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FREE SPORTS SCIENCE TOOL · ACSM · NATA · EAH CONSENSUS · SWEAT RATE TESTED

Sports Hydration
Calculator.

Evidence-based fluid and sodium targets using your measured sweat rate, event duration, and climate conditions. Built on ACSM Position Stand and Third International EAH Consensus guardrails.

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Free · No sign-up · Estimates for planning, not a clinical prescription

ACSM Position Stand 2007
EAH Consensus · NATA · AIS
Pre/Post Sweat Rate Formula
Sodium 300–800 mg/hr · EAH Guardrails

Enter Sweat Test & Event Details

Pre/Post body mass test · Climate · Event · Sodium phenotype

No lab data? Use our default estimates. You can still get an accurate personalised hydration plan. For precision, complete a 45–90 min sweat test on a representative training session.
Sweat Test: Body Mass * Weigh nude (or with consistent dry clothing) before and after a training session. Towel-dry skin post-exercise. Do not use toilet before post-weigh.
Fluids During Test Session * Total volume consumed during the test, not before. 1 standard water bottle = 500 mL = 0.50 L. Enter 0 if you drank nothing.
📌 Enter 0 if you did not urinate during the test session (most common)
Test Session Duration * Duration of the exercise bout between the two weighings. 45–90 minutes is ideal. Shorter sessions have less precision.
🏟️ Event & Performance Details
Sport / Activity Type * Affects sweat rate estimate, fluid access frequency, and sodium defaults. Team sports have intermittent access; endurance events have more structured aid station intervals.
Planned Event Duration * Determines the replacement fraction (f) applied to sweat rate. Longer events require higher replacement to stay within 2% mass loss. Fluid needs are cumulative, totals displayed alongside per-hour targets.
Exercise Intensity * Higher intensity increases sweat rate by 10–20%. If test conditions matched race intensity, select "Same as test". Race pace is typically higher than training pace.
🌡️ Climate & Environment
Event Temperature * Air temperature at the event. Each +5°C above test conditions increases sweat rate ~10–15%. Indian summer competition heat (>35°C) is a severe sweat rate amplifier.
Humidity Level * High humidity impairs evaporative cooling → higher sweat rate. Indian monsoon conditions (high temp + high humidity) are among the most challenging scenarios for athletes.
Clothing & Equipment Burden * Heavy protective gear (football pads, rugby kit) impairs sweat evaporation and increases heat load, raising sweat rate by 10–20% vs shorts and t-shirt.
🧂 Sodium & Electrolyte Profile
Sodium / Sweat Phenotype * Sweat [Na+] varies from 10–90 mmol/L between athletes. Salty sweaters (white crust on skin/kit, stinging sweat) lose far more sodium per litre than average. Lab sweat sodium testing gives the most accurate value.
📌 If you have a lab sweat sodium result, enter it here (typical range 10–90 mmol/L). This overrides the phenotype selection above.
Medical / Risk History * Select all that apply. These activate additional safety guardrails in the calculator output. Overdrinking is the primary cause of exercise-associated hyponatremia (EAH).

ACSM 2007 · NATA · EAH Consensus · Sawka et al. · Shirreffs & Sawka · AIS Supplement Framework

FLUID TARGET (ACSM/EAH CALIBRATED)
Complete the form →
SWEAT RATE
— L/h
Adjusted
Na TARGET
— mg/h
Sodium/hour

About this tool

Sweat rate varies enormously between athletes, from about 0.3 to over 2 L per hour, and up to 5.7 L/h in extreme cases (Baker 2016), so generic "drink 8 glasses" advice is useless for training and racing. This calculator turns a measured sweat-rate trial (or a sport-based estimate) into an ml/hour fluid target, an mg/hour sodium target adjusted for your sweat-sodium phenotype, and an aid-station interval plan, with guardrails from the ACSM Position Stand and the Third International EAH Consensus Statement. Weigh in before and after your event to validate the plan.

WHAT YOU GET

ml/hour Fluid TargetACSM-calibrated range with safety guardrails
Sodium mg/hourPhenotype-adjusted · 300–800 mg/hr range
Body Mass Change Prediction0–2% loss target · EAH gain warning
Race Interval Planml per 15/20/30 min aid station
Climate AdjustmentTemperature × humidity × clothing multipliers
EAH Safety GuardrailsEAH Consensus + ACSM Position Stand

WANT MORE?

