Kids Water Intake Calculator
Estimate a child’s daily fluid needs from body weight using the Holliday-Segar maintenance-fluid method.
How it works
Holliday-Segar: 100 mL/kg for the first 10 kg + 50 mL/kg for the next 10 kg + 20 mL/kg for each kg over 20
The Holliday-Segar formula is the standard clinical estimate of daily maintenance fluid for children. It uses a tiered rate — generous for the first 10 kg of body weight, then tapering — because smaller bodies lose proportionally more water. The result is total fluid over 24 hours, which includes water in milk, food and other drinks, not just plain water. Hot weather, fever, vomiting or heavy activity all raise the requirement.
Worked example
A 40 lb child weighs 18.1 kg: 100 × 10 (first 10 kg) + 50 × 8.1 (next 8.1 kg) = 1,000 + 407 ≈ 1,407 mL, or about 6 cups of total fluid per day.
Frequently asked questions
Does this mean my child must drink that much plain water?
No — the figure is total fluid intake, including milk, soups, fruit and other drinks. Plain water only needs to make up the shortfall after those.
When should a child drink more than this?
During fever, diarrhoea, vomiting, hot weather or intense sport, fluid needs rise. If a child shows signs of dehydration — dark urine, dry mouth, unusual tiredness — offer more fluids and seek advice.
Is the Holliday-Segar method used for adults?
It is designed for children and is most accurate up to about 70–80 kg, above which it plateaus. Adults usually use simpler per-weight or per-calorie estimates instead.
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This is a general educational estimate, not medical advice. Every child grows, feeds and responds to medicine differently — for anything about your child’s health, growth, nutrition or medication, follow the guidance of your pediatrician.