Calculate your daily water intake based on weight, activity level and climate.
A water intake calculator estimates how much fluid you need each day, based on body weight, activity level, and climate. The famous "8 glasses a day" rule is a rough average — actual needs range from 1.5 L for a small sedentary person in a temperate climate to over 4 L for a heavy active person in a hot climate.
Hydration affects nearly every body function — circulation, temperature regulation, cognitive performance, kidney function, and exercise capacity. Even mild dehydration (1–2% of body weight in water loss) causes measurable drops in mood and physical performance.
W = 30 \text{ to } 40 \text{ mL/kg body weight}
Inputs: 70 kg adult · moderately active · normal climate
Yes — older "caffeine is dehydrating" advice has been disproved. Up to about 400 mg caffeine per day (≈ 4 cups coffee) does not produce a net fluid loss because the diuretic effect is mild and the fluid in the drink itself more than compensates. Excessive intake (8+ cups) does shift the balance, but for normal consumption, coffee and tea fully count.
Easiest check: urine colour. Pale straw yellow = well hydrated. Dark yellow or amber = drink more. Crystal clear = you may be slightly over-hydrated (rarely a problem). Other signs of mild dehydration: headache, fatigue, difficulty concentrating, dry mouth — all reversible with 500 mL of water within 15 minutes.
EMI Calculator Mortgage Calculator SIP Calculator Compound Interest GST / VAT Calculator Salary Calculator Unit Converter Currency Converter Scientific Calculator Concrete Calculator Paint Calculator Tile Calculator Calorie / TDEE Body Fat Macro Calculator O-Ring Sizes Bolt & Nut Sizes Pipe Sizes Wire Gauge AWG Needle Gauge Chart IV Cannula Sizes Suture Sizes Catheter French Sizes Drug Dosage See all 90+ calculators ›