Infusion Time
How long the bag will take to run — and the clock time it finishes.
1000 mL at 125 mL/hr runs for 8 hours.
Same day, on a 24-hour clock.
Divide the volume left in the bag by the rate the pump is running at. A 1000 mL bag at 125 mL/hr takes 1000 ÷ 125 = 8 hours. Started at 08:00, it finishes at 16:00. Multiply any decimal part of an hour by 60 to get the minutes.
The reverse of a flow-rate calculation
Setting up an infusion asks “what rate delivers this volume in this time?”. Handing over or planning your round asks the opposite: “at this rate, when will the bag be empty?”. Both use the same relationship between volume, rate, and time — only the unknown moves.
Knowing the finish time matters for practical reasons: when the next bag needs to be ready, whether the line will run dry during a break, and whether the infusion will still be running at handover. It is also how you check that a bag hung earlier is running at the rate it should be.
Turning the decimal into minutes
Dividing rarely gives a whole number of hours. 700 mL at 150 mL/hr is 4.667 hours, and 0.667 of an hour is 0.667 × 60 = 40 minutes, so the run time is 4 hours 40 minutes. Reading “4.67 hours” as 4 hours 67 minutes is a common slip and pushes the finish time out by nearly half an hour.
Add the run time to the start time to get the completion time. If the total crosses midnight, the finish falls on the following day.
Worked example: 1000 mL at 125 mL/hr from 08:00
Divide, split the decimal, then add to the clock:
- 1 Read the volume left in the bag. The bag holds 1000 mL and is full.
- 2 Read the rate from the pump. The pump shows 125 mL/hr.
- 3 Divide volume by rate. 1000 mL ÷ 125 mL/hr = 8 hours exactly.
- 4 Convert any decimal part to minutes. There is none here. For 4.667 hours you would take 0.667 × 60 = 40 minutes.
- 5 Add the run time to the start time. 08:00 + 8 hours = 16:00. Document the expected completion time.
Run time for common volumes and rates
Volume divided by rate, shown as hours and minutes.
| Volume | Rate | Run time |
|---|---|---|
| 1000 mL | 125 mL/hr | 8 h 0 min |
| 1000 mL | 100 mL/hr | 10 h 0 min |
| 1000 mL | 80 mL/hr | 12 h 30 min |
| 700 mL | 150 mL/hr | 4 h 40 min |
| 500 mL | 75 mL/hr | 6 h 40 min |
| 250 mL | 100 mL/hr | 2 h 30 min |
| 100 mL | 200 mL/hr | 0 h 30 min |
Why the real finish time drifts
A calculated completion time assumes the rate never changes. In practice infusions are paused for medication, for the patient to mobilise, or by an occlusion alarm, and every pause pushes the finish later. A gravity line drifts even without interruption because flow depends on bag height and patient position.
Treat the result as a planning figure and re-check the volume remaining at each round. If a bag is well behind the predicted time, that is worth investigating — a partially occluded line or a rate that was reset can both hide behind a bag that is simply “running slow”.
This tool is a study aid for practising calculations. Infusion monitoring and documentation must follow the prescription and local policy.