How many gels do I need for a marathon?

Most marathon runners need 5-8 gels depending on pace and carb targets. Faster runners (sub-3:30) may need fewer as they are running for less time.

How often should I take a gel?

Typically every 30-45 minutes. The key is consistent intake rather than large amounts at once, which can cause stomach distress.

No. Gels range from 20-30 g of carbs. Check the label of your preferred brand and enter the value in this calculator for accurate results.

Yes, most gels are designed to be taken with water to aid absorption. Isotonic gels can be taken without water but still benefit from fluid intake.

Calculate how many energy gels you need and when to take them.

Race Distance

Pace (min)

Pace (sec)

Carbs per Gel

Carb Target per Hour

The number of gels is based on your target carbohydrate intake per hour and total race duration:

Gels Needed = (Carbs/hr x Race Duration) / Carbs per Gel

Current sports science recommends 30-60 g/hr for events up to 2.5 hours, and 60-90 g/hr for longer races using multiple transportable carbohydrates.

Calculate calories burned during a run based on weight and pace.

Calculate how much fluid you need before, during and after running.

Calculate carbohydrate intake for race-week carb loading.

Plan your race-day fuelling strategy with gels, drinks and snacks.

Calculate electrolyte replacement needs based on sweat rate.

Last updated: February 2026

All calculations are estimates. Always consult a coach or medical professional for personalised training advice.