Water Intake Calculator — daily target + drink log

Real-world use cases

• A 78 kg office worker who keeps forgetting to drink

  You sit at a desk all day and only notice thirst by 4pm. Enter 78 kg, sedentary, temperate: the tool says 2.35 L total, about 1.9 L to actually drink. That's roughly 8 cups of 250 ml. Tap "+1 cup" each time you refill, and the progress bar tells you at lunch whether you're on pace or already two cups behind.

• Summer half-marathon training in a hot climate

  You're 70 kg and run 90 minutes most mornings before the heat builds. Set high activity and "hot" climate: the base 2.1 L jumps to about 3.3 L once the 900 ml exercise adder and the heat adder stack on. Weigh yourself before and after one long run, and replace every kilogram lost with roughly 1 L on top.

• Trying to lose weight by drinking before meals

  You want the appetite trick from the Dennis 2010 trial: 500 ml of water 20 to 30 minutes before each meal. The calculator gives a 75 kg person a 2.25 L daily target, and three pre-meal glasses already cover 1.5 L of it. Log those three first, then top up between meals so you hit the number without forcing it.

• Checking whether "8 cups a day" is enough for you

  The 8-cup rule is a round number for a 65 kg adult in mild weather. Enter your real weight and climate to see how far off it is. An 88 kg man in a warm office gets about 2.6 L total, 2.1 L to drink, which is closer to 9 cups than 8, so the old rule quietly leaves him a cup short every single day.

Common pitfalls

• Drinking the total number instead of the "to drink" number. Food gives you ~20%, so a 2.5 L total means about 2.0 L of actual liquid, not 2.5 L.

• Forgetting to bump activity and climate. The same 75 kg body needs ~2.2 L sedentary but ~3.1 L on a hot training day, so leaving both on default undershoots badly.

• Chugging a litre at once to "catch up" at night. Your kidneys clear roughly 800 to 1000 ml an hour, so spread cups across the day and stop force-drinking before bed.

Privacy