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.
Reviewed against the cited sources · How pages are checked
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.
When the time is in hours, divide the volume by the hours. When it is in minutes, either convert to hours first (divide by 60) or multiply the volume by 60 and divide by the minutes, as the working column does. The last two columns show the same answer rounded to the tenth and to a whole number. Pumps and programs differ on which they want.
| Volume | Time | Working | To the tenth | Whole number |
|---|---|---|---|---|
| 1,000 mL | 8 hr | 1,000 ÷ 8 | 125 mL/hr | 125 mL/hr |
| 500 mL | 6 hr | 500 ÷ 6 | 83.3 mL/hr | 83 mL/hr |
| 250 mL | 90 min | 250 × 60 ÷ 90 | 166.7 mL/hr | 167 mL/hr |
| 50 mL | 20 min | 50 × 60 ÷ 20 | 150 mL/hr | 150 mL/hr |
| 1,000 mL | 24 hr | 1,000 ÷ 24 | 41.7 mL/hr | 42 mL/hr |
| 100 mL | 45 min | 100 × 60 ÷ 45 | 133.3 mL/hr | 133 mL/hr |
Take the 45-minute row slowly. 45 minutes is 0.75 hours, and 100 ÷ 0.75 = 133.3. A common slip is to divide by 45 and get 2.2 mL/hr, which would leave a 45-minute antibiotic running for nearly two days. If the pump rate looks absurdly low for a short infusion, the time has almost certainly been left in minutes.
Most volumetric pumps accept rates to one decimal place, and many nursing programs round mL/hr to the tenth. Others round to a whole number. Use the rule your program or facility sets, and apply it once, at the end. If the order is written as a dose per hour rather than a volume, as with heparin, insulin or many drips, the mL/hr has to be worked out from the concentration first. That is a different calculation: see the mcg/kg/min calculator and the heparin and insulin practice.
Before starting, check that the rate, the VTBI and the drug or fluid on the pump match the order and the bag. Smart pumps with drug libraries catch some errors, but only when the right drug and concentration are selected in the first place.
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.
It depends on the pump and your program. Most pumps accept one decimal place, and many nursing programs round mL/hr to the tenth (83.3 mL/hr), while others use whole numbers (83 mL/hr). Follow the rule your program or facility uses and round only the final answer.
Divide the minutes by 60 to get hours, then divide the volume by that figure. For 100 mL over 45 minutes: 45 ÷ 60 = 0.75 hours, and 100 ÷ 0.75 = 133.3 mL/hr. Equivalently, multiply the volume by 60 and divide by the minutes.