Free tool

Sweat & Sodium Loss Calculator

Put in how long you moved and how hard you sweated, and this gives you a rough idea of how much sodium left your body, and roughly how many electrolyte serves that is worth putting back.

Rawstone · a rough general estimate, not medical or performance advice

How long was the session?

Total time you were active and sweating, in minutes. A gym session is often 45 to 90 minutes.

60 min

How much did you sweat?

A rough feel is fine. Light means you were barely damp. Heavy means you were dripping and your shirt was soaked.

What were the conditions?

Hotter and more humid air makes you sweat more for the same effort, so it nudges the estimate up a little.

I am on keto or fasting. Cutting carbs or fasting lowers a hormone called insulin, and that tells your kidneys to let go of more sodium in your urine across the day, on top of what you sweat out.

Estimated sodium lost this session

1,000 mg

That is roughly half a serve of a 1000mg electrolyte like Rawstone.

Rounded to the nearest whole serve. One Rawstone serve carries 1000mg of sodium. This is a ballpark for the session only, not a target you have to hit.

Because you are on keto or fasting, many low-carb guides suggest topping up an extra 500 to 1000mg of sodium across the whole day on top of what you sweat out, while your body adjusts. That is roughly another half to one serve spread over the day, separate from the session number above.

How the number is worked out

These are general estimates built from published sweat research, not a measurement of your own body. Real sweat sodium varies a lot from person to person.

Sweat lost (litres) = your sweat rate for the level you picked, times how long you were active.
Sodium lost (mg) = sweat lost, times a typical sweat sodium level of about 1000mg per litre, times a small multiplier for the conditions (cooler 0.9, warm 1.0, hot 1.2).
Serves = sodium lost divided by 1000mg, rounded to the nearest half serve.
The keto and fasting line is a separate whole-day context note of about 500 to 1000mg, not part of the session sum.

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By Tom Bolger, Rawstone co-founder. Rawstone is built by two founders with around thirty years of food and beverage manufacturing between them, and both of us train in the gym. Tom helped formulate Rawstone and will send every production batch to an independent lab, with the test certificate posted here publicly from our very first batch.

This tool gives a rough general estimate of sweat and sodium loss for education only. It is not medical or performance advice, and it does not measure your own body. Rawstone is a food supplement, not a medicine, and is not intended to diagnose, treat, cure or prevent any disease. If you manage your sodium intake for any health reason, talk to your doctor before changing how much you take in.