Water Intake Calculator
Last updated: June 2026 · Free · No sign-up required
Enter values above and click Calculate to see your result instantly.
Quick reference
Baseline water by weight:
| Body weight | Approx. daily water |
|---|---|
| 120 lb (54 kg) | ~1.9 L / 64 oz |
| 150 lb (68 kg) | ~2.4 L / 80 oz |
| 180 lb (82 kg) | ~2.9 L / 96 oz |
| 210 lb (95 kg) | ~3.3 L / 112 oz |
monitor_weight A starting point, not a diagnosis
This calculator gives you the same number a clinician would compute by hand from your inputs. It is informational, never a substitute for a doctor. If a result surprises you, write it down and discuss it at your next appointment — that conversation is the goal, not a verdict from a webpage.
science Built from peer-reviewed formulas
Every health calculator on CalcaTools uses an equation from the WHO, NIH, ACOG, CDC, or a published peer-reviewed paper. The exact citation is in the "Formula & methodology" section. We re-check sources quarterly and update the page when guidance changes — the "Last reviewed" date is at the top.
volunteer_activism Designed for real people
Health calculations only help if you can actually use them. We use plain-English labels (no jargon), accept both metric and US units, and show what a "normal" range looks like alongside your result — so you understand what the number means, not just what it is.
lock Private by design
Your weight, height, age, pregnancy details, and any other health input never leave your browser. Calculations run client-side; nothing is logged or stored on our side. We don't want your medical data — we just want the formula to work for you.
Interpretation guide
Adjust your intake:
| Factor | Adjustment |
|---|---|
| Exercise | +12–24 oz per 30 min |
| Hot climate | Increase to replace sweat |
| Pregnancy/breastfeeding | Higher needs |
| High-water foods | Count toward total fluids |
Formula & methodology
Formula: Approx daily water (oz) = body weight (lb) x 2/3; add ~12–24 oz per 30 min of exercise
A common estimate for daily water is about two-thirds of your body weight in pounds converted to ounces (or roughly 30–35 ml per kg). The calculator adjusts for exercise, climate, and life stage. These are general targets — thirst, urine color, and activity are good day-to-day guides. Food and other beverages also contribute to total fluid intake, so you don't need to hit the number with plain water alone.
Authoritative source: https://nap.nationalacademies.org/read/10925/chapter/6