Daily Water Intake Calculator — How Much Water Per Day?

“Eight glasses a day” ignores your size, your activity, and your climate — a 55 kg office worker and a 95 kg roofer in summer do not need the same water. Enter your weight, activity level, and climate below and this calculator gives you a personal daily target in millilitres, glasses, and bottles, plus a spread-out drinking schedule so you are not chugging a litre at 9 pm. It is general guidance, not medical advice: illness, pregnancy, and medication can change what you need, so check with a clinician if any of those apply.

How it works

Enter your weight, pick your activity level, and tick the hot-climate box if it applies, then press Calculate Water Intake. The calculator starts from the common 35 ml-per-kilogram baseline, scales it by activity (×1.0 sedentary, ×1.15 moderate, ×1.30 active), and adds 500 ml for hot or humid conditions. It then converts the total into 250 ml glasses and 500 ml bottles and spreads it into a per-waking-hour pace, so the target feels like a routine instead of a chore.

Everyday uses

• Desk workers — stop guessing and set a real daily target.
• Athletes — scale intake up on training days.
• Summer — adjust for heat instead of running dry.
• New routines — pair the schedule with meals to build the habit.
• Families — calculate a sensible target for each person.