The family hydration calculator
Six family members, six different needs, one 30-second form. Get a printable per-member plan for the fridge — free, no sign-up required to download.
One dashboard for the whole household.
Per-member goals, shared logs, one view. Vari+ covers you and 1 family member today — Family tier lands next.
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Every family calculator you find online gives you one number: 'Your family needs 9 L per day.' That number is useless — a household of four doesn't drink from one big water cooler. The grandmother needs 2 L, the 6-year-old needs 1.4, the parent needs 3, and the teenager needs 2.2. Telling the family '9 litres' means nothing happens. Telling each person their personal target — and giving you one printable page that has all six — changes what your fridge looks like tomorrow morning. This page explains how the family calculator works, what to expect in the output, how to turn the result into a real routine, and how the free PDF download fits into your week.
Why a family calculator beats six separate calculators
Shared context, different numbers
A 6-year-old and a 42-year-old live in the same climate, do the same weekend hike, and drink from the same pitcher at dinner. But they need very different amounts. One calculator that outputs per-person numbers is the only honest answer.
Routines are household-level, targets are individual
You serve water at breakfast to everyone. You put bottles in backpacks. The household rhythm is shared; what goes into each bottle is personal. A family calculator produces both — the individual ml and the shared schedule.
Printable beats app-only
The fridge is the single highest-traffic surface in a family home. A printed plan stuck to the fridge gets seen 20+ times a day. An app plan gets checked maybe twice. This calculator's primary output is a PDF for that reason.
Every family member has edge cases
Pregnancy, breastfeeding, kid on a sports team, grandparent on diuretics, teen who skips breakfast. The calculator handles the obvious ones; warnings on the page flag when an edge case needs the doctor instead.
What the calculator computes
Per-member daily target in ml
Adults get 35 ml/kg baseline with activity and climate modifiers. Kids get IOM pediatric bands by age. Output is rounded to the nearest 50 ml and clamped to safe ranges (800-5000 ml).
Source: Institute of Medicine + NAS hydration guidance
6-slot daily schedule
Morning wake-up, breakfast, mid-morning, lunch, afternoon, dinner, wind-down. Amounts proportional to the person's target. Timed to cluster at transitions (meals, school start/end) where kids and adults are both present.
Recommended bottle size + refill count per person
Picks the smallest bottle (500/600/750/800/1000 ml) that fits the target in 4 daily refills. Four is the best habit loop — enough to feel regular, few enough to remember.
7-day habit tracker printable
A grid for each family member covering the next 7 days. Each day has 4 tick-boxes representing the 4 daily bottle refills. Goes on the fridge.
Warning signs by age band
The PDF includes age-specific dehydration warning signs for every member, plus when-to-see-doctor thresholds. So even if the plan isn't followed perfectly, the safety net is printed.
How to use the calculator's output over a week
- Run the calculator once and print the PDF — keep it simple, don't re-run it every day
- Put the printed plan on the fridge at eye level (not behind magnets or school art)
- Buy the bottle sizes the PDF recommends — mismatched sizes cause refill-count drift
- Set one phone reminder per day for the adult: 'pour the 3 PM glass for everyone'
- Re-run the calculator when any family member's situation changes: new sport, pregnancy, new medication
- On hot days, add 20% across the board — don't re-run the calculator, just pour more
- Check urine colour once a day for the whole household; pale straw by 3 PM = plan is working
- Share the household Vari account (when available) so each member's intake rolls up in one view
Your personalised plan — as a printable PDF
Take 30 seconds to get your family-tuned daily water target, a 6-slot schedule, and a 7-day tracker for the fridge. Free. No credit card.
Build my plan →When the calculator alone isn't enough
Signs of Dehydration
- Any family member on medication that affects fluids (diuretics, ACE inhibitors, SGLT2 inhibitors)
- Pregnancy with severe morning sickness that prevents keeping fluids down for 24+ hours
- A child with a diagnosed chronic illness where fluid restriction or boost has been prescribed
- Post-surgery recovery — doctors usually give a specific daily target that may differ from the calculator
- Family member with CKD, CHF, or kidney stones — fluid target must come from the nephrologist / cardiologist, not the calculator
- Any family member whose daily intake is consistently 50%+ below their calculated target — conversation needed
- Unexpected symptoms — the calculator isn't diagnostic, it's a baseline. Persistent dizziness, fatigue, or unusual thirst need a clinician, not more water
Frequently Asked Questions
How does the family hydration calculator work?
You enter age, weight, and activity level for each family member. The calculator applies pediatric bands for children (IOM guidance) and 35 ml/kg for adults, with activity and climate adjustments. Output: a per-person daily target in ml + a routine that covers everyone in the household.
Do I have to sign up to see the result?
No. The result shows immediately on the page. If you want the printable PDF version with a 7-day tracker, you can download it without an account. If you want the plan emailed and saved to a Vari account, that's an optional second step.
Is this calculator accurate for kids of different ages?
It uses the Institute of Medicine pediatric bands (1.1 L for toddlers, 1.4 L for ages 4-8, 1.9 L for 9-13). These are widely used by pediatricians as a baseline. For kids with medical conditions, your doctor's specific target always overrides the calculator.
Can I see targets for a pregnant or breastfeeding family member?
Yes — the calculator adds 300 ml/day for pregnancy and 700-1000 ml/day for breastfeeding to the adult baseline. Select the matching option in the adult form.
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