Dosage Calculation · Topic 10 of 10
IV Rate Calculation
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IV flow rates
Two formulas, picked by how the fluid runs: a pump runs in mL/h, a gravity drip in drops per minute (gtt/min).
Set the order. Watch it drip.
Worked example
Pump or gravity drip?
| Infusion pump | Gravity drip | |
|---|---|---|
| Unit | mL/h | gtt/min |
| Formula | mL ÷ hours | mL × drop factor ÷ minutes |
| Drop factor | Not needed | Needed — printed on the tubing package |
| Rounding | Tenth or whole number — as the device and policy allow | Whole drops — 0.5 or more rounds up |
Drop factors
Read it off the tubing package
Other math you'll see
Common errors
At the bedside
Overload is most likely in older adults. Electronic infusion pumps are recommended in all settings to cut infusion errors.
Keep it on time
Hours for a pump, minutes for a gravity drip — mix them up and the rate is 60 times off.
Sources · Clinical Nursing Skills 13.3 Intravenous Infusion (OpenStax) · Clinical Nursing Skills 13.2 Intravenous Device Insertion (OpenStax) · Introduction to IV Flow Rates and Infusion Time (WisTech Open) · Clinical Nursing