EST Endurance Hydration & Fuel · ACSM & Jeukendrup

Sweat Rate, Sodium & Intra-Session Fuel Calculator

Compute your hourly sweat loss from pre- and post-session body weight (kilograms lost times 1,000, plus the millilitres you drank), check it against the ACSM 2% body-mass threshold and a roughly 1,000 mL/hr gut limit, and get a starting range for sodium (mg/L) and carbohydrate (30-90 g/hr).

Core Equation & Guard-Rail

Sweat Rate (mL/h) = ((Pre kg − Post kg) × 1000 + Drank mL) ÷ Hours · Post-Session = 1.5 L per kg lost

Drink to replace most of your sweat, not more: drinking beyond what you lose can dilute blood sodium, so let thirst guide you too. The gut tolerates roughly 800 to 1,000 mL per hour during running, so if you sweat faster than that, start well hydrated and replace about 150% of the remaining deficit over 2 to 4 hours afterwards. Sodium and carbohydrate ranges are starting points, not prescriptions, and this is not medical advice.

Methodology, Guides & Coaching

Science: Hydration, Carbohydrate & Protein Science → Endurance & Triathlon Coaching → Hydration for Endurance Athletes Fuelling During Long Sessions What to Eat Before a Long Run Endurance & Marathon Coach HYROX Race Preparation AFL Match Hydration Swimming S&C Hub

EST Sweat Rate & Fuel Calculator

2 Peer-Reviewed Sources

Pre-Session (kg) Post-Session (kg) Duration (Min) Drank (mL) Sweat Saltiness

Sweat Rate [EST]

1.7 L/hr

1.6% body mass deficit

In-Session Drink

1000 mL/hr

Capped at gastric limit

Sodium Target

500 to 700 mg/L

Post: 1.8 L over 2-4h

Hourly Carbs

30 to 60 g/hr (Single-source glucose/maltodextrin)

Jeukendrup (2014)

A general fitness estimate, not medical advice. Fluid, sodium and carbohydrate ranges are starting points, so drink to thirst too, and speak to a doctor if you have a heart, kidney or blood pressure condition.

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About these numbers: Formula, guard-rails & 2 peer-reviewed citations ▾

Sweat Rate (mL/h) = ((Pre kg − Post kg) × 1000 + Drank mL) ÷ Hours · Post-Session = 1.5 L per kg lost

• Estimating sweat rate from body weight before and after exercise, the two per cent body-mass dehydration threshold, and replacing about 150 per cent of the fluid lost after exercise come from the ACSM position stand on fluid replacement. [Source]
• Hourly carbohydrate targets during endurance work scale with session duration rather than body weight: about 60 grams an hour for 2 to 3 hours, and up to about 90 grams an hour of multiple-transportable carbohydrates in ultra-endurance events, for well-trained athletes. [Source]

Read Hydration, Carbohydrate & Protein Science → Hydration for Endurance Athletes Fuelling During Long Sessions What to Eat Before a Long Run Endurance & Marathon Coach HYROX Race Preparation AFL Match Hydration Swimming S&C Hub

General fitness and training estimates only, labelled EST. Not medical advice or a clinical diagnosis.

Verified Literature

Peer-reviewed sources behind this calculator

Read full methodology in the Science Hub →

Estimating sweat rate from body weight before and after exercise, the two per cent body-mass dehydration threshold, and replacing about 150 per cent of the fluid lost after exercise come from the ACSM position stand on fluid replacement.

American College of Sports Medicine; Sawka, M.N., Burke, L.M., Eichner, E.R., Maughan, R.J., Montain, S.J. & Stachenfeld, N.S. "American College of Sports Medicine position stand. Exercise and fluid replacement." Medicine & Science in Sports & Exercise, 2007;39(2):377-390. doi:10.1249/mss.0b013e31802ca597

View the source

Hourly carbohydrate targets during endurance work scale with session duration rather than body weight: about 60 grams an hour for 2 to 3 hours, and up to about 90 grams an hour of multiple-transportable carbohydrates in ultra-endurance events, for well-trained athletes.

Jeukendrup, A. "A step towards personalized sports nutrition: carbohydrate intake during exercise." Sports Medicine, 2014;44(Suppl 1):S25-S33. doi:10.1007/s40279-014-0148-z

View the source

Deep-Dive Training Guides

Automatic Tracking & Adaptation

Let Pelaris compute and track this automatically

Inside Pelaris, you never need to punch numbers into a spreadsheet. Every logged set, run and check-in updates your estimates automatically and adapts next week’s sessions.

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Frequently asked questions: Sweat Rate & Fuel Calculator

How do I perform a 1-hour sweat-rate test?

Weigh yourself nude or in dry minimal kit immediately before a 60-minute session, track the exact millilitres of fluid you drink during the workout, towel off and weigh yourself immediately after. Each 1 kg lost equals 1,000 mL of sweat.

Why do I need 1.5 litres of fluid for every 1 kg lost after training?

Sawka et al. (ACSM Position Stand, 2007) established that obligatory urine production continues during recovery, so drinking 150% of your net body-mass deficit over 2-4 hours with sodium is required to restore full hydration.

When should I switch to 60-90g/hr dual-source carbohydrates?

Jeukendrup (2014) explains that intestinal glucose absorption via SGLT1 saturates near 60 grams per hour, and that combining glucose or maltodextrin with fructose (GLUT5 transporter) lets well-trained athletes take in up to about 90 g/hr in very long events. Practise it in training before race day.