Ultra marathon fuel calculator
Plan fuel for 50K, 50 mile, 100K, 100 mile, or custom ultra distances. The calculator uses Mavr's ultra race categories to estimate carb cadence, hydration, sodium, caffeine, and course-aware aid-station timing.
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General guidance for healthy adults, not medical advice. Talk to a doctor or registered dietitian if you have a health condition, take medicines or have special dietary needs. Caffeine advice is for healthy adults only. EFSA's safe limit is 200 mg in one dose and 400 mg in a day.
How to use this calculator
Calculate an ultra marathon fueling plan from a 50K, 50 mile, 100K, 100 mile, or custom ultra distance, then adjust pace, gel product, carb target, body metrics, weather, and sweat profile.
Start with the race distance, then personalize the plan around the fuel you actually use in training.
- 1Choose 50K, 50 mile, 100K, 100 mile, or custom ultra as the race type.
- 2Enter target pace, gel carbs, body metrics, heat, sweat rate, and sweat saltiness.
- 3Generate the plan to review fuel cadence, total carbs, fluid, sodium, caffeine, and pre-race carb targets.
How the plan is built
- Ultra plans should be rehearsed in long runs because GI tolerance, terrain, and pace variability matter more over long durations.
- For course-connected ultras, verify drop bags, crew access, refill points, and aid-station inventory before race day.
- Use the carb override if your trained gut can handle a higher target or if your coach has prescribed a specific intake.
Fuel calculator FAQ
Quick answers for race-day carbs, gel timing, hydration, and distance-specific fueling decisions.
How much fuel do I need for an ultra marathon?
Many ultra runners target 60 to 90 grams of carbs per hour, while highly trained guts may work toward 100 to 120 grams per hour for very long events. The calculator estimates the total from your expected duration and chosen carb target.
Can I use this for 50K, 50 mile, 100K, and 100 mile races?
Yes. The website calculator now includes fixed ultra presets for 50K, 50 mile, 100K, and 100 mile races, plus a custom ultra distance option for events 45 km and longer.
Should an ultra plan include more than gels?
Usually yes. Gels can anchor carb cadence, but long ultras often need drink mix, chews, sodium, water refill planning, and sometimes savory foods or protein depending on duration and gut tolerance.