Sodium Calculator
Your race sodium target is 65 to 85% of what you lose in sweat, not 100%. An average sweater running a 3.5-hour marathon in mild weather loses roughly 560 mg of sodium per hour and should replace about 370 mg per hour, alongside 20 oz of fluid. Salty sweaters in heat can need triple that.
Enter your event, weight, sweat profile, and climate to get a per-hour sodium and fluid plan, a pre-race loading card, and an hour-by-hour breakdown. We call the output your Race Sodium Plan.
EB says
920 mg
Sodium
Per ACSM Position Stand: Exercise and Fluid Replacement (Medicine and Science in Sports and Exercise (Sawka et al., 2007))
Enter your sweat and race details to see your sodium plan.
Gear up
Sodium sources athletes actually buy
Salty sweaters: standard sports drinks will not keep up. Test any new sodium strategy in training first.
- Endurance360 CompleteHigh-sodium electrolyte built for salty sweaters and long races. Replaces what standard sports drinks miss.Shop Endurance360 →
- High-dose salt capsules (500-600 mg)The most reliable per-dose sodium for salty and very-salty profiles.View on Amazon →
- Salt tablets (300 mg)Easy to split across the hours. Pair each with 6 to 8 oz water.View on Amazon →
- High-sodium electrolyte drink mix1000 mg/serving formulas for athletes who lose a lot.View on Amazon →
As an Amazon Associate we earn from qualifying purchases.
Want to make the mix?
Homemade Electrolyte Drink Calculator
Turn this sodium target into an exact DIY recipe with potassium and magnesium.
Fueling too?
DIY Sports Drink Calculator
Add carbs to your bottle with a matched maltodextrin and fructose recipe.
Comparing store-bought?
Best Electrolyte Drink: DIY vs LMNT and Gatorade
How DIY stacks up against LMNT, Liquid IV, Nuun, and Gatorade on sodium, sugar, and cost.
How much sodium do you lose per hour?
Sweat sodium concentration averages 900 mg per liter but ranges from 400 to 1,800 mg/L between athletes. At a 1 liter per hour sweat rate, an average sweater loses 900 mg of sodium per hour. A heavy salty sweater at 1.5 L/h can lose over 2,700 mg/h.
Losses are the product of two variables: how much you sweat (rate) and how salty your sweat is (concentration). Both vary widely between individuals and conditions.
| Sweat rate | Low salt (400 mg/L) | Average (900 mg/L) | Salty (1,500 mg/L) |
|---|---|---|---|
| 0.5 L/h | 200 mg/h | 450 mg/h | 750 mg/h |
| 0.75 L/h | 300 mg/h | 675 mg/h | 1125 mg/h |
| 1.0 L/h | 400 mg/h | 900 mg/h | 1500 mg/h |
| 1.25 L/h | 500 mg/h | 1125 mg/h | 1875 mg/h |
| 1.5 L/h | 600 mg/h | 1350 mg/h | 2250 mg/h |
| 2.0 L/h | 800 mg/h | 1800 mg/h | 3000 mg/h |
How much sodium should you replace per hour?
Replace 65 to 85 percent of sweat sodium losses, not 100 percent. Full replacement is unnecessary because sodium is stored in interstitial fluid and bone, and attempting 100 percent replacement in heat often means consuming more fluid than you can absorb, increasing hyponatremia risk.
For an average sweater at 1 L/h (900 mg/h loss), the target is 585 to 765 mg/h. A SaltStick capsule delivers 215 mg. A Precision Hydration 1000 tablet delivers 1,000 mg per 500 mL. Matching your specific loss rate matters more than hitting a generic number.
- Training vs racing: During training, replacing 50 to 65 percent is fine. The gut adapts. Reserve high-sodium strategies for race day when you cannot afford GI problems.
- Events over 3 hours: Sodium depletion compounds. A 400 mg deficit per hour becomes a 1,600 mg deficit by hour 4. Front-load slightly in the first half of long events.
- Hot conditions: Sweat rate and concentration both rise with temperature. A plan that works at 60F will under-deliver at 85F. Re-run the calculator for race-day conditions.
Signs of sodium depletion during a race
Sodium depletion looks like nausea, muscle cramping, brain fog, and bloating that gets worse as you drink more plain water. Unlike simple dehydration, drinking plain water makes sodium depletion worse because it further dilutes blood sodium.
| Symptom | Likely cause | What to do |
|---|---|---|
| Nausea worsens after drinking | Sodium depletion / early hyponatremia | Stop plain water. Take a sodium capsule. Small sips of salty fluid. |
| Muscle cramps in legs or abdomen | Neuromuscular fatigue or electrolyte imbalance | Salt capsule or pickle juice shot (100-200 mg sodium). |
| Puffy hands or fingers | Water retention from low blood sodium | Stop plain water. Sodium source immediately. |
| Headache and confusion | Possible hyponatremia (seek medical attention if severe) | Stop and notify race medical staff if confusion is present. |
| Extreme thirst despite drinking | Cells dehydrated from sodium-water imbalance | Switch to a sodium-containing drink, not plain water. |
Severe symptoms (confusion, seizure, inability to walk) are a medical emergency. Notify race officials immediately.
How much sodium do you need per hour?
Most endurance athletes lose 500 to 1,500 mg of sodium per liter of sweat and sweat 0.5 to 2 liters per hour, so hourly sodium loss runs from roughly 300 to over 1,500 mg. The evidence-based replacement target is 65 to 85 percent of what you lose, not 100 percent. An average sweater in mild conditions needs around 300 to 500 mg per hour; a salty sweater in the heat can need 1,000 mg or more.
| Sweat profile | Sodium in sweat | Loss at ~1 L/hr | Replace (65-85%) |
|---|---|---|---|
| Light / low-sodium | ~500 mg/L | ~500 mg/hr | 325 - 425 mg/hr |
| Average | ~900 mg/L | ~900 mg/hr | 585 - 765 mg/hr |
| Salty sweater | ~1,500 mg/L | ~1,500 mg/hr | 975 - 1,275 mg/hr |
Multiply by your real sweat rate: at 2 L/hr the hourly loss roughly doubles. Enter your weight, sweat profile, and race climate above for a personalized target.
Sodium calculator FAQ
How much sodium do I need per hour during a race?
Most endurance athletes lose 500 to 1,500 mg of sodium per liter of sweat and sweat 0.5 to 2 liters per hour, so hourly sodium loss ranges from roughly 300 to over 1,500 mg. The evidence-based replacement target is 65 to 85% of that loss, not 100%. This calculator estimates your specific number from your weight, sweat profile, and the race climate. An average sweater in mild conditions typically needs around 300 to 500 mg per hour.
How do I know if I am a salty sweater?
The most reliable field sign is white residue on your skin, face, or dark clothing after a hard effort. Light streaks suggest an average profile, a visible gritty crust suggests salty, and a heavy salt rime with a salty taste on the skin suggests very salty. Frequent muscle cramping late in long events is another marker. A sweat test in a lab gives an exact number, but the visual self-test is accurate enough to pick a profile here.
Can you have too much sodium during exercise?
Sodium itself is rarely the problem; the bigger risk at the low end is hyponatremia, which is diluted blood sodium from drinking too much plain water relative to how much you sweat. Light sweaters in long, cool events are most at risk. The fix is to drink to thirst, not on a fixed schedule, and to make sure every drink contains sodium once you pass two hours. This tool flags your hyponatremia risk tier directly.
Should I load sodium before a race?
Pre-race sodium loading in the 24 hours before a hot or long event can expand blood plasma volume and delay dehydration. A practical target is an extra 500 to 1,500 mg in the day before, scaled to how salty you sweat and how hot the race is. The simplest tools are salting your meals, a salty snack at dinner, and an electrolyte capsule with breakfast. The pre-race card in your result lays out the exact food plan.
How do I measure my real sweat rate?
Weigh yourself nude before a one-hour run or ride, towel off and weigh again after, and track any fluid you drank. Each kilogram of body-weight loss equals about 1 liter (1,000 mL) of sweat. Add back what you drank. For example, losing 0.8 kg while drinking 500 mL means a sweat rate of about 1,300 mL per hour. Enter that number in the advanced field and the calculator uses it directly instead of estimating from body weight.
How much sodium do you lose sweating? (with data by sport) →
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