Marathon Fueling Strategy: Grams per Hour, Not per 6 km

A marathon fueling strategy is a plan for how many grams of carbohydrate you take per hour, in what form, and at which points of the course, practised in training before race day. Published guidance starts first-timers at 30 to 60 grams per hour and lets faster, gut-trained runners go higher. The detail most plans skip: a schedule written in kilometres delivers a very different hourly dose to a 2:30 runner than to a 4:30 runner, so the plan has to be built from your finish time, not copied.

The three numbers a fueling plan has to fix

Carbohydrate per hour. Kelly Hogan, quoted in a guide published by UConn's College of Agriculture, Health and Natural Resources, puts the starting point at "30 to 60 grams of carbohydrates per hour", with fueling starting 30 to 45 minutes into the run for most people (UConn / Korey Stringer Institute). The same guide quotes Douglas Casa: "a gram of sodium per liter is generally a good amount."

Interval. Maurten's marathon fuel guide lists target bands by finish time, from 70 to 80 g/h for sub-2:30 down to 39 to 44 g/h for sub-4:30, and its standard plan is "Six Gels, one every 6k" (Maurten Fuel Guides).

Total. Hours on the course multiplied by grams per hour. This is the number that decides how many gels, chews or bottles you carry.

What happens before the start

Carbohydrate loading is a separate step from in-race fueling. Louise Burke's review for well-trained marathoners describes intakes of 10 to 12 g per kg of body mass per day over the 36 to 48 hours before the race, combined with a taper (Burke, 2007). The in-race plan builds on top of that; it does not replace it.

Why a per-kilometre schedule changes with your pace

"One gel every 6 km" sounds like a fixed dose. It is not. The time between gels depends on pace, and so does the carbohydrate you actually take in per hour.

The following worked example assumes 25 g of carbohydrate per gel purely for the arithmetic (check the label of the product you use) and six gels taken at 6, 12, 18, 24, 30 and 36 km, which is 150 g in total:

The same six gels give the 2:30 runner 60 g/h across the race and the 4:30 runner 33 g/h, close to half. A 4:30 runner who copies a faster friend's "every 6k" plan sits at the bottom of the 30 to 60 g/h starting range, while a 2:30 runner using the same plan is already at 60.

Converting a target rate into a gel count

Run the calculation the other way round. Example: a 4:00 target at 45 g/h needs 4 × 45 = 180 g. At 25 g per gel, that is 7.2 gels, so seven gels plus a carbohydrate drink, or eight gels. The same 4:00 runner at 30 g/h needs 120 g, which is about five gels. The gap between the two ends of the starting range is three gels, which is why the per-hour number has to be chosen deliberately and tested.

What typically goes wrong

The plan is never rehearsed. The UConn guide is direct: practising fueling on long runs before the race is "so, so important", and "You don't want to introduce anything new to your body when you toe the line." Maurten's guide makes the same point about building a personal plan in training. A gut that has never handled 60 g/h during a run is not a safe place to discover its limit at kilometre 30.

Gels without water. Plans often place gels where it is convenient on the clock, not where fluid is available. Check the race's official aid-station list and shift each gel to the nearest station.

Starting too late. Waiting until the first sign of fatigue wastes the early window. Hogan's 30 to 45 minute start point is a concrete rule to test against your own experience.

Copying a rate from a faster runner. The table above shows how far a per-distance plan drifts with pace. Recalculate for your own finish time.

Building the plan over the winter long runs

For runners targeting a spring marathon, the long runs from November onwards are where the fueling plan gets tested. A practical sequence:

1. Pick a starting rate inside the 30 to 60 g/h range.
2. Translate it into a timed schedule for your long-run pace, not race pace: minutes between intakes, grams per intake.
3. Write down what you took, when, and how your stomach responded. Note the temperature, because a cold December long run is a different test from a warm race morning.
4. Adjust one variable at a time: rate, product, or timing.
5. Before race week, rebuild the schedule for your target race pace and map each intake to an aid station.

Your race pace and split targets are the input for step 5. Marathon splits calculator: break down your goal pace by distance shows how to get clock times per kilometre, and those clock times are what turn a distance-based fuel plan into a time-based one.

How TrainingFlow handles this

Every TrainingFlow race strategy includes a carbohydrate, fluid and sodium timeline alongside the pacing plan, calculated from the predicted race duration. The engine raises the hourly carbohydrate target in steps as the expected race time gets longer and caps it by the experience level you enter, so a first-time marathoner is not handed the ceiling that suits a gut-trained runner. Your first race strategy is free; further races cost €7 each or €19 per year for unlimited strategies, according to TrainingFlow's pricing page. The timeline is a starting point to test on long runs, not a substitute for advice from a sports dietitian if you have digestive problems or a medical condition.

FAQ

How many gels for a 4 hour marathon?

It depends on the hourly rate you have tested and the carbohydrate per gel. In the example above, a 4:00 runner at 45 g/h needs about 180 g, roughly seven gels of 25 g plus some carbohydrate from drinks. At 30 g/h the same runner needs about five.

What is the best strategy for using energy gels during a marathon?

There is no single plan that fits everyone, but three rules hold up in the sources above: start early (30 to 45 minutes in), take gels with water at aid stations, and use only products you have tested on long runs. Then set the interval by time, not by a distance copied from someone running at a different pace.

How does a marathon fueling calculator work?

It multiplies your expected race time by a target carbohydrate rate, then spreads that total across the race as intakes. The quality of the output depends on the finish-time estimate and on whether the rate matches what your gut has handled in training.