Energy and fueling arithmetic
Estimate the calories a race burns from your weight, distance, walking and climb. Then turn an hourly carbohydrate target into gels, drink and real food, and see the gap to expect.
Examples set distance, time, walking, climb and sleep. They keep your weight and fuel plan. Replace them with your own race and goal.
These set the calories burned.
Choose a carbohydrate tier, then match it to the products you use.
Printable fueling sheet
70 kg · 10% walked · 0 m climb · 50 g carbohydrate and 250 kcal an hour
About 517 kcal an hour on average
67 kcal per km
Spent across every hour, stops and sleep included
1,200 g carbohydrate over 24 fueling hours
Intake covers 48% of the burn
0.9 an hour at 22 g, after 30 g from drink
| Hour | Carbs | Energy in | Gels | Sports drink | Eaten so far | Burned so far | Gap |
|---|---|---|---|---|---|---|---|
| 0–1 h | 50 g | 250 kcal | 1 | 500 mL | 250 kcal | 517 kcal | 267 kcal |
| 1–2 h | 50 g | 250 kcal | 1 | 500 mL | 500 kcal | 1,034 kcal | 534 kcal |
| 2–3 h | 50 g | 250 kcal | 1 | 500 mL | 750 kcal | 1,551 kcal | 801 kcal |
| 3–4 h | 50 g | 250 kcal | 1 | 500 mL | 1,000 kcal | 2,067 kcal | 1,067 kcal |
| 4–5 h | 50 g | 250 kcal | 1 | 500 mL | 1,250 kcal | 2,584 kcal | 1,334 kcal |
| 5–6 h | 50 g | 250 kcal | 0 | 500 mL | 1,500 kcal | 3,101 kcal | 1,601 kcal |
| 6–7 h | 50 g | 250 kcal | 1 | 500 mL | 1,750 kcal | 3,618 kcal | 1,868 kcal |
| 7–8 h | 50 g | 250 kcal | 1 | 500 mL | 2,000 kcal | 4,135 kcal | 2,135 kcal |
| 8–9 h | 50 g | 250 kcal | 1 | 500 mL | 2,250 kcal | 4,652 kcal | 2,402 kcal |
| 9–10 h | 50 g | 250 kcal | 1 | 500 mL | 2,500 kcal | 5,168 kcal | 2,668 kcal |
| 10–11 h | 50 g | 250 kcal | 1 | 500 mL | 2,750 kcal | 5,685 kcal | 2,935 kcal |
| 11–12 h | 50 g | 250 kcal | 1 | 500 mL | 3,000 kcal | 6,202 kcal | 3,202 kcal |
| 12–13 h | 50 g | 250 kcal | 1 | 500 mL | 3,250 kcal | 6,719 kcal | 3,469 kcal |
| 13–14 h | 50 g | 250 kcal | 1 | 500 mL | 3,500 kcal | 7,236 kcal | 3,736 kcal |
| 14–15 h | 50 g | 250 kcal | 1 | 500 mL | 3,750 kcal | 7,753 kcal | 4,003 kcal |
| 15–16 h | 50 g | 250 kcal | 1 | 500 mL | 4,000 kcal | 8,269 kcal | 4,269 kcal |
| 16–17 h | 50 g | 250 kcal | 0 | 500 mL | 4,250 kcal | 8,786 kcal | 4,536 kcal |
| 17–18 h | 50 g | 250 kcal | 1 | 500 mL | 4,500 kcal | 9,303 kcal | 4,803 kcal |
| 18–19 h | 50 g | 250 kcal | 1 | 500 mL | 4,750 kcal | 9,820 kcal | 5,070 kcal |
| 19–20 h | 50 g | 250 kcal | 1 | 500 mL | 5,000 kcal | 10,337 kcal | 5,337 kcal |
| 20–21 h | 50 g | 250 kcal | 1 | 500 mL | 5,250 kcal | 10,854 kcal | 5,604 kcal |
| 21–22 h | 50 g | 250 kcal | 1 | 500 mL | 5,500 kcal | 11,370 kcal | 5,870 kcal |
| 22–23 h | 50 g | 250 kcal | 1 | 500 mL | 5,750 kcal | 11,887 kcal | 6,137 kcal |
| 23–24 h | 50 g | 250 kcal | 1 | 500 mL | 6,000 kcal | 12,404 kcal | 6,404 kcal |
| Food | Carbs per portion | Portions an hour to replace 20 g of gels |
|---|---|---|
| Medium banana | 27 g | 0.7 |
| Cooked white rice, 100 g | 28 g | 0.7 |
| Boiled potatoes, 100 g | 20 g | 1.0 |
| Salted pretzels, 30 g | 24 g | 0.8 |
| Half a jam sandwich | 20 g | 1.0 |
| Cola, 250 mL | 27 g | 0.7 |
Estimates from the ACSM running and walking equations. Heat, cold, technical terrain, a heavy pack and fatigue raise the real cost. Test every product and amount on long training days before race day.
