IV Flow Rate
The millilitres per hour to program into an infusion pump.
Program 125 mL/hr to deliver 1000 mL in 8 h.
Useful when an order is written per minute, or for short pushes.
Divide the volume to be infused by the time it should run for, in hours. A litre ordered over 8 hours is 1000 ÷ 8 = 125 mL/hr, which is the number you enter on the pump. If the order is in minutes, convert to hours first.
What the pump actually needs
A volumetric infusion pump is programmed with two numbers: the volume to be infused and the rate in millilitres per hour. The rate is simply the total volume spread evenly over the ordered time, so the whole calculation is one division. Everything else — drop factors, drip chambers, counting — belongs to gravity infusions, not to pumps.
Orders are not always written as a rate. A prescription may say “1 litre normal saline over 8 hours” or “500 mL over 90 minutes”, and it is the nurse who converts that into a rate. Where the order names a rate directly, there is nothing to calculate — check it against the volume and the intended duration instead.
Partial hours
Times such as 90 minutes or 45 minutes have to become hours before dividing: 90 minutes is 1.5 hours, so 500 mL over 90 minutes is 500 ÷ 1.5 = 333.3 mL/hr. Dividing by 90 instead of 1.5 is the classic slip, and it produces a rate sixty times too small.
Convert any part-hours first: 30 min = 0.5 h, 45 min = 0.75 h, 90 min = 1.5 h. Most pumps accept one decimal place.
Worked example: 1000 mL over 8 hours
One division, then a plausibility check:
- 1 Note the volume to be infused. The bag holds 1000 mL of normal saline.
- 2 Convert the ordered time to hours. The order says 8 hours, so no conversion is needed. For 90 minutes you would use 1.5 hours.
- 3 Divide the volume by the hours. 1000 mL ÷ 8 h = 125 mL/hr.
- 4 Program the pump. Enter a volume to be infused of 1000 mL and a rate of 125 mL/hr.
- 5 Cross-check the duration. 1000 ÷ 125 = 8 hours, which matches the order — the arithmetic reverses cleanly.
Common infusion rates
Rate = volume ÷ time. Values are rounded to one decimal place.
| Volume | Time ordered | Rate (mL/hr) |
|---|---|---|
| 1000 mL | 8 hours | 125 |
| 1000 mL | 12 hours | 83.3 |
| 1000 mL | 24 hours | 41.7 |
| 500 mL | 4 hours | 125 |
| 500 mL | 90 minutes | 333.3 |
| 250 mL | 30 minutes | 500 |
| 100 mL | 30 minutes | 200 |
| 50 mL | 15 minutes | 200 |
Reading the rate back
Every flow-rate calculation can be checked by reversing it: volume divided by the rate should return the ordered time. If 1000 mL at 125 mL/hr gives 8 hours, the rate is right. This reverse check catches unit slips faster than re-reading the original sum.
Short infusions deserve extra care. A 50 mL antibiotic over 15 minutes runs at 200 mL/hr, a rate that would empty a litre bag in five hours — high numbers are expected for small volumes over short times, and are not in themselves an error.
This tool is a study aid for practising calculations. Pump settings must be programmed and independently verified by a qualified professional against the prescription.