What you need

You only need a few things:

• bathroom scales
• your running bottle or bottles
• a towel
• somewhere to note your numbers

Optional but helpful:

• kitchen scales if you want to weigh bottles before and after
• a spreadsheet or notes app to track results in different conditions

How to measure your sweat rate step by step

Step 1: Weigh yourself before your run

Go to the toilet first if you can.

Then weigh yourself just before you head out.

For the most accurate result, do this with minimal clothing or no clothing at all. That way you are not adding the weight of sweaty kit afterwards.

Write down your starting weight.

Step 2: Do a normal training run

You do not need to make this complicated.

Just do a session that reflects the kind of running you want to plan for.

A steady run of around 60 minutes is ideal for most runners. Longer sessions can work too, but once you get very long, fuelling, glycogen use, and other variables start muddying the numbers a bit.

While you run, keep track of how much you drink.

The simplest way is to use one bottle and know how much was in it to begin with.

Step 3: Weigh yourself after the run

When you finish, towel yourself off and weigh yourself again in the same way as before.

Consistency matters here.

If you weighed yourself before the run in minimal kit, do the same afterwards.

Write down your finishing weight.

Step 4: Add up what you drank

Work out how much fluid you consumed during the run.

If your bottle started with 500ml and finished empty, you drank 500ml.

If you had two bottles, add them together.

If you prefer to weigh bottles, that works too. A 1 gram change is roughly equal to 1 ml of fluid.

Step 5: Account for any toilet stop

Ideally, do the test on a run where you do not need the toilet.

If you did stop for a wee during the session, include an estimate of urine loss as well. That makes the result more accurate.

Step 6: Calculate your sweat rate

The basic idea is:

Sweat loss = body weight lost + fluid consumed − urine passed

Then:

Sweat rate = sweat loss ÷ time in hours

So if you lost 1.0 kg, drank 500 ml, ran for 1 hour, and did not go to the toilet:

• sweat loss = 1.0 L + 0.5 L = 1.5 L
• sweat rate = 1.5 L/hr

That means you were losing fluid at roughly 1.5 litres per hour in those conditions.

Worked example

Here is a simple example.

Before run: 75.0 kg
After run: 74.2 kg
Fluid consumed: 600 ml
Run time: 60 minutes
Toilet stop: none

Step 1: Work out body weight lost

75.0 − 74.2 = 0.8 kg

Step 2: Add fluid consumed

0.8 + 0.6 = 1.4 L

Step 3: Divide by time

1.4 ÷ 1 = 1.4 L/hr

So the estimated sweat rate is:

1.4 litres per hour

That would put you firmly in heavy sweater territory for that session.

What is a normal sweat rate for runners?

There is a wide range.

As a rough guide:

• Under 0.75 L/hr = lighter sweater
• 0.75 to 1.25 L/hr = moderate sweater
• 1.25 to 1.75 L/hr = heavy sweater
• 1.75 L/hr and above = very heavy sweater

This is only a guide, not a label.

The important thing is not whether your number looks high or low. The important thing is understanding your number in your conditions.

A few important things to remember

1. Your sweat rate will change

Do not expect one test to cover every run you ever do.

Your sweat rate may be very different in:

• winter versus summer
• easy runs versus hard sessions
• road races versus trail races
• short runs versus long ultras

That is completely normal.

2. You do not need to replace every drop

This is a big one.

The goal is not to drink exactly the same amount as you sweat every hour.

For many runners, that is not realistic, and for some it can be uncomfortable or unnecessary.

The real value of sweat rate testing is that it helps you avoid being wildly off.

3. Repeat the test a few times

One test is useful.
Three or four tests in different conditions is much better.

That is when patterns start to appear.

For example, you might find:

• 0.9 L/hr on cool easy runs
• 1.3 L/hr on steady long runs
• 1.7 L/hr on hot race efforts

Now you are no longer guessing.

How to use this in real life

Once you know your sweat rate, you can start building a more realistic hydration plan.

For example, if you sweat at 1.4 L/hr, you know that a couple of small sips every now and again may not be enough on a long hot run.

You can also combine your sweat rate with your sodium loss estimate to get a much clearer picture of your hydration needs.

That is where this gets really useful for heavy sweaters.

Next step: estimate your sodium loss

Sweat rate tells you how much fluid you are losing.

Your sodium estimate helps you understand how much salt you may be losing in that fluid.

Put the two together and you are much closer to a hydration strategy that actually matches your body.

Read next: 👉How to Estimate Your Sodium Loss
Also useful: 👉Hydration Strategy for Sweaty Runners
Gear guide: 👉 Best Electrolytes for heavy Sweaters

Final thought

If you are a heavy sweater, measuring your sweat rate is one of the most useful things you can do.

It turns hydration from guesswork into something much more practical.

You do not need to be perfect.
You just need to be more informed than you were before.

That alone can make a big difference on long runs and race day.