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Sweat Rate Calculator: Your Workout Hydration Plan (Water + Sodium per Hour)

March 21, 2026

Calculate your sweat rate in one session and turn it into a simple hourly plan for gym training (with a Muay Thai version too) — plus sodium math and evidence-based ranges.

Sweat Rate Calculator: Your Workout Hydration Plan (Water + Sodium per Hour)

Most hydration advice is useless because it is generic.

You do not need “drink more water.” You need one number:

your sweat rate (liters per hour).

Once you know it, you can build a plan that actually works for:

  • normal gym sessions
  • hot gyms and hard conditioning
  • and Muay Thai, where drinking strategy matters because big chugs can make you feel awful

This article is gym-first because that is where a lot of search traffic comes from, but the method works for both.

If you want the baseline rules first, start with Hydration Basics: What Actually Matters.

The 60-second idea

Your body weight drops during training mostly because you lose fluid through sweat and breathing.

So if you measure:

  • body weight before training
  • body weight after training
  • and how much you drank

…you can estimate how many liters per hour you are losing.

That is your sweat rate.

Sweat Rate Calculator

You need:

  • a scale
  • your bottle, so you know how much you drank
  • a note of session time

Step 1: weigh in before training

  • weigh yourself right before you start
  • best: minimal clothing, dry skin
  • write it down in kg

Step 2: track what you drink

  • note your total fluid during the session
  • example: 750 ml = 0.75 L

Step 3: weigh out after training

  • towel off first
  • do not weigh a wet shirt
  • weigh yourself again in kg

Step 4: calculate sweat loss

Use this:

Sweat loss (L) = (weight before − weight after) + fluids drank − urine

Notes:

  • 1 kg lost is roughly 1 liter
  • if you did not pee during the session, urine = 0

Step 5: convert it to liters per hour

Sweat rate (L/h) = sweat loss (L) ÷ duration (hours)

That gives you the number you actually need.

Example: gym session

  • weight before: 87.0 kg
  • weight after: 86.2 kg
  • fluids during session: 0.60 L
  • duration: 75 min = 1.25 h
  • urine: 0

Sweat loss = (87.0 − 86.2) + 0.60 = 0.8 + 0.60 = 1.40 L Sweat rate = 1.40 ÷ 1.25 = 1.12 L/h

So in those conditions you are losing about 1.1 liters per hour.

That is a high-sweat session, and now you can actually plan for it.

Turn sweat rate into a drinking plan

During training, the goal is usually not to replace 100 percent of losses immediately.

A practical starting point:

  • aim for about 60–80% of your sweat rate
  • keep it within what your stomach tolerates
  • do not consistently drink more than you lose

A lot of practical exercise-hydration guidance ends up landing people somewhere around 0.4–0.8 L/h during exercise, but your own testing gives you a more useful starting point than generic advice.

Using the example

If your sweat rate is 1.12 L/h:

  • 60–80% = 0.67–0.90 L/h
  • a practical target could be 0.75 L/h

Now the advice becomes usable.

If you want the simpler before/during/after version too, read How Much Water to Drink When Training (Before, During, After).

Gym plan: strength or hypertrophy sessions

In the gym, you want hydration that:

  • does not bloat you
  • does not interrupt your sets constantly
  • is easy to follow

Easy rule

150–250 ml every 15–20 minutes

That gives you about:

  • 0.45–1.0 L/h, depending on the pattern you use

Quick templates

45–60 minute workout

  • moderate sweat: 300–600 ml total
  • heavy sweat or hot gym: 500–800 ml total

75–90 minute workout

  • common target: 0.5–0.8 L/h
  • if your sweat rate is high, move toward the upper end only if your stomach tolerates it

Muay Thai version

Muay Thai tends to mean:

  • more continuous movement
  • more heat
  • more sweat
  • less room for sloppy hydration

The math is the same, but the execution changes.

Between-round rule

Instead of constant sipping:

  • take 100–200 ml in short repeats between rounds
  • avoid chugging large amounts at once

If your measured sweat rate is high, for example 1.2+ L/h in a hot room, that still does not mean you should slam a full bottle mid-session.

Small repeats beat big chugs.

If you train twice in one day, this becomes even more important. Read How to Recover Faster Between Two Training Sessions in One Day.

Sodium: when it matters

If you train longer than about 1 hour and sweat heavily, sodium matters more.

A practical sodium target often used in longer-exercise guidance is:

about 500–700 mg sodium per liter

Sodium math

If you drink 0.75 L/h and aim for 500–700 mg/L:

  • 0.75 × 500 = 375 mg sodium/hour
  • 0.75 × 700 = 525 mg sodium/hour

So a practical range is:

about 400–500 mg sodium per hour for long, sweaty sessions.

What that means in real life

  • sports drinks vary a lot
  • electrolyte tablets vary a lot
  • labels matter

Sodium is more worth thinking about when you have:

  • a long session
  • heavy sweat
  • a hot room
  • salty sweat marks on clothes or skin
  • headaches or cramps when you only drink water

For the bigger picture, also read Electrolytes for Workouts: When You Need Them (and When You Don’t).

The biggest mistake: drinking more than you lose

More water is not always better.

Simple safety rule:

Do not consistently drink more than your sweat loss.

If your test shows you lose about 1.0 L/h and you are drinking 1.5 L/h, that is a red flag.

Signs you may be overdoing it

  • sloshing stomach
  • nausea
  • swollen fingers
  • headache after very heavy drinking
  • frequent clear urination mid-session

The 3-line setup

  1. Measure your sweat rate (L/h)
  2. Drink about 60–80% of that to start
  3. If the session is long and sweaty, add sodium at about 500–700 mg/L

That is your plan.

If you want the full picture around hydration timing and electrolytes:

Sources

Track hydration with Water Tracker Back to Hydration
Back to Blog More Hydration