How Many Carbs Per Hour? A Guide for Runners & Triathletes

Ever faded in the last 10km and wondered why? Chances are it wasn't your legs - it was your fuelling. Get your carbs per hour right and you can hold your pace to the finish line. For most races over 75-90 minutes, that means 30-90g of carbs every hour¹,². Here's how to find your number - or skip the maths and let our carb calculator do it for you in under a minute.

Table Of Contents

• Why Carbs Per Hour Matters

• How To Use The Carb Calculator

• How Pace Comes Into It

• Other Considerations

• Carbs Per Hour By Finish Time

• FAQs

Why Carbs Per Hour Matters

Your muscles store enough glycogen for roughly 90 minutes of hard running. Past that, what you eat and drink on course is what keeps your pace from fading - the dreaded "bonk" or "hitting the wall".

Thinking in grams per hour (g/h) turns a vague "take some gels" into a plan: a target, a timing schedule, and a product list you can practise in training.

How To Use The Carb Calculator

1. Enter your event (Triathlon, Running, Swimming, Cycling, HYROX, Team, Sports/Other

2. Select your distance/duration)

3. You may be asked to select your gender

4. Get your carbs-per-hour target and recommended products
   
   

How Pace Comes Into It

Pace matters in two ways: it sets how long you'll be out there, and how fast you burn through carbs while you are.

• Faster pace = shorter race → A 1:45 half finisher has less time to run low on glycogen than a 2:30 finisher, so they need fewer total carbs - sometimes only 30-45g/h.

• Faster pace = higher burn rate → The harder you run, the more your body relies on carbohydrate over fat.1 Race-pace efforts burn carbs quickly, so fast runners in longer events (marathon and beyond) benefit from the top end of the range: 60-90g/h.

• Slower pace = longer exposure → A 5-hour marathoner burns carbs more slowly per hour but for longer. Total carbs matter more than hourly rate, and steady, regular intake beats big doses.

• Harder pace = touchier gut → At high intensity, blood flow is diverted from your gut to your muscles, so absorption drops.³ Faster runners should favour gels and drinks over solids, and practise race-pace fuelling.

In short: duration sets the target range, pace tells you where to sit within it.

Other Considerations

• Gut training → Your gut adapts. If you've never taken more than one gel per run, don't jump straight to 90g/h on race day. Build up by 10-15g/h every week or two in your long runs. Stop increasing carbs if you get any gut symptoms.

• Carb type → Above about 60g/h, choose products that mix glucose and fructose (often listed as maltodextrin and fructose). They use separate absorption pathways, so you can absorb more with less stomach upset.¹,²

• Body size → Unlike daily nutrition, carb needs during racing don't scale much with body weight - your gut's absorption limit is the bottleneck.¹ Use weight as a nudge, not a formula.

• Heat and humidity → Hot races raise carb burn and fluid needs, and can make the gut more sensitive.³  Drinks and electrolyte-plus-carb mixes help you cover fuel and fluid together.

• Fluid with your fuel → Take gels with water. Concentrated carbs without water can cause cramping and nausea.³ 

• Caffeine → Caffeine taken before or during the race can reduce perceived effort and lift performance in the back half.4 Stick to products and doses you've used in training.

• Mix your formats → Gels, chews, drink mixes and bars all count. Most athletes do best combining two or three to avoid flavour fatigue.

• Course logistics → Check what's on offer at aid stations and where. Carry what you need between them, or plan your own fuel entirely if you're unsure.

Carbs Per Hour By Finish Time

Use this as a starting point, then fine-tune in training.¹,² Gels contain anywhere from 20g of carbs to 50g of carbs per gel - check your product's label.

Sub-2 half marathon

• Aim for 30-60g/h. Faster runners (sub-1:40) can sit at the low end; closer to 2:00, aim higher.

• Take your first gel at 30-40 minutes, then every 25-30 minutes.

• Keep it simple: Take a gel just before an aid station, then wash it down with water. Solids are rarely worth it at this pace.

• Many runners skip fuelling in a half. Don't - the last 5km is where it pays off.

4-hour marathon

• Aim for 60-90g/h. Over a full marathon, fuelling is make-or-break.

• Start early: first fuel at 20-30 minutes, then every 20-25 minutes. Don't wait until you feel flat.

• Use glucose-fructose products to reach the 60-90g/h end comfortably.

• Combine gels with a carb drink to spread the load and ensure adequate fluid absorption.

• If caffeine sits well with you, save caffeinated gels for the final 15km.

5-hour-plus marathon

• Aim for 60-75g/h, taken little and often (every 15-20 minutes).

• At this pace, your gut usually copes well. Chews, bars and real food work alongside gels.

• Use walk breaks to eat and drink calmly.

• Flavour fatigue is real over 5+ hours. Pack a mix of sweet, salty and neutral options.

• Total carbs add up: plan your carry and use aid stations to restock.

Triathlon: 70.3 & Ironman

In triathlon, the bike is your main fuelling window. It's easier on the gut than running, so front-load your carbs there and top up on the run.

• Start fuelling 10-15 minutes into the bike, once your heart rate settles after the swim and T1.

• Use bottles for a base load. A carb drink mix on the bike covers fluid and 30-60g/h, with gels or bars on top.

• Some Well-trained athletes can push to 90-120g/h on the bike, but only after weeks of gut training.²

• Ironman needs more variety. Over 10+ hours, you may want to include some solid food on the bike and expect your run intake to drop off - bank carbs early, but keep your sodium intake steady.

FAQs

Do I need carbs for a 10km or a race under an hour? Usually not. A good pre-race meal covers it. A gel 10-15 minutes before the start is plenty.

What if my stomach can't handle that much? Start at the low end (30-40g/h) and build in training. Choose gut-friendly products and take them with water.

Do sports drinks count? Yes. Check the label for grams of carbs per serve and include them in your hourly total.

Is more always better? No. Above 90g/h, extra benefit for most athletes is unproven.² and stomach issues become more likely.

Ready To Build Your Plan?

Try the Aid Station carb calculator to get your personal carbs-per-hour target and recommended products. Got a nutrition question? Our in-house dietitian, Ash Miller, is always happy to help through the Ask Ash page.

Ash Miller
Dietitian and Nutritionist (Masters)
Bachelor of Physical and Health Education
Instagram: @ashthomo_nutrition

References

1. Jeukendrup A. A step towards personalized sports nutrition: carbohydrate intake during exercise. Sports Medicine, 2014.

2. Dietary carbohydrate and the endurance athlete: contemporary perspectives. Gatorade Sports Science Institute, Sports Science Exchange #231.

3. Jeukendrup A. Training the gut for athletes. Gatorade Sports Science Institute, Sports Science Exchange.

4. Guest NS, et al. International Society of Sports Nutrition position stand: caffeine and exercise performance. Journal of the International Society of Sports Nutrition, 2021.

Disclaimer:
The content in this article is for general information only and is not a substitute for professional medical advice, diagnosis, or treatment. Always speak with your doctor or allied health team before changing your diet, exercise, or taking supplements, especially if you have a health condition or take medication. Please use this information as a guide only. Aid Station doesn't take responsibility for individual outcomes.