Calculator
Carbs per hour calculator
How many grams of carbohydrate to eat per hour on a ride, run, or swim, from how long and how hard it is. It's the same math Fuelwright uses to plan every session, at its default settings.
60 g/hr
150 g over 2:30
- Energy burned
- 1,568 kcal
- Intensity (IF)
- 0.70 · TSS 122
- Share from carbs
- 64%
- Carbs burned
- 100 g/hr
- Worth replacing
- 57 g/hr
- Range for a ride
- 60–120 g/hr
- ↑ Replacing the burn would only take 57 g/hr, but for a ride of an hour or more Fuelwright doesn't go below 60 g/hr.
- ✓ At or under 60 g/hr, glucose-only fuel absorbs fine.
How many carbs per hour do you need?
Most guidance lands between 30 and 120 g of carbohydrate an hour, and where you fall depends on two things: how hard you're going and how long. The harder the effort, the more of your energy comes from carbohydrate rather than fat. The longer the session, the more of what you burn has to come from what you eat, because the glycogen you started with runs out.
The calculator works it out in four steps:
- Energy per hour. For a ride, from power: intensity × FTP gives average watts, watts × time gives work in kJ, and kJ ÷ (0.24 × 4.184) gives kcal — the reason kJ and kcal come out nearly equal. A run uses about 1 kcal per kg per km; a swim uses intensity against your own threshold.
- Carbohydrate's share. At an easy IF of 0.6 about half your energy comes from carbohydrate; at threshold it's around 90%.
- How much of the burn to replace. About 55% on a ride or swim and 35% on a run, rising for sessions over two hours, when your stores are running low.
- What your gut can take. The result is kept within each sport's range: 60–120 g/hr on the bike, 30–90 g/hr running or swimming.
Every formula, constant, and source is in the app, with a worked example — and every constant can be changed if you'd do the math differently.
Carbs per hour for cycling
Targets for a rider with a 250 W FTP, by ride length and intensity. A higher FTP burns more, so the targets go up with it.
| Ride | IF 0.60 | IF 0.70 | IF 0.80 | IF 0.85 |
|---|---|---|---|---|
| 1:30 | 60 g | 60 g | 75 g | 86 g |
| 2:00 | 60 g | 60 g | 75 g | 86 g |
| 3:00 | 60 g | 60 g | 81 g | 93 g |
| 4:00 | 60 g | 63 g | 86 g | 99 g |
| 5:00 | 60 g | 65 g | 88 g | 101 g |
Carbs per hour for running
Running jostles the gut, so runners absorb less of what they burn: the targets are lower than for a ride of the same length. Here for a 70 kg runner, by run length and intensity.
| Run | IF 0.65 | IF 0.75 | IF 0.85 |
|---|---|---|---|
| 1:00 | 30 g | 39 g | 51 g |
| 1:30 | 30 g | 39 g | 51 g |
| 2:00 | 30 g | 39 g | 51 g |
| 3:00 | 30 g | 42 g | 55 g |
Why glucose and fructose above 60 g/hr
Glucose crosses the gut through one transporter, SGLT1, which saturates at around 60 g an hour. Past that, extra glucose sits in your stomach instead of reaching your muscles — the cause of most mid-race gut trouble. Fructose is absorbed through a different transporter, GLUT5, so mixing the two, at roughly 1 part glucose to 0.8 parts fructose, lets you take in well over 60 g/hr. Most modern drink mixes and gels labelled "2:1" or "1:0.8" are built for this. Rates above about 90 g/hr also need weeks of practice to train the gut.
Do you need carbs for a workout under an hour?
No. You carry roughly 400–500 g of glycogen — 1,600–2,000 kcal — in your muscles and liver, which covers an hour of even hard work. Eating well before and after matters more than anything during.
What the calculator can't know
It assumes steady effort and a typical carbohydrate-burning curve. Fat-adapted athletes burn less carbohydrate at a given intensity, punchy interval sessions burn more than their average suggests, and heat, altitude, and fatigue all raise the cost. Use the number as a starting point, then adjust it to how your sessions actually go.
For the energy side on its own, see the cycling calories burned calculator.