The IV flow rate calculator determines the rate in millilitres per hour (mL/hr) to program into an infusion pump, given the total volume to be infused and the prescribed duration. This is the most common IV calculation nurses perform when setting up electronic infusion devices. The result should be entered directly into the pump — always verify the programmed rate against the physician's order before starting.
Pump rates for standard bag sizes over common infusion times. The formula is simply volume ÷ time in hours, but having the usual combinations to hand saves doing it twice at 3am.
| Volume | Over 1 hr | Over 2 hr | Over 4 hr | Over 8 hr | Over 24 hr |
|---|---|---|---|---|---|
| 1,000 mL | 1,000 | 500 | 250 | 125 | 42 |
| 500 mL | 500 | 250 | 125 | 63 | 21 |
| 250 mL | 250 | 125 | 63 | 31 | 10 |
| 100 mL | 100 | 50 | 25 | 13 | 4 |
| 50 mL | 50 | 25 | 13 | 6 | 2 |
Piggyback antibiotics are usually small volumes over 30 to 60 minutes, and the arithmetic catches people out because the time is under an hour — you divide by the fraction of an hour, so a 30-minute infusion doubles the hourly rate.
| Volume | Over 15 min | Over 30 min | Over 60 min | Over 90 min |
|---|---|---|---|---|
| 50 mL | 200 mL/hr | 100 mL/hr | 50 mL/hr | 33 mL/hr |
| 100 mL | 400 mL/hr | 200 mL/hr | 100 mL/hr | 67 mL/hr |
| 150 mL | 600 mL/hr | 300 mL/hr | 150 mL/hr | 100 mL/hr |
| 250 mL | 1,000 mL/hr | 500 mL/hr | 250 mL/hr | 167 mL/hr |
Worked through: 100 mL of an antibiotic over 30 minutes. Thirty minutes is 0.5 hours, so 100 ÷ 0.5 = 200 mL/hr. It looks like a fast rate on the pump, and it should — you're delivering a small bag quickly, not running a litre in.
Divide the total volume in mL by the infusion time in hours. For example, 500 mL over 4 hours = 500 ÷ 4 = 125 mL/hr. Program this rate into the infusion pump.
Yes. For blood products, divide the total volume by the prescribed infusion time. A standard unit of packed red blood cells (approx 300 mL) over 2 hours = 150 mL/hr. Always follow your institution's transfusion protocol and monitor the patient closely.
Divide the volume by the time in hours. Thirty minutes is 0.5 hours, so 100 mL over 30 minutes is 100 ÷ 0.5 = 200 mL/hr. Short infusions give high hourly rates because the pump rate describes what would run in an hour, not what's actually being given.
125 mL/hr. 1,000 ÷ 8 = 125, which is why it's such a common maintenance rate — a one-litre bag across a standard eight-hour shift.