Maintenance fluid calculator (4-2-1 rule)
Enter body weight in kilograms or pounds to get the hourly rate by the 4-2-1 rule and the daily volume by the Holliday–Segar method. It is an estimate for information, not a prescription.
Runs in your browser: nothing you enter is sent anywhere.
How to use it
- Choose kilograms or pounds and enter body weight.
- Read the hourly rate by the 4-2-1 rule and the daily volume by Holliday–Segar.
Holliday–Segar (per day):
- 100 mL/kg for the first 10 kg
- 50 mL/kg for the next 10 kg (11–20 kg)
- 20 mL/kg for each kg above 20
4-2-1 rule (per hour):
- 4 mL/kg for the first 10 kg
- 2 mL/kg for the next 10 kg
- 1 mL/kg for each kg above 20
Pounds are converted with 1 lb = 0.45359237 kg.
Worked example
A child who weighs 30 kg:
- Daily: 10 × 100 + 10 × 50 + 10 × 20 = 1000 + 500 + 200 = 1700 mL/day, or 70.8 mL/h.
- Hourly: 10 × 4 + 10 × 2 + 10 × 1 = 40 + 20 + 10 = 70 mL/h.
Common mistakes
- Using the 100 mL/kg rate for the whole weight: it applies only to the first 10 kg.
- Mixing up pounds and kilograms: 33 lb is 15 kg, not 33 kg.
- Treating the result as a prescription. This is an estimate for information; fluid orders come from the treating clinician, who also accounts for deficits and ongoing losses.
Frequently asked questions
What is the 4-2-1 rule?
An hourly version of Holliday–Segar: 4 mL/kg/h for the first 10 kg, 2 mL/kg/h for the next 10 kg and 1 mL/kg/h for every kilogram above 20. A 25 kg child gets 40 + 20 + 5 = 65 mL/h.
Why do the hourly rate and the daily volume ÷ 24 differ slightly?
The 4-2-1 rule rounds the daily figures for easy mental arithmetic: 100 mL/kg/day ÷ 24 is 4.17 mL/kg/h, not 4. Both rows are shown so you can see the difference, which is small.
Can I use it for adults?
The formula is often extended to adults, giving about 2500 mL/day at 70 kg, but it was developed for children. Adult fluid needs depend heavily on illness, kidney and heart function.
Is maintenance fluid the total a patient needs?
No. It covers normal daily losses only. Deficits from dehydration, ongoing losses such as vomiting or fever, and conditions needing restriction change the amount, and the choice of fluid matters too.