How do I calculate my running pace?

Use the Pace Calculator to convert between pace, distance, and time. Enter your distance and time to get average pace, or enter target pace and distance to estimate finish time.

How can I predict my race time for a different distance?

The Race Time Predictor uses the Riegel formula to estimate equivalent performances from a recent race result, with standard race distances and optional custom targets.

What is Grade Adjusted Pace?

Grade Adjusted Pace converts pace on hills into an estimated flat-equivalent effort so you can compare hilly runs, trail races, and road efforts more fairly.

How do wind and heat calculators help race planning?

The wind and heat calculators estimate how weather can change pace and race time, helping runners set realistic targets for headwinds, tailwinds, humidity, and hot conditions.

Which calculator should I use for a course-specific race plan?

Use the Race Planning Calculator when you have a target time or GPX file and want split planning, terrain-adjusted pacing, fueling, hydration, and PDF export.

How many carbs per hour should I take in a marathon?

For most runners in a race lasting over 2.5 hours, 60-90 g of carbohydrate per hour is the evidence-based range, and reaching the top of it requires a glucose:fructose mix rather than a single carbohydrate source. For a faster marathon under 2.5 hours, 30-60 g/h is the band. The number this calculator gives you is the lower of what the race duration supports and what your stated fuelling experience suggests your gut can handle, because the physiological ceiling and your personal ceiling are different limits and the smaller one always wins. If you have never trained your gut above 60 g/h, race day is not where you find out.

How much should I drink during a race?

The ACSM guideline is 0.4-0.8 L per hour for marathon-length events, and where you sit inside that depends on your size, your speed and the conditions. This calculator shows two figures on purpose: what you are likely to sweat, and what you should drink. They are not the same number, and they are not supposed to be. Finishing a race 1-2% of body mass down is normal and costs you nothing. Drinking to keep your weight level is how runners end up hyponatremic, which is more dangerous than being mildly dehydrated. If you want one rule: drink to thirst, use these numbers as the sanity check on what thirst is telling you, and never exceed your sweat losses.

How do I measure my own sweat rate?

Weigh yourself naked, or in minimal dry clothing, immediately before a run. Run for a known time, ideally at race effort and in conditions like your race. Track every millilitre you drink. Towel off, weigh yourself again in the same state, and note anything you passed as urine. Sweat loss is the weight you lost, plus what you drank, minus what you passed - a kilogram lost is treated as a litre of sweat. Divide by the hours to get litres per hour. Repeat it in different conditions if you can, because your rate in a cool morning session tells you less about a hot race than you would think. The measure panel on this page does the arithmetic and scales the result into your race day conditions.

Why does the plan tell me to eat less before a short race?

The pre-race meal is there to top up liver glycogen, and how much you need scales with how long you will be running. The guideline range is 1-4 g of carbohydrate per kilogram of body mass in the final 1-4 hours. A 70 kg runner racing a 5K needs about 70 g, near the bottom of the range, because a 5K is over long before glycogen is limiting and a large meal is only something to carry. The same runner racing a marathon needs closer to 245 g, because the race will run them out. A plan that prescribed the same meal for both would be wrong for one of them.

What if my race is longer or hillier than a road marathon?

The distance picker includes trail and ultra distances, and the plan lengthens with them: more intakes, a bigger total carbohydrate load, and more fluid and sodium. Two things it deliberately does not model are terrain and elevation, which change your speed and therefore your heat production. The honest way to handle that is to enter the goal finishing time you actually expect on that course rather than a road equivalent - duration is what drives every number here. If you want a plan tied to a specific course profile, with aid stations and per-kilometre splits, use the race planning calculator, which reads a GPX file.

Running Tools

Race Fuelling & Hydration Calculator

One plan for carbohydrate and fluid, on the same clock. Enter your weight, your race and the conditions you expect, and get the pre-race meal, the hourly carbohydrate target, what you will sweat, what you should drink, and when to take each of them.

Your Race

Body Weight (kg)

Carbohydrate and sweat loss both scale with body mass, so this is the one number the plan cannot guess for you. Enter 30-200 kg.

Race Distance

Determines whether the race needs in-race fuelling at all, and how long you will be out there.

Goal Finishing Time

Hours

Minutes

Duration drives everything here — how much you can absorb, how much you will sweat, and how many intakes fit. Leave it blank to use a typical time for the distance.

Race Start Time

Puts the pre-race meal and every intake on a clock you can actually follow on the morning.

You & The Conditions

Fuelling Experience

How much carbohydrate your gut has been trained to handle. This can only lower the target — it never pushes you above what the race duration supports.

Temperature (°C)

Humidity

The temperature you expect during the race, not the overnight low.

Sweat Rate

Pick the category that sounds like you, or measure it properly below - a measured rate replaces the category entirely.

Enter Your Weight And Race Distance

Every figure here scales with body mass and race duration, so the plan waits for both rather than showing you somebody else's race.

⚠️ Important Safety Notice

This calculator produces a starting point, not a prescription. Individual sweat rates vary several-fold between runners in identical conditions, and gut tolerance for carbohydrate is trainable and personal. Rehearse the plan in training long before race day. Drink to your losses, never beyond them: exercise-associated hyponatremia comes from overdrinking, and in a Boston Marathon study 13% of finishers were hyponatremic, concentrated among runners taking over four hours who drank at every station. If you have a medical condition, take medication that affects fluid balance, or have a history of cramping or gastrointestinal problems in races, speak to a sports dietitian or physician before following any fuelling plan.

About Race Fuelling & Hydration

Two things limit a long race: the carbohydrate you can get into working muscle, and the fluid you can replace without overdoing it. They are usually calculated separately and then have to be executed together, on the same clock, by one runner with two hands. This calculator treats them as one plan for that reason.

Carbohydrate Targets: The evidence band is set by race duration, not by distance. Under 45 minutes needs nothing. From about 1 to 2.5 hours, 30-60 g/h is the range, because a single carbohydrate source oxidises at roughly 60 g/h no matter how much more you swallow. Beyond 2.5 hours, up to 90 g/h becomes possible, but only with multiple transportable carbohydrates - a glucose:fructose blend that uses a second intestinal transporter. Your own experience then caps that target, because a gut that has never handled 90 g/h will not start on race day.

Fluid Targets: The ACSM position stand puts 0.4-0.8 L/h as the working range for marathon-length events, higher for larger and faster runners in the heat, lower for smaller and slower runners in the cold. This calculator places you inside that band using body mass and speed - the two things that set how much heat you produce - then adjusts for temperature, humidity and your sweat rate. It also shows estimated sweat loss next to recommended intake, and never recommends more than you lose.

Sodium: Sodium replacement matters once a race runs long enough for the losses to accumulate, which is why nothing is prescribed for short races. It helps you retain the fluid you drink rather than passing it straight through, and heavy and salty sweaters need meaningfully more than the average. Sodium is not a cramp cure - the evidence there is weak - but it is a genuine part of hydration over several hours.

Measuring Your Own Sweat Rate: Categories are a fallback. A weigh-in takes one run: weigh yourself before and after, towelled dry and in minimal clothing, track what you drink and anything you pass, and divide the total loss by the hours. Do it in conditions like your race, or tell the calculator what the conditions were and it will scale the result. It is the single highest-value input on this page.

Frequently Asked Questions

Related Running Calculators

Race Planning Calculator Heat & Humidity Calculator Running Pace Calculator Race Time Predictor

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