.
- Keep the hydration and caffeine notes separate.
- Change the plan if conditions, health, or expected duration change.
This guide is educational and not medical advice. 26weeks.ai helps organise preparation around your goal and actual training. Start training now.
References
Sources and associated claims reviewed October 17, 2026. Practical examples are editorial guidance, not independently validated protocols.
1 Contemporary Nutrition Strategies to Optimize Performance in Distance Runners and Race Walkers. (2019). Read the source.
2 American College of Sports Medicine Joint Position Statement. Nutrition and Athletic Performance. (2016). Read the source.
3 How and when do I use it? | ASC. Read the source.
4 Training the Gut for Athletes. (2017). Read the source.
5 The ergogenic effects of acute carbohydrate feeding on endurance performance: a systematic review, meta-analysis and meta-regression. (2024). Read the source.
6 American College of Sports Medicine position stand. Exercise and fluid replacement. (2007). Read the source.
7 Statement of the Third International Exercise-Associated Hyponatremia Consensus Development Conference, Carlsbad, California, 2015. (2015). Read the source.
8 Caffeine, CYP1A2 Genotype, and Endurance Performance in Athletes. (2018). Read the source.