Race Fuelling Guide: How Many Carbs and Gels You Actually Need
Runward —
Most runners do not lose time in a race because they were undertrained. They lose it in the last third because they ran out of usable fuel. Fuelling is the cheapest performance gain available to you, and it only takes one afternoon to plan.
Why you run out of energy
Your muscles and liver store roughly 400–500 g of carbohydrate (about 1,600–2,000 kcal) when fully loaded. Running burns roughly 60 kcal per kilometre for a 70 kg runner, so a marathon costs around 2,500 kcal — more than the tank holds. Fat covers part of it, but fat cannot be burned fast enough at race pace. When carbohydrate availability drops, pace drops with it. That is the wall.
For a 10K the tank is never the problem. For a half it becomes relevant. For a marathon it decides your result.
Carbohydrate targets by distance
| Distance | During-race carbs | Practical plan |
|---|---|---|
| 10K | None needed | Small carb snack 1–2 h before, water only in the race |
| Half marathon | 30–60 g per hour | 1–3 gels, sports drink at aid stations |
| Marathon (sub-3:30) | 60–90 g per hour | 5–8 gels, start by 40 min, every 25–35 min |
| Marathon (3:30–5:00) | 45–75 g per hour | 5–7 gels plus drink carbs, steady spacing |
Going above 60 g per hour requires a mix of glucose and fructose (most modern gels and drink mixes already use both) and a trained gut. Do not attempt 90 g per hour for the first time on race day.
Fluid and sodium
Drink to thirst rather than to a fixed schedule, aiming for roughly 400–800 ml per hour in temperate conditions and more in heat and humidity. Sodium needs sit around 300–700 mg per litre of fluid; heavy and salty sweaters sit at the top of that range. Sports drinks, salt capsules or salted gels all work — the source matters less than consistency.
A simple check: weigh yourself before and after a long run. Losing more than 2–3% of body weight means you were under-drinking.
Build your plan with the calculator
Rather than guess, put your distance, goal time and body weight into the Runward nutrition calculator and it returns your hourly carb target, total carbs, gel count and a timing schedule.
Open the Race Nutrition Calculator →
You can also plan your target race paces on the same page with the pace, level and equivalents tool, and tick off your kit with the printable race day checklist.
The three days before
- Increase carbohydrate to roughly 7–10 g per kg of body weight per day for the final 2–3 days, mostly by adding rice, pasta, bread, potatoes and fruit juice rather than eating larger meals.
- Cut back on high-fibre and very fatty foods on the last day to keep your gut calm.
- Expect to gain 1–2 kg. That is stored glycogen and water, and it is a good sign.
Race morning
Eat 1–4 g of carbohydrate per kg of body weight, 2–3 hours before the gun — something familiar and low in fibre and fat. Sip 400–600 ml of fluid in that window, then a small amount 15 minutes before the start. Take a gel 5–10 minutes before the gun if the race is a half or longer.
In-race execution
- Start fuelling early — by 30–40 minutes, before you feel you need it.
- Space gels evenly, every 20–35 minutes, rather than clustering them late.
- Take gels just before an aid station so you can wash them down with water.
- Never mix a full-strength sports drink with a gel at the same moment if your stomach is sensitive; alternate instead.
- If nausea starts, slow slightly, take fluid only for a few minutes and then resume. Abandoning fuelling entirely almost always ends the race worse.
Train your gut
Your gut adapts like any other system. Use two or three long runs per training block to rehearse race fuelling exactly: same products, same intervals, same paces. If a product causes trouble twice, change the product, not the plan.
Common mistakes
- Fuelling only when you feel bad. By then you are 20–30 minutes behind and cannot catch up.
- Trying a new gel on race day. Race day is for rehearsed products only.
- Over-drinking plain water. Large volumes without sodium dilute blood sodium and cause bloating and worse.
- Ignoring caffeine tolerance. Caffeinated gels help, but keep the total in a range you have tested — typically 3 mg per kg across the race.
Take it further
The paces, carb targets and gel timing in this guide are population averages. The Runward app narrows them to you by using your actual training data — recent long runs, sweat and pace trends, and race predictions — so the plan you rehearse is the plan you race.