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Hydration Strategy

Our sports dietitian will create a personalised event hydration plan with product recommendations, electrolyte schedule, and pre-race loading protocol.

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EVIDENCE BASE

Sawka et al. (2007)ACSM Position Stand: Exercise and Fluid Replacement
EAH Consensus (2015)3rd International Consensus Statement
NATA (2000)Fluid Replacement for Athletes guidelines
Bennett et al. (2020)Wilderness Med Society: EAH clinical guidelines
AISSports Supplement Framework · Sodium

TRY ALSO

VO₂max + Calorie CalculatorCooper test · ACSM fitness norms
Hypertension Risk (ESH/ESC)BP risk + DASH sodium target
Smart Health CalculatorBMI · TDEE · NIN food groups

Frequently Asked Questions: Sports Hydration

How much water should I drink per hour during exercise?

There is no single number. It depends on your sweat rate, which typically ranges from about 0.3 to over 2 L per hour and can reach 5.7 L/h in extreme cases (Baker 2016). The ACSM Position Stand recommends drinking enough to limit body-mass loss to under about 2%, without gaining weight. This calculator converts your measured or estimated sweat rate into an ml/hour range adjusted for climate, intensity and duration, rather than applying a generic figure.

How do I measure my sweat rate?

Weigh yourself (minimal dry clothing, towelled off) immediately before and after about 60 minutes of exercise in conditions similar to your event:

Sweat rate (L/h) = [(pre-exercise mass − post-exercise mass) + fluid drunk − urine passed] ÷ test duration in hours

1 kg of mass lost is treated as roughly 1 L of fluid. Repeat the trial in hot and cool conditions, because sweat rate is condition-specific.

How much sodium do I need per hour when exercising?

The ACSM guidance is expressed as a sodium concentration of roughly 0.5–0.7 g per litre of fluid consumed during prolonged exercise; this tool derives an hourly figure from that plus your sweat rate and sodium phenotype, bounded to a practical 300–800 mg/hour display range. Sweat sodium concentration varies widely between athletes, so salty sweaters (visible salt crusting, salty-tasting sweat) sit at the higher end. Sessions under about an hour in cool conditions generally need no added sodium.

What is exercise-associated hyponatremia (EAH)?

EAH is a dilution of blood sodium below 135 mmol/L that occurs during or within 24 hours of prolonged exercise, most often caused by drinking more fluid than you lose. It can be fatal. The strongest single risk factor is gaining body mass during exercise, so you should never drink to the point of weight gain. Symptoms include headache, nausea, bloating, confusion and in severe cases seizures. These require immediate medical attention, not more plain water.

Should I drink to thirst or follow a fixed hydration schedule?

The Third International EAH Consensus Statement recommends drinking to thirst as a safe default, particularly in mass-participation events, because it protects against over-drinking. A planned schedule is more useful for high-sweat-rate athletes in hot conditions or where drinking opportunities are limited by aid-station spacing. A practical approach is to use the calculated ml/hour as an upper guide while still respecting thirst, and to validate it by weighing before and after.

How much should I drink before exercise?

The ACSM Position Stand suggests roughly 5–7 ml per kg of body mass at least 4 hours before exercise, which for a 70 kg athlete is about 350–490 ml. If urine is dark or scanty, a further 3–5 ml/kg can be taken about 2 hours before. The aim is to start the session euhydrated with pale-yellow urine, not to hyperhydrate, which raises the risk of exercise-associated hyponatremia without improving performance.

⚕️ This tool provides evidence-based hydration estimates, not clinical prescriptions. Individual sweat rates and sodium losses vary widely. For athletes with history of EAH, heat illness, or cardiac/renal conditions, consult a sports physician or accredited sports dietitian before implementing any hydration plan. The EAH Consensus Statement recommends "drink to thirst" as a safe default in mass-participation events. Never drink to the point of weight gain during exercise. Pre/post body mass monitoring is the gold standard for validating any hydration strategy on event day.