How Many Gels Do You Need for a Marathon?
For a 3:30 marathon targeting 80g of carbs per hour, you need somewhere between 6 and 13 gels depending on the brand. That's a huge range, and it's why “just bring some gels” isn't a fueling plan.
The exact number depends on three things: your carb target per hour, the carbs per gel in your chosen brand, and whether you're supplementing with drink mix. I'll break all of this down, but here's the short version: most marathon runners should be taking in significantly more carbs than they think.
The old advice is wrong
For years, the standard recommendation was 30-60g of carbs per hour. You'll still see this in outdated nutrition guides and on the back of gel packets. The problem is it's based on research from the 1990s that only studied single-source carbohydrates (glucose alone).
Modern research on dual-source carbs (glucose + fructose) shows your gut can absorb far more: 90g, 100g, even 120g per hour if you've trained for it. This is the protocol behind virtually every major marathon course record in the last five years.
David and Megan Roche's 8-guideline framework, which is what FuelCenter's calculator is built on, puts the range at 75-90g/hr for moderate-to-hard efforts over 90 minutes. That's the baseline, not the ceiling. Experienced athletes who've trained their gut tolerance can push to 105-120g/hr.
I target 100-105g/hr in major workouts and raced the NYC Marathon at roughly 90g/hr for a 3:05 finish. The difference between fueling at 60g/hr (where I used to be) and 90g/hr was the difference between surviving miles 20-26 and actually racing them.
The math: how many gels you actually need
A 3:30 marathon at 80g carbs per hour. That's 3.5 hours × 80g = 280g of total carbs from gels (assuming no drink mix).
| Gel | Carbs/gel | Gels needed (280g) |
|---|---|---|
| Carbs Fuel | 50g | 6 |
| SiS Beta Fuel | 40g | 7 |
| Maurten Gel 160 | 40g | 7 |
| Precision PF 30 | 30g | 10 |
| Maurten Gel 100 | 25g | 12 |
| GU Roctane | 25g | 12 |
| Tailwind | 25g | 12 |
| Clif Shot | 24g | 12 |
| GU Energy Gel | 22g | 13 |
| Spring Energy | 20g | 14 |
The spread is massive. 6 Carbs Fuel gels versus 14 Spring Energy gels for the same carb target. This is why gel choice matters. It's not just about flavor preference. It's about how many packets you're physically carrying and consuming over 26.2 miles.
Adjusting for your goal time
The 3:30 example is just one scenario. Here's how the total carb target shifts with finish time (at 80g/hr):
| Finish time | Total carbs | SiS (40g) | GU (22g) | Maurten 100 (25g) |
|---|---|---|---|---|
| 3:00 | 240g | 6 | 11 | 10 |
| 3:15 | 260g | 7 | 12 | 11 |
| 3:30 | 280g | 7 | 13 | 12 |
| 3:45 | 300g | 8 | 14 | 12 |
| 4:00 | 320g | 8 | 15 | 13 |
| 4:30 | 360g | 9 | 17 | 15 |
| 5:00 | 400g | 10 | 19 | 16 |
Slower marathons require more total carbs simply because you're out there longer. A 5-hour marathoner at 80g/hr needs 400g. That's 19 GU gels. Nobody wants to eat 19 of anything during a race. This is where higher-carb gels and drink mix become essential.
Drink mix changes the equation
You don't have to get all your carbs from gels. A drink mix in your handheld or hydration vest can cover 20-40g per hour, which dramatically cuts your gel count.
Same 3:30 marathon at 80g/hr. If your drink mix provides 30g/hr (105g total over 3.5 hours), you only need 175g from gels. That drops a GU count from 13 to 8. Much more manageable.
This is the approach I use. I run with a concentrated drink mix that covers about a third of my carb target, then fill the rest with gels. Fewer gels means fewer stops to open packets, fewer chances for your stomach to protest, and less garbage to carry.
What about the experience factor?
Not everyone should jump to 80g/hr on their first marathon. Your gut needs to be trained just like your legs.
If you're new to structured fueling, start at 60g/hr in training and work your way up over 6-8 weeks. Practice on your long runs. Your stomach will adapt. Most runners can get to 75-90g/hr within a training block if they're consistent about practicing.
If you've been training with high-carb fueling and your gut handles it well, push toward 90-100g/hr on race day. The science supports it, and the performance difference is real.
The worst thing you can do is try a new carb target on race day without training for it. The second worst thing is sticking with 30-60g/hr because that's what you've always done.
The bottom line
Count your carbs, not your gels. Figure out your target carbs per hour (75-90g minimum for marathon effort), multiply by your expected finish time in hours, then divide by your gel's carb content. That's your number.
Or skip the math entirely and let FuelCenter do it. The calculator factors in your duration, intensity, experience level, gel brand, and drink mix to give you a minute-by-minute fueling plan with exact gel timing.
Build your marathon fueling plan
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Open Marathon Calculator →FAQ
How many gels should I take per hour during a marathon?
At 80g carbs per hour, that’s 2-4 gels per hour depending on the brand. With a 40g gel like SiS Beta Fuel, that’s one every 30 minutes. With a 22g gel like GU, that’s roughly one every 15-20 minutes.
Can you take too many gels during a marathon?
Your gut has a limit on carb absorption,roughly 90-120g/hr with dual-source carbs (glucose + fructose). Going above your trained tolerance can cause GI distress. The key is training your gut during long runs, not just hoping for the best on race day.
Should I use the same gel for the whole marathon?
You don’t have to. Many runners use a higher-carb gel (SiS Beta Fuel, Maurten 160) for the bulk of the race and switch to a caffeinated gel (Maurten Caf 100, GU Roctane) for the final 10K. Practice any gel you plan to race with during training.
When should I take my first gel in a marathon?
Within the first 20-30 minutes. Don’t wait until you feel like you need it,by then you’re already behind on carbs. Start fueling early and stay consistent throughout.
Is 30g of carbs per hour enough for a marathon?
No. 30g/hr was the old standard based on outdated single-source carbohydrate research. Modern evidence supports 75-90g/hr as the minimum for marathon-effort intensity, with experienced athletes benefiting from 100g/hr or more.
Do I need gels if I’m using a sports drink on course?
On-course sports drinks help, but most only provide 15-30g of carbs per serving. That’s not enough on its own. You’ll still need gels to hit your target, but the drink reduces the total number required.