Hydration Check Calculator

This tool reads your hydration from urine color, the most reliable real-time indicator, then adds how much extra water to drink for your activity level and the heat.

Urine color scale (1 to 8), and what each one is worth in millilitres:

• 1 Clear to 3 Light yellow: well hydrated, nothing to make up. Clear all day can mean slightly over-hydrated.
• 4 Yellow: mildly dehydrated. About 350 mL, a glass and a half, over the next couple of hours.
• 5 Dark yellow: behind. About 600 mL, spread out rather than downed.
• 6 to 7 Amber to dark amber: significantly to severely dehydrated. About 800 mL with electrolytes, and stop exercising.
• 8 Brown: not a hydration reading at all. Brown urine can mean rhabdomyolysis (muscle breakdown), a liver problem, or blood, and drinking more water does not treat any of those. Call a clinician.

Sip, do not gulp. The figures above are deliberately spread over two hours. Healthy kidneys clear roughly 800 to 1,000 mL an hour, and drinking faster than that dilutes blood sodium instead of rehydrating you. Exercise-associated hyponatremia has killed marathon runners who were drinking too much, not too little, so a dehydration calculator that told you to put two litres away inside an hour would be giving you the wrong risk.

One honest caveat about the colour method. B vitamins turn urine bright yellow whatever your hydration, beetroot and some laxatives turn it pink or red, and rifampin turns it orange. Diuretics and a lot of coffee pale it out while you are still behind on fluid. Read the colour first thing in the morning, before supplements, and it is a much better signal.

Extra water for activity and heat (added to your normal intake):

• Lightly active: +500 mL
• Moderately active: +750 mL
• Intense exercise: +1,000 mL
• Moderate heat (70–85°F): +250 mL
• Hot (above 85°F): +500 mL

Electrolyte consideration: For activity over 60 minutes at moderate-to-high intensity, water alone is not enough. Sodium (500–700 mg/hour), potassium, and magnesium are lost in sweat and should be replaced.

Reference: total daily fluid (Institute of Medicine):

• Men: about 3.7 liters (125 oz) per day, including all beverages and food moisture
• Women: about 2.7 liters (91 oz) per day
• Pregnant women: about +10 oz; breastfeeding: about +13 oz
• Roughly 20% of daily fluid comes from solid food

For a weight-based daily target in ounces, use the Water Intake Calculator linked below. This page is a quick status check, not a full intake plan.