Maintenance Fluid Calculator (4-2-1 Rule)

Verified formula Updated Jun 2026 Private — runs on your device

Verified formula Private

Hourly maintenance fluid

65.0

Daily maintenance fluid: 1,560

For general information only — not financial, tax, legal or medical advice. Verify before you rely on it.

How to use the Maintenance Fluid Calculator (4-2-1 Rule)

The Maintenance Fluid Calculator (4-2-1 Rule) works out your hourly maintenance fluid, along with 1 related figure in an instant. Enter body weight and the result updates as you type — it is free, needs no sign-up, and runs entirely in your browser so your figures stay private.

Enter the body weight.
Read off your hourly maintenance fluid, together with daily maintenance fluid — the calculator updates automatically, with no button to press.

Worked example

For example, with body weight of 25 kg, the hourly maintenance fluid is 65.0.

Inputs used
Body weight	25 kg

Results
Hourly maintenance fluid	65.0
Daily maintenance fluid	1,560

Results are estimates for educational use, not professional advice.

Frequently asked questions

It estimates hourly maintenance fluids: 4 mL/kg for the first 10 kg, 2 mL/kg for the next 10 kg, and 1 mL/kg for each kg beyond 20.

Multiply the hourly rate by 24. A 25 kg patient needs about 65 mL/hr, or roughly 1560 mL per day.

The 4-2-1 rule is widely taught for both children and adults as a starting estimate of baseline fluid needs.

No. Actual fluid orders depend on losses, illness and lab values and must be set by a clinician.

Enter the body weight. Read off your hourly maintenance fluid, together with daily maintenance fluid — the calculator updates automatically, with no button to press.