How to use it
- Type your Body weight and choose kg or lb under Weight unit.
- Type the Event duration in hours, minutes and seconds, for example 2:30:00.
- Read Carbohydrate per day before the event and the amounts in Loading amounts per day.
- For race day, read Carbohydrate per hour during the event and Total carbohydrate during the event.
How the carbohydrate amounts are calculated
Carbohydrate loading means eating more carbohydrate for the 36 to 48 hours before a long event. GSSI gives 10 to 12 g per kg of body mass a day for this, and attributes the figures to Thomas, Erdman and Burke (2016). The grams a day are the grams per kg multiplied by your body mass in kilograms.
During the event, GSSI gives an hourly band by duration: 30 to 60 g per hour for 1 to 2.5 hours, and up to 90 g per hour for longer exercise. The total for the event is that band multiplied by the duration in hours.
Grams a day = g per kg × body mass (kg)
Body mass (kg) = lb × 0.45359237
Total during the event (g) = g per hour × duration (hours)- Each gram figure is rounded to a whole gram.
- This result is an estimate and not medical or dietary advice. People with diabetes, kidney disease or other conditions should ask their doctor or a dietitian first.
What this calculator does not cover
- Loading for events of 90 minutes or less. GSSI says such intakes may not be necessary for them, and the calculator shows a note.
- How well your gut copes with carbohydrate during exercise. Practise the hourly intake in training before race day.
- Your food, fluid and salt outside the loading days and the event itself.
- Diabetes, kidney disease, pregnancy or any other condition. Ask your doctor or a dietitian before changing your diet.
The rule and its source
The 10 to 12 g per kg figure for 36 to 48 hours, the 90-minute condition, and the 30 to 60 g and up to 90 g per hour bands are the figures of the GSSI article. GSSI attributes the loading figures to Thomas, Erdman and Burke (2016), Nutrition and Athletic Performance.
For the higher hourly intakes, GSSI advises mixtures of glucose and fructose. The article gives this advice without a citation, so it is shown here as GSSI's advice.
Worked example: 70 kg and a 3:00:00 event
Loading: 10 g × 70 kg = 700 g and 12 g × 70 kg = 840 g a day, so 700 to 840 g per day for the 36 to 48 hours before the start.
Race day: 3 hours is longer than 2.5 hours, so the band is up to 90 g per hour. 90 g × 3 hours = 270 g in total.
The event lasts more than 90 minutes, so the short-event note does not appear.
| Result | 70 kg, 3:00:00 event |
|---|---|
| Carbohydrate per day before the event | 700 to 840 g per day |
| Carbohydrate per hour during the event | Up to 90 g per hour |
| Total carbohydrate during the event | Up to 270 g in total |
Frequently asked questions
Do I need carb loading for a race under 90 minutes?
Usually not. GSSI says that for events under 90 minutes such aggressive intakes may not be necessary, so the calculator shows a note for those durations.
What is carb loading?
It is eating more carbohydrate for the 36 to 48 hours before a long event, so that the muscles start with more glycogen. GSSI gives 10 to 12 g per kg of body mass a day for this.
Why is the hourly figure up to 90 g above 2.5 hours?
GSSI gives 30 to 60 g per hour for exercise of 1 to 2.5 hours, and up to 90 g per hour for exercise longer than 2.5 hours. It also notes that up to 120 g per hour has been proposed, but that more evidence is needed before the consensus is raised.
Why does GSSI mention glucose and fructose together?
GSSI says that mixtures of glucose and fructose are consumed to maximise intestinal carbohydrate absorption, and that they give more flexibility in the amount taken during an event. This is GSSI's advice, given without a citation.
Can I enter my weight in pounds?
Yes. Choose lb under Weight unit. The page converts your weight with 1 lb = 0.45359237 kg before it multiplies by the grams per kg.
Does the calculator keep what I type?
No. The calculation runs in your browser, and nothing you enter is stored or sent to us.
Sources
Figures and text last checked on Tuesday, November 10, 2026.