Sweat Rate Calculator

Sweat rate (L/hr) = (pre-weight − post-weight + fluid intake) / duration.

Inputs

Result

Loading calculator…
—

General calculation reads

Amazon affiliate
How Not to Be Wrong
Jordan Ellenberg - math thinking
Shop on Amazon
The Joy of X
Steven Strogatz - accessible math
Shop on Amazon
Scientific calculator (Casio fx-991EX)
Shop on Amazon

As an Amazon Associate we may earn from qualifying purchases. This does not add cost for you.

How to use this calculator

  • Weigh yourself nude before exercise.
  • Log every mL of fluid consumed during.
  • Weigh again after exercise (towel off, nude).
  • Calculate; aim to replace 60-80% during, finish hydrating after.

About this calculator

Sweat rate measures fluid loss per hour: the foundation of hydration strategy. Typical recreational athletes lose 500-800 mL/hr; competitive athletes 1.0-1.5 L/hr; elite endurance athletes in heat 2.0-2.5 L/hr. Replace 60-80% during exercise (more isn't absorbed). Losing >2% of body weight as sweat impairs performance. To measure: weigh nude before and after a 60-90 min effort, log everything drunk and any urine.

Frequently asked

Why nude weight?+
Sweat-soaked clothes hold ~200-500g of water — would under-count sweat loss. Towel off, weigh nude.
How does heat affect this?+
Sweat rate doubles or triples in 90°F+ vs. 60°F. Re-test for hot conditions; don't assume your fall sweat rate applies in summer.
Should I weigh sodium too?+
If you're a heavy sweater (>1.5 L/hr) or doing 3+ hour events, yes — get a sweat sodium test. Most are 600-800 mg/L; salty sweaters 1200+.
Why "replace 60-80%"?+
Above ~1 L/hr of intake, gut absorption can't keep up — extra fluid sloshes and causes nausea. Match output but don't exceed gut capacity.
How does altitude affect sweat?+
Increases by 10-25% at 2,000m+ due to higher respiratory loss and altered thermoregulation. Plan accordingly.

Related calculators

Calories Burned by Activity (MET) Calculator
kcal = MET × weight (kg) × hours. Compendium MET values for 14 common activities.
Karvonen Heart Rate Zones Calculator
Target HR = ((max HR − resting HR) × intensity) + resting HR. The HRR (heart rate reserve) method.
Max Heart Rate by Age (4 formulas)
Compare Tanaka, Fox (220−age), Gulati (women), and Nes formulas for age-based max HR.
Rest Day / Recovery Calculator
Recommended rest days = base + intensity adjustment − sleep credit + age adjustment.
Training Load Acute:Chronic Ratio (ACWR)
AC:WR = 7-day training load / 28-day average. Sweet spot 0.8-1.3; >1.5 raises injury risk.
Cycling Calorie Burn by Power Calculator
kcal ≈ avg watts × hours × 3.6 — direct from work done (kJ ≈ kcal at 25% gross efficiency).

More tools you might like

Hand-picked tools that pair well with this one — same audience, same intent.

Karvonen Heart Rate Zones Calculator
Calc

Target HR = ((max HR − resting HR) × intensity) + resting HR. The HRR (heart rate reserve) method.

Max Heart Rate by Age (4 formulas)
Calc

Compare Tanaka, Fox (220−age), Gulati (women), and Nes formulas for age-based max HR.

Calories Burned by Activity (MET) Calculator
Calc

kcal = MET × weight (kg) × hours. Compendium MET values for 14 common activities.

Cycling Calorie Burn by Power Calculator
Calc

kcal ≈ avg watts × hours × 3.6 — direct from work done (kJ ≈ kcal at 25% gross efficiency).

Rest Day / Recovery Calculator
Calc

Recommended rest days = base + intensity adjustment − sleep credit + age adjustment.

Dog Walker Service Rate Sheet
Docs

A clean, printable rate sheet for a dog-walking service — per-walk pricing by duration, multi-walk package deals with automatic per-walk cost, add-ons, after-hours and holiday surcharges, plus cancellation and payment terms.