Marathon Fueling Calculator
How many gels do you need for a marathon? Enter your run time, carb target, and gel size. Account for sports drinks and download a timed fueling plan.
These values show an example. Use a carbohydrate target you have practiced.
Use the target you plan to practice or have already practiced.
Use grams of carbohydrate from the label, not the gel’s total weight.
Enter 0 if your drinks contain no carbohydrate.
Pack for the run
30 g of carbohydrate per gel, over 4:00:00.
- Your target
- 240 g
- Planned total
- 240 g
- Included from drinks
- 0 g
- Planned per hour
- 60 g/h
The entered gels and drinks meet your carbohydrate target.
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Your gel schedule
Times are measured from the start. Gels are spaced evenly; adjust around the course and the routine you have practiced.
View all 8 gel times
Gel 1
0:15:00
Gel 2
0:45:00
Gel 3
1:15:00
Gel 4
1:45:00
Gel 5
2:15:00
Gel 6
2:45:00
Gel 7
3:15:00
Gel 8
3:45:00
This plans carbohydrate from your entries. Water, sodium, caffeine, and pre-race food need separate planning. Practice your fueling before race day.
Work out what to pack and when to use it
Use the carbohydrate target you have practiced in training and the grams listed on your gels. If you also use a sports drink, include those carbohydrates so the same target is not counted twice.
Set the total carbohydrate target
Multiply your expected time in hours by your chosen grams per hour. Your target is an input; the calculator does not choose it for you.
target grams = run hours × grams per hour
Subtract the drink contribution
Enter the carbohydrate you plan to get from drinks each hour. The remaining grams are covered by gels. Any brand works if you know the carbohydrate amount on its label.
gels = round up((target grams − drink grams) ÷ grams per gel)
Check the rounded plan
Whole gels can put the total a little above your target. Both numbers are shown. The schedule spaces the gels evenly through the run, with the first at the midpoint of the first interval and none added at the finish.
Example: four hours, 60 g/hour, 30 g gels
The target is 240 g. If drinks provide 30 g/hour, they cover 120 g, leaving four 30 g gels. The evenly spaced gel times are 0:30, 1:30, 2:30, and 3:30. Change any input to match the products and plan you have practiced.
Common questions
How many gels do I need for a marathon?
It depends on your time, carbohydrate target, gel size, and other fuel. For a four-hour run at an entered target of 60 g/hour, eight 30 g gels cover 240 g if you use no other carbohydrates. Drinks or food reduce the amount the gels need to cover.
How many carbohydrates per hour should I enter?
Enter a target you can tolerate and have practiced. Burke and colleagues’ sports-nutrition review describes 30–60 g/hour for longer exercise and up to 90 g/hour for events lasting more than 2.5 hours, with carbohydrate type and individual tolerance affecting the plan. These ranges are context, not a personal prescription.
Does this include pre-race food, water, sodium, or caffeine?
No. The totals cover carbohydrate during the run from the gels and drinks you enter. Plan pre-race food, hydration, sodium, and caffeine separately; those needs cannot be inferred from a gel count.
Why does my plan contain more carbs than my target?
The calculator rounds up to whole gels. A 240 g target with 25 g gels needs ten gels, giving 250 g in total. The result shows the actual grams per hour after rounding.
Can I use this for a half marathon or a long run?
Yes. Enter the expected duration of that run and your practiced target. The arithmetic depends on time and your chosen products, so it also works without a race distance.
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