Sport-Specific Water Intake (Pre / During / Post + Electrolytes)

Calculate fluid intake for athletes by activity type, sweat rate, duration, and climate, including pre-, during-, and post-exercise volumes plus electrolyte replacement per ACSM guidelines.

Activity intensity
Climate
Estimated sweat loss
0.70 L
0.70 L/h × 1.00 h
PRE (4 h prior)
19 oz
561 mL · 5–10 mL/kg
DURING
24 oz
700 mL · ~24 oz/h
POST
33 oz
962 mL · 1.25–1.5 L/kg lost
Electrolyte add (session ≥ 60 min)
Sodium: 350 mg total during exercise (target 300–700 mg/L of fluid)
From sports drink, salt tablet, or salted snack. Skip the sodium and you risk dilutional hyponatremia.

Per ACSM Position Stand on Exercise and Fluid Replacement (Sawka MN et al., Med Sci Sports Exerc 2007;39:377; reaffirmed 2024) + GSSI Sports Science Exchange SSE 237 (2024). Sweat rates from Baker LB et al., Sports Med 2017;47:111 — vary 50% individual to individual; weigh pre/post for personal calibration.

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About this tool

Performance hydration is a three-phase problem distinct from baseline daily intake. Per the American College of Sports Medicine Position Stand on Exercise and Fluid Replacement (Sawka MN et al., Med Sci Sports Exerc 2007;39:377) and updated 2024 IAAF/World Athletics guidance: PRE-exercise (4 hours before): drink 5–10 mL/kg body weight (about 12–20 fl oz for a 70-kg adult) to ensure euhydration and pale urine. DURING exercise: replace sweat losses to keep weight loss under 2% (the threshold where performance decline begins). Sweat rate varies enormously — 0.4 L/h easy cycling cool weather to 2.5 L/h hot-weather running — typical adults lose ~0.5–1.5 L/h. POST-exercise: drink 1.25–1.5 L per kg of body weight lost. For workouts over 60–90 minutes, add electrolytes: sodium 300–700 mg/L per ACSM, supplemented from sports drinks or salt tabs. The 2024 GSSI Sports Science Exchange Vol 33 No 237 review notes hyponatremia (low sodium) from over-drinking pure water is a real risk in marathon runners and endurance athletes — sodium loss matters as much as volume loss.

How to use it

  • Enter your body weight and the activity type, duration, and climate.
  • Read pre-, during-, and post-exercise fluid targets in fl oz and mL.
  • See sodium replacement recommendation for long sessions.
  • Weigh yourself before and after long workouts — actual fluid lost = weight delta + intake.

Frequently asked questions

How is this different from a daily water calculator?
Daily-intake calculators target baseline body needs (~30–40 mL/kg). This calculator adds exercise-specific replacement based on sweat rate × duration × climate, plus electrolyte guidance for sessions > 60 min — which the baseline tool does not cover.
How do I measure sweat rate?
Weigh yourself nude before and after a 60-min workout (subtract any fluid drunk during). Each 1 lb lost ≈ 16 fl oz of sweat. Pros do this monthly across temperature ranges to dial in personal rates.
When do I need electrolytes?
Per ACSM 2007: sessions > 60–90 min OR shorter sessions in hot/humid conditions OR for "salty sweaters" (white residue on clothing). Target 300–700 mg sodium per liter consumed.
Is hyponatremia really a risk?
Yes — exercise-associated hyponatremia from over-drinking water is documented at marathons (Hew-Butler T et al., Clin J Sport Med 2015). Match intake to thirst + sodium for long events; do not force-drink.
Is data sent anywhere?
No. All math runs in your browser.

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