Hydration

Sweat Rate Calculator

Calculate your personal sweat rate from pre/post-exercise weigh-ins and estimate fluid and sodium losses (ACSM and NATA guidance).

Result

Sweat rate

1.3 L/hr

Total fluid lost

1.3 L

Body weight lost

1.1%

Drink per hour

1.05 L/hr

Sodium per hour

1,196 mg

Sweat versus drinking

What you sweat each hour, what to drink each hour, and the session total.

Sweat rate, per hour

1.3 L/hr

Drink, per hour

1.05 L/hr

Total lost

1.3 L

Hydration status

Minimal dehydration

You lost 1.1% body weight. ACSM advises keeping losses under 2%. Aim for about 1050 mL/hr next time.

Education, not medical advice. The result comes only from the published formula and your inputs. How we check our formulas.

What does the Sweat Rate Calculator calculate, and which formula does it use?

Weigh yourself before and after a session: sweat rate (L/hr) = (pre-exercise weight − post-exercise weight + fluid drunk − urine) ÷ hours exercised, the ACSM/NATA weigh-in method. The calculator grades the body-mass loss with the NATA bands (under 1% well hydrated, 1-3% minimal, 3-5% significant, over 5% serious), suggests drinking about 80% of your sweat rate next time, and estimates sodium loss at about 920 mg per litre of sweat, a typical athlete average.

Last updated March 11, 2026.

Questions people usually ask

What is sweat rate?

Sweat rate is the volume of fluid lost through sweating per hour of exercise, measured in litres/hour. Average endurance athletes sweat 0.5–2.5 L/hr; heavy sweaters can exceed 3 L/hr in heat.

Which formula is used?

The ACSM (American College of Sports Medicine) standard formula: Sweat Rate (L/hr) = (Pre-weight − Post-weight + Fluid consumed − Urine produced) / Duration in hours. Each 1 kg body weight loss equals approximately 1 litre of sweat.

How do I weigh myself accurately?

Weigh yourself nude immediately before exercise, then nude again immediately after — before eating or drinking anything post-exercise. Use the same scale both times.

Do I need to track urine output?

For most workouts under 90 minutes, urine output is negligible and you can leave it at 0. For ultra-endurance events, tracking urine output improves accuracy.

Why does sodium loss matter?

Sweat contains sodium, about 920 mg per litre on average, so heavy sweaters lose a lot on long sessions; a drink with sodium and carbohydrate can sustain performance better than water alone (Sawka 2007). Hyponatremia itself comes mainly from drinking more than you lose, whether water or sports drinks (Hew-Butler 2017).

Is this tool free and private?

Yes. AI Fit Hub tools are free, browser-based, and no-signup. Your inputs stay in your browser.

Does this replace a sports dietitian?

No. These outputs are evidence-based estimates. For personalised hydration plans, especially for elite performance or medical conditions, consult a registered sports dietitian.

The formula, worked through

Formula Sweat Rate Formula
Sweat rate formula: (weight before − weight after + fluid drunk − urine) / hours. A worked 1-hour run, ACSM's 2% guidance and typical sweat sodium losses.

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Use it from an agent or code

Any agent can run this calculator by URL: put the inputs in the query string and get JSON back, with the inputs that used defaults and a line to cite (add format=md for markdown). MCP clients reach it through https://aifithub.io/mcp.

https://aifithub.io/api/run/sweat-rate-calculator?pre_weight_kg=70&post_weight_kg=69.2&duration_minutes=60&fluid_consumed_ml=500&urine_produced_ml=0

In code, import the same module; it runs where you import it, with no request or key.

import { compute } from "https://aifithub.io/engines/sweat-rate-calculator.js";

Input and output contract, TypeScript types and the guide for agents.