Calculate exactly how many gels you need for your marathon or half marathon. Get a personalized fueling schedule with 60-90g/hr carb targets, timing recommendations, and avoid hitting the wall.
Targets scale with race distance and duration: a 10K baseline of 30g/hr rises to 45g/hr for a half and 75g/hr for a marathon, and body weight raises the floor (0.7g of carbohydrate per kg per hour). Marathons cap at 100g/hr — the practical ceiling of glucose plus fructose co-ingestion — and shorter races at 90g/hr.
| 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 |
| Elapsed | Approx. distance | Carbs | Suggestion |
|---|---|---|---|
| 0:15 | 2.6km | 33 g | 1-2 gels or mixed fuel |
| 0:32 | 5.6km | 33 g | 1-2 gels or mixed fuel |
| 0:49 | 8.6km | 33 g | 1-2 gels or mixed fuel |
| 1:06 | 11.6km | 33 g | 1-2 gels or mixed fuel |
| 1:23 | 14.6km | 29 g | 1-2 gels or mixed fuel |
| 1:48 | 19.0km | 29 g | 1-2 gels or mixed fuel |
| 2:13 | 23.4km | 29 g | 1-2 gels or mixed fuel |
| 2:38 | 27.8km | 29 g | 1-2 gels or mixed fuel |
| 3:03 | 32.2km | 29 g | 1-2 gels or mixed fuel |
| 3:33 | 37.5km | 29 g | 1-2 gels or mixed fuel |
Fueling is front-loaded: stops start at 15 minutes and repeat every ~17 minutes early, stretching to 25 and then 30 minute intervals as the race goes on, and stop about 15 minutes before the finish because nothing taken later will be absorbed in time.
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.