Race Fueling Calculator
60g/h
10gels
Auto 60 g/h · 60–90 band
Train the gut. Planning aid, not medical advice.
Gel size
- Total carbs
- 240g
- Gels
- 10
- Interval
- 22:00
Fuel band
Gel 1
25 g carbs
Gel 2
25 g carbs
Gel 3
25 g carbs
Gel 4
25 g carbs
Gel 5
25 g carbs
Gel 6
25 g carbs
Gel 7
25 g carbs
Gel 8
25 g carbs
Gel 9
25 g carbs
Gel 10
25 g carbs
First gel at 24:00 elapsed; last gel 18:00 before the finish. Marks are even in that window. Skip the last window so you are not taking a gel on an empty stomach at the line. Gel size chips are carbohydrate grams per packet — examples, not a brand lock-in.
Train the gut on long runs. This is a planning aid from duration-based carb ranges, not a lab prescription and not medical advice.
Hydration (optional)
Secondary to carbs. Sip to thirst. A commonly cited starting range is ~14–27 fl oz/h, not a target you must hit. Sweat rate varies. Not medical advice.
Calories burned · Marathon pace · Half marathon pace · Race time predictor · Split calculator · 50K pace · 50 mile pace · 100 mile pace · 100K pace.
Worked examples
Marathon 4:00:00 · 25 g gel · Auto
60 g/h · 240 g · 10 gels · band every 22:00 after 24:00
Half 2:00:00 · 25 g gel · Auto
45 g/h · 90 g · 4 gels
10K 50:00 · 25 g gel · Auto
15 g/h · ~12.5 g · 1 gel · water first
Marathon 3:00:00 · 25 g gel · Auto
60 g/h · 180 g · 8 gels
Marathon 4:00:00 · 40 g gel · Auto
60 g/h · 240 g · 6 gels
Formulas
Planning aid from duration-based carb ranges, not a lab prescription and not medical advice. Auto picks a single number inside each band. Totals are even arithmetic: carbs = g/h × hours; gels = ceil(carbs ÷ grams per gel). The fuel band starts 24 minutes in and stops 18 minutes before the finish so the last window is empty near the line. Intakes above about 60 g/h usually need more than one carbohydrate (glucose + fructose). This page does not model product chemistry.
- < 1.0 h → Auto 15 g/h (0–30 band · water first)
- 1.0–2.5 h → Auto 45 g/h (30–60 band)
- ≥ 2.5 h → Auto 60 g/h (60–90 band)
- carbsTotal = targetGPerHour × durationHours
- gelCount = ceil(carbsTotal / gelCarbs)
Duration bands follow common sports-nutrition guidance for endurance events (ISSN position stand; ACSM). Individual gut training, heat, and product mix change what you can absorb. Calories burned · marathon pace · half pace · predictor · splits.
FAQ
How many gels for a marathon?
On this page, a 4:00:00 marathon at Auto is 60 grams of carbohydrate per hour, 240 g total. At 25 g per gel that is 10 gels. A 3:00:00 marathon is 180 g, or 8 gels at 25 g. Switch gel size to 40 g and a 4:00 marathon is 6 gels. Train the gut; this is not medical advice.
How many carbs per hour should I eat while running?
Auto uses duration bands: under 1 hour, 15 g/h (midpoint of 0–30, water first); 1.0–2.5 hours, 45 g/h (mid of 30–60); 2.5 hours and longer, 60 g/h (low end of 60–90). Override 30–60 or 60–90 if you already train a different gut target. Intakes above about 60 g/h usually need glucose plus fructose.
How many gels for a half marathon?
A 2:00:00 half at Auto is 45 g/h, 90 g total, and 4 gels at 25 g each. That is the middle of the 30–60 g/h band for 1–2.5 hour races. Type a different finish time to rescale.
Do I need gels for a 10K?
Usually no. A 50:00 10K is under 1 hour, so Auto stays water-first at 15 g/h (~12.5 g, 0–1 gel). Do not invent aggressive fueling for a sub-hour race. Carry water; a gel is optional.
What is a running fueling calculator?
A race fueling calculator turns expected finish time into a carbs-per-hour target and a gel count. SplitLab uses even arithmetic from published duration bands, then spaces gels from 24 minutes in through 18 minutes before the finish. It is a planning aid, not a lab prescription.
Is this medical advice?
No. It does not diagnose GI issues, pick a brand, or replace a sports dietitian. Practice the same products and timing on long runs that you plan to use on race day.