Carbs Per Hour Calculator for Trail Running & Ultras

Free carbs per hour calculator for trail runners. Enter distance, climbing and time to get a g/h target, total carbs, calories and how many gels to carry.

How It Works

Enter distance, elevation gain and loss, and expected duration
Add your body weight and how trained your gut is
Read your carbs-per-hour target, total carbohydrate, energy cost and product equivalents

Energy Cost Model

kcal = weight_kg × (0.95 × distance_km + 0.0094 × gain_m + 0.0028 × loss_m)

1 kcal per kg per km approximates horizontal running cost
Climbing adds the mechanical work of raising body mass (9.81 J/kg/m) at about 25% muscular efficiency
Descending adds a smaller eccentric-braking term

Carbohydrate Targets

Duration	Carbs per hour
Under 1 hour	0-30 g (not required)
1 to 2.5 hours	30-60 g
2.5 to 5 hours	55-80 g
Over 5 hours	60-90 g

The upper end requires multiple transportable carbohydrates (glucose plus fructose) and a gut that has practised it. The calculator caps the ceiling at 60 g/h for an untrained gut, 75 g/h with some practice, and 90 g/h when well practised.

Product Equivalents

Energy gel: about 23 g carbohydrate
Energy bar: about 40 g carbohydrate
500 ml sports drink: about 30 g carbohydrate

Caffeine

1-3 mg per kilogram of body weight, taken 45-60 minutes before you want the effect. For a 70 kg runner that is 70-210 mg. In long races, saving it for the second half generally works better than front-loading.

Key Principles

You are meant to finish a long effort in a calorie deficit. Fat oxidation covers what you do not eat. Do not try to break even.
Gut failure at hour four is the single most common reason for a blown ultra, and it is a training problem, not a product problem.
Past six hours, add savoury and solid options — sweet gels alone stop going down for most runners.

FAQ

How do I calculate carbs per hour? Pick the band for your duration (none under 1 hour, 30-60 g/h to 2.5 hours, 55-80 g/h to 5 hours, 60-90 g/h beyond), cap it by gut training (60 g/h untrained, 75 average, 90 well practised), then multiply by hours for total carbs.

How many carbs per hour for a trail ultra? 60-90 g per hour beyond about two and a half hours, if your gut is trained for it.

How many calories does trail running burn? Roughly 1 kcal per kg per km, plus about 0.0094 kcal per kg per metre of ascent.

Is my data stored? No. The calculator runs entirely in your browser.