Sip Siren
Recommended daily baseline
80 oz
- Millilitres
- 2,370 mL
- 8 oz cups
- 10 cups
Free Tool
Water intake calculator: how much water should you drink a day?
For most healthy adults, a practical daily target is half your body weight in pounds, drunk as ounces of water. A 160 lb (73 kg) person should drink about 80 oz — roughly 2,365 mL, or ten 8 oz cups — spread across the day at about one cup every 90 minutes.
Adjust from there: add about 12 oz on a moderately active day or 24 oz for intense exercise, increase the total by roughly 15% in hot and humid conditions, and add about 6 oz for every cup of coffee or energy drink. The calculator below does all four adjustments as you type, and the reference table lists targets by body weight if you'd rather just look yours up.
Calculate your daily water target
Not eight glasses — your number. Enter your weight, how hard you move, the air you live in and how much coffee you get through.
Ideal sip frequency
1 cup every 1 hr 30 min
That's about 10 cups of 8 oz spread across a roughly 14-hour waking day — steady sipping, not a litre before bed.
Last updated 27 August 2026 · Method and reference figures reviewed against the National Academies' intake guidelines.
These figures are general guidance for healthy adults, not medical advice. If you're pregnant, breastfeeding, or managing a kidney, heart or electrolyte condition, ask your doctor for your target.
Reference
Daily water intake by body weight
Baseline targets in a temperate climate with no caffeine, using the same method as the calculator. Find your weight, then read across to your activity level.
| Body weight | SedentaryDesk day | ModerateWorkout or on your feet | IntenseHard training |
|---|---|---|---|
| 100 lb45 kg | 50 oz1,480 mL · 6.2 cups | 62 oz1,830 mL · 7.8 cups | 74 oz2,190 mL · 9.2 cups |
| 120 lb54 kg | 60 oz1,770 mL · 7.5 cups | 72 oz2,130 mL · 9 cups | 84 oz2,480 mL · 10.5 cups |
| 140 lb64 kg | 70 oz2,070 mL · 8.8 cups | 82 oz2,430 mL · 10.2 cups | 94 oz2,780 mL · 11.8 cups |
| 160 lb73 kg | 80 oz2,370 mL · 10 cups | 92 oz2,720 mL · 11.5 cups | 104 oz3,080 mL · 13 cups |
| 180 lb82 kg | 90 oz2,660 mL · 11.2 cups | 102 oz3,020 mL · 12.8 cups | 114 oz3,370 mL · 14.2 cups |
| 200 lb91 kg | 100 oz2,960 mL · 12.5 cups | 112 oz3,310 mL · 14 cups | 124 oz3,670 mL · 15.5 cups |
| 220 lb100 kg | 110 oz3,250 mL · 13.8 cups | 122 oz3,610 mL · 15.2 cups | 134 oz3,960 mL · 16.8 cups |
| 240 lb109 kg | 120 oz3,550 mL · 15 cups | 132 oz3,900 mL · 16.5 cups | 144 oz4,260 mL · 18 cups |
| 260 lb118 kg | 130 oz3,840 mL · 16.2 cups | 142 oz4,200 mL · 17.8 cups | 154 oz4,550 mL · 19.2 cups |
In hot and humid conditions, add about 15% to any figure above. In dry or air-conditioned air, add about 8%. Add roughly 6 oz (177 mL) for each cup of coffee or energy drink.
The Evidence
What the official guidelines actually say
The most widely cited reference figures come from the U.S. National Academies (then the Institute of Medicine), which in 2004 set adequate intake for total water at 3.7 litres (125 oz) per day for men and 2.7 litres (91 oz) per day for women.
Here's the detail most hydration articles leave out: that's total water, from all food and drink combined. The panel found roughly 80% of intake comes from beverages and about 20% from food. So the drinking-only equivalent is closer to 100 oz for men and 73 oz for women — which is why a number quoted as "125 oz a day" is not a target you're supposed to reach with a glass.
The same report noted that people who are very physically active or who live in hot climates need more, and it deliberately declined to set one universal number. That's exactly why this calculator adjusts for body weight, activity, climate and caffeine instead of quoting a flat figure. For reference, its 80 oz result for a 160 lb sedentary adult sits between the beverage-only figures for women and men above.
The Method
How to calculate your daily water intake
Four steps, no app required. This is exactly what the calculator above does with your numbers.
-
1
Start from your body weight
Take half your body weight in pounds and drink that many ounces. A 160 lb person starts at 80 oz (2,365 mL). Weigh yourself in kilograms? Multiply by 2.2 first — 73 kg is 161 lb, so roughly the same 80 oz.
-
2
Add for activity
Sweat has to be replaced. Add about 12 oz (355 mL) for a moderately active day — a gym session, a long walk, a job on your feet — and about 24 oz (710 mL) for intense training or hard physical work.
-
3
Adjust for your climate
Heat and humidity push losses up by roughly 15%. Dry or heavily air-conditioned air — offices, planes, winter heating — costs you around 8% through your skin and breath without ever making you feel like you're sweating.
-
4
Offset caffeine, then split it into sips
Add about 6 oz (177 mL) per cup of coffee or energy drink. Then divide your final total by an 8 oz cup and spread those cups over roughly 14 waking hours. That interval — usually somewhere between 45 and 120 minutes — is the number that actually matters, because it's the one you have to act on all day.
FAQ
Water intake questions, answered
How much water should I drink a day for my weight?
A practical starting point is half your body weight in pounds, taken as ounces of water. A 150 lb person starts near 75 oz (about 2,200 mL, or 9 cups) per day; a 200 lb person starts near 100 oz (about 2,950 mL, or 12.5 cups). Add roughly 12 oz for a moderately active day or 24 oz for intense exercise, raise the total by about 15% in hot and humid weather, and add about 6 oz for each cup of coffee or energy drink.
How often should I drink water during the day?
Spread your target evenly across your waking hours instead of drinking it in a few large amounts. For a typical 80 oz target, that's ten 8 oz cups across about 14 waking hours — roughly one cup every 90 minutes. Steady sipping keeps you consistently hydrated; catching up with a litre at night mostly just interrupts your sleep.
Does coffee count toward your daily water intake?
Coffee does contribute fluid, but caffeine is a mild diuretic, so a cup of coffee isn't a one-for-one replacement for a cup of water. This calculator takes the practical route: add about 6 oz of water per caffeinated drink. That offsets the loss without pretending coffee is dehydrating you outright.
Is 8 glasses of water a day accurate?
Eight 8 oz glasses (64 oz, about 1,900 mL) is a rule of thumb, not a personal target. It ignores body weight, activity, climate and caffeine — so it under-shoots badly for a heavier or active person in hot weather, and over-shoots for a smaller, sedentary one. Calculating from your own inputs gives you a number you can actually aim at.
Why do I know my water target but still fail to hit it?
Knowing the number was never the problem. Standard hydration apps send a push notification you can swipe away in under a second, and within a few days your brain filters it out entirely. Sip Siren replaces the notification with a real iOS alarm built on Apple's AlarmKit that rings through Silent mode and Focus — and it only stops once you record a short video verifying you actually took a drink.
Knowing your target is only half the battle.
Almost nobody misses their water goal because they didn't know the number. They miss it because a push notification takes half a second to swipe away. If you ignore normal reminders, Sip Siren sounds real iOS alarms that break through Silent mode and Focus — and they won't stop until you record proof of drinking.
