Marathon Fueling Calculator

Marathon fuel calculator. Enter your finish time to calculate carbs per hour, total carbs needed, and how many gels to carry on race day.

Calculate your marathon fuel needs in seconds. Enter your finish time to get carbs per hour, total carbs, and gel count — personalized to your race.

Personalized carbs/hour calculation
Total gel count based on your finish time
Works for any marathon goal from 2:30 to 6+ hours

How to calculate marathon fuel needs

Enter your marathon finish time and get personalized carb and gel numbers.

Enter finish time: Use your realistic marathon goal time or a recent race result.
Get your numbers: See carbs/hour, total carbs, and gel count calculated instantly.
Plan your carry strategy: Decide how many gels to carry vs pick up at aid stations.

Frequently asked questions

What is the difference between a fuel plan and a fuel calculator?

A calculator gives you the numbers (carbs/hour, gel count). A plan adds timing and scheduling on top. This tool does both — start with the math, then build your schedule.

How many carbs do I need for a 4-hour marathon?

At 60g/hour, that is 240g total (about 8-10 standard gels). At 90g/hour, that is 360g total. Most runners land somewhere in between based on gut training.

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.