How Many Gels for a Marathon?

How many gels do you need for a marathon? Use your finish time and carb target to estimate gel count and build a simple fueling schedule.

Gel count depends on race duration and carbs per gel. This page helps you estimate your total and turn it into a repeatable schedule.

Gel count estimate from finish time
Carbs/hour and total carbs
Pairs well with carb loading + hydration

How to estimate marathon gel count

Calculate gels needed by combining your finish time with a realistic carbs-per-hour target.

Enter finish time: Input your marathon goal time.
Set carb target: Use a target like 60-90g/hr based on experience.
Translate to gels: Convert total carbs into gels based on your product labels.

Frequently asked questions

How many gels is too many?

Too many is anything your gut can't tolerate. Practice in training and increase gradually; most issues come from going too high too soon.

How many grams of carbs are in a gel?

Most gels are ~20-30g carbs, but it varies by brand. Always check the label and plan around your actual products.

Fueling reference

Race-day carb targets and gel counts by finish time (baseline, no body weight entered)
Race	Finish time	Carbs/hour	Total carbs	Calories	Gels
Half marathon	1:20	45 g/hr	60 g	240 kcal	2
Half marathon	1:35	45 g/hr	71 g	284 kcal	3
Half marathon	1:50	45 g/hr	83 g	332 kcal	3
Half marathon	2:05	45 g/hr	94 g	376 kcal	4
Half marathon	2:20	45 g/hr	105 g	420 kcal	4
Marathon	2:50	75 g/hr	213 g	852 kcal	5
Marathon	3:15	75 g/hr	244 g	976 kcal	5
Marathon	3:45	75 g/hr	281 g	1124 kcal	6
Marathon	4:15	75 g/hr	319 g	1276 kcal	7
Marathon	4:45	75 g/hr	356 g	1424 kcal	7
Marathon	5:15	75 g/hr	394 g	1576 kcal	7

Other TrainPace tools

For AI agents

Every page on this site has a Markdown mirror at the same path with a .md suffix (for example /calculator.md), and honors an Accept: text/markdown request header on the HTML URL. The calculations here are also available as callable tools through a free public MCP server — no account or API key.