The calculator uses the ACSM running and walking equations, converted at about 5 kcal per litre of oxygen:
The walking equation in ACSM's Guidelines for Exercise Testing and Prescription charges twice as much per metre of ascent as the running equation (1.8 versus 0.9 mL of oxygen per kg). The course may have a different mix of walking uphill and running on level ground, so the shared walking percentage is an approximation.
The ISSN ultramarathon position stand puts the cost of running at 47.8–71.7 kcal per km. That is the same as 1 kcal per kg for runners of about 48–72 kg. Heat, cold, technical terrain, a heavy pack and late-race fatigue all raise the real cost. The resting figure runs high for many people, especially asleep. Treat the result as a planning estimate, not a measurement.
In a study of a 24-hour race, runners spent about 13,100 kcal and ate about 4,800. A deficit of several thousand kilocalories is normal in any race over a few hours. The ISSN's broad range for ultras is 150–400 kcal an hour. The goal is steady intake that keeps your pace from fading, not a balanced budget. If you miss an hour, carry on with the plan. Doubling the next hour causes more trouble than the missed one did.
For road races, the ACSM joint position stand gives 30–60 g an hour for 1–2.5 hours and up to 90 g beyond that. The answer on what ultrarunners eat explains how the ranges differ. The 24-hour fueling plan and the backyard nutrition guide show how the rate changes through the night.
One trial gave 120 g per hour to 20 elite, gut-trained runners in a mountain marathon. That says nothing about a suitable rate for most runners or for a full day of racing; plan an intake you have practiced in comparable conditions.
Drink to thirst. The ISSN racing reference is 450–750 mL an hour, less on cool nights. For sodium it discusses 500–700 mg per litre of fluid. Count salty food and broth as well as drinks. Measure your losses with the sweat rate calculator before you rely on these numbers in heat; the hydration and sodium guide explains the warning signs.
This is arithmetic for healthy adults. If you have diabetes, a kidney, heart or digestive condition, or a history of hyponatremia, plan race intake with a clinician.
About 1 kcal per kilogram of body weight per kilometre, almost whatever the pace: roughly 70 kcal per km, or 113 per mile, for a 70 kg runner. Walking costs about half as much per km. Per 1,000 m of ascent, climbing adds about 4.5 kcal per kg running or 9 kcal per kg walking; the calculator uses your walking share for ascent too. Resting metabolism adds about 1 kcal per kg per hour.
About 3,250 kcal for a 70 kg runner finishing in four hours: roughly 2,950 kcal to cover the 42.2 km and about 300 kcal of resting metabolism. A 55 kg runner on the same schedule burns about 2,550 kcal.
Our 24-hour example, a 70 kg runner covering 160 km and walking 10% of it, burns about 12,400 kcal. The 28-hour mountain 100-miler with 5,000 m of climbing and 30% walking burns about 13,700 kcal, assuming the same walking share uphill. Runners in a measured 24-hour race spent about 13,100 kcal.
At our 50 g an hour default and 22 g gels, a four-hour marathon needs about 9 gels if gels are your only carbohydrate, or 4 if you also drink 500 mL of a 6% sports drink each hour. The ACSM gives 30–60 g an hour for 1–2.5 hours and up to 90 g beyond that.
No. You cannot absorb that much on the move, and you do not need to. Runners in a 24-hour race study ate about a third of what they spent. Our default plan replaces about half the burn in a 24-hour race; the aim is steady intake that keeps you moving.
Watches estimate from heart rate, speed and their own models, and some show active calories without resting metabolism. Compare the watch's active calories with the Movement line here, and its total with Calories burned.