Hydration Calculator
Your per-hour race-day fluid target is roughly 75 percent of your sweat rate, capped near 800 mL (27 oz) per hour to avoid overdrinking. A 70 kg athlete sweating 1,000 mL per hour in mild weather should drink about 750 mL per hour, on top of a daily baseline near 2,100 mL.
Enter your weight, sweat rate, session length, and temperature to get a daily fluid baseline, a per-hour drinking target, an overdrinking risk check, and a urine-color audit you can use before and after a session.
Enter your weight, duration, sweat rate, and temperature, then hit calculate. Your plan appears here and the URL updates so you can bookmark or share it.
Urine color hydration audit
On the standard 8-point urine color scale, levels 1 to 3 mean you are well hydrated, levels 4 to 6 mean a fluid deficit, and levels 7 to 8 mean severe dehydration. Aim for pale straw to light yellow (levels 1 to 3) before a hard session and recheck two to four hours after.
This is a fast field check, not a lab test. Vitamin B supplements, beets, and some medications can darken urine independently of hydration, so read it alongside thirst and body-weight change.
| Level | Shade | Status | What to do |
|---|---|---|---|
| 1 | Pale straw | Well hydrated. Maintain your normal intake. | |
| 2 | Light yellow | Hydrated. No action needed. | |
| 3 | Yellow | Hydrated. A good pre-race target. | |
| 4 | Darker yellow | Slightly low. Drink 300 to 500 mL over the next hour. | |
| 5 | Amber | Dehydrated. Drink and add electrolytes; recheck in an hour. | |
| 6 | Dark amber | Clearly dehydrated. Rehydrate before training or racing. | |
| 7 | Brown-yellow | Severe deficit. Rehydrate now; do not start a hard effort. | |
| 8 | Brown | Severe dehydration. Rehydrate and seek advice if it persists. |
How much water should you drink per day?
A practical daily fluid baseline for an active adult is 30 to 35 mL per kilogram of body weight, before exercise. That puts a 60 kg athlete near 1,800 to 2,100 mL and a 90 kg athlete near 2,700 to 3,150 mL. Training replacement is added on top, scaled to sweat rate.
| Body weight | Daily baseline (30 mL/kg) | In fluid ounces |
|---|---|---|
| 50 kg (110 lb) | 1,500 mL | 51 oz |
| 60 kg (132 lb) | 1,800 mL | 61 oz |
| 70 kg (154 lb) | 2,100 mL | 71 oz |
| 80 kg (176 lb) | 2,400 mL | 81 oz |
| 90 kg (198 lb) | 2,700 mL | 91 oz |
Hydration calculator FAQ
How much water should I drink per hour during exercise?
For most endurance athletes in temperate conditions, 400 to 800 mL per hour (13 to 27 fl oz) is the target range. In heat or at high sweat rates you may need up to 1,000 mL per hour. Drink to thirst as the primary guide and use this calculator to set a personalized ceiling so you never go far above your sweat rate.
How much water should I drink per day?
A practical daily baseline for an active adult is about 30 to 35 mL per kilogram of body weight, before exercise is added. A 70 kg (154 lb) athlete lands near 2,100 to 2,450 mL. Training adds replacement on top of this, scaled to sweat rate and how long and hot the session is.
Does drinking plain water cause hyponatremia?
Drinking large volumes of plain water without replacing sodium can dilute blood sodium and cause exercise-associated hyponatremia. The risk is highest in slower athletes exercising for more than four hours who drink beyond thirst. Including electrolytes in fluids over long efforts is protective, which is why this tool flags an overdrinking risk tier.
How do I read the urine color hydration chart?
On the standard 8-point Armstrong scale, levels 1 to 3 (pale straw to yellow) indicate good hydration, levels 4 to 6 (darker yellow to amber) indicate a fluid deficit, and levels 7 to 8 (brown-yellow to brown) indicate severe dehydration. Aim for pale straw to light yellow before a hard session, and recheck a few hours after.
How do I calculate my sweat rate?
Weigh yourself nude before and after a 60-minute workout without drinking. Every kilogram of body mass lost equals roughly 1 liter (1,000 mL) of sweat. Add any fluid you drank during the hour to get total sweat loss. Repeat in similar conditions to get a reliable average, then enter it here.
Need your sweat rate?
Sweat Rate Calculator
Measure your real per-hour sweat loss, then bring it back here.
Pair it with salt
Sodium Calculator
Fluid alone is not enough on long efforts. Match a sodium target to your sweat.
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.
See also: Signs of dehydration during exercise →
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