How much sodium per hour do you need during exercise?

The two numbers that decide your sodium loss

Sodium loss per hour comes down to simple multiplication:

sodium lost per hour = liters of sweat per hour × sodium per liter of sweat

Neither number is fixed. Sweat rate changes with pace, heat, humidity, clothing and fitness. Sweat sodium concentration differs from one athlete to the next, and it also moves around for the same athlete.

Baker’s 2017 review in Sports Medicine puts whole-body sweat sodium at roughly 10 to 70 mmol/L ^[1]. Researchers report sodium in millimoles (mmol). One mmol of sodium weighs 22.99 mg/mmol, which is how you get the milligram range above.

So picture two runners on the same course, sweating the same liter in an hour. One sits near the bottom of that range and loses about 230 mg/L worth of sodium. The other sits near the top and loses about 1,610 mg/L worth. Same run, same sweat volume, several times the sodium. That spread is why a generic “take X mg per hour” rule misses for most people.

What a large dataset shows

The biggest normative dataset we use is Barnes and colleagues (2019), who compiled sweat tests on 1,303 athletes collected by the Gatorade Sports Science Institute ^[2]. For endurance athletes, the mean sodium loss was 51.7 mmol/h with a standard deviation of 27.8 mmol/h. In milligrams, that mean is about 1,189 mg/h.

Read the standard deviation as a warning. It is large relative to the mean, which means plenty of athletes lose far less than average and plenty lose far more. The same paper found American football and endurance athletes had higher sodium losses per hour than soccer, basketball and baseball players ^[2].

A population mean is a starting point for planning. It is not your number.

What changes your sweat sodium

Baker’s review lists several things that shift sweat sodium concentration ^[1]:

• Sweat rate: When you sweat faster, your sweat glands reabsorb less sodium, so the sweat comes out saltier.
• Heat acclimation: After a stretch of training in the heat, sweat sodium tends to fall.
• Diet: A week or two of eating much more or much less sodium moves sweat sodium in the same direction.
• Where you measure: A patch on the forearm and a patch on the back can read quite differently, which is why single-site patch tests are estimates.

The practical upshot: your number in a cool March long run and your number in an August race may not match. Test in the conditions you care about.

Do you need to replace all of it?

Probably not, and nobody has published a percentage that fits everyone.

The American College of Sports Medicine (ACSM) position stand on fluid replacement says programs should be customized because sweat rates and sweat electrolytes vary so much, and that drinks with electrolytes and carbohydrate “can provide benefits over water alone under certain circumstances” ^[6]. After exercise, the same document says normal meals with enough sodium, plus water, will restore hydration if you have time ^[6].

For short sessions, the sodium you lose is usually small next to what a normal day of eating provides. The picture changes in long events, hot conditions, and for people who sweat heavily or have salty sweat. That is where a planned sodium intake earns its place.

Sodium does not make overdrinking safe

This matters more than any sodium target. The 2015 consensus statement on exercise-associated hyponatremia (low blood sodium during exercise) found that drinking too much fluid is the main cause, and it recommends letting thirst guide how much you drink ^[5]. The ACSM position stand agrees: fluid intake that exceeds sweat rate is the primary factor ^[6].

Sports drinks and electrolyte mixes contain less sodium than blood. Drink far more of them than you sweat and you can still dilute your blood sodium ^[5]. Salt in the bottle is not a license to keep drinking past thirst.

How to work out your own sodium per hour

1. Measure your sweat rate: Weigh yourself before and after a typical session, count what you drank, and use the sweat rate calculator. The method is in our sweat rate guide.
2. Estimate your sweat sodium: Without a lab test, use the published range. If you know you run salty, lean toward the upper part of it.
3. Plug both into the hydration calculator: It turns your sweat rate, session length and conditions into a sodium range per hour, based on the ranges cited on our methodology page.
4. Match it to a drink: The calculator ranks drinks by how close they get to your target. You can also browse the full drinks database sorted by sodium per liter.
5. Test it in training: Try the plan on long sessions before race day. Adjust based on how you feel and how your weight changes.

How much sodium is in common drinks?

Labels list sodium per serving, and serving sizes differ, so compare per liter. A few examples from our database:

• Gatorade Thirst Quencher: 457 mg per liter
• Nuun Sport: 634 mg per liter, mixed as directed
• LMNT: 2,114 mg per liter, mixed as directed
• Precision Fuel & Hydration PH 1500: 1,586 mg per liter, mixed as directed

Mixing directions change the answer. If you add a stick to a bigger bottle, the sodium per liter drops. Our guide to sodium in sports drinks has the full table. If you already know you lose a lot, see electrolytes for heavy sweaters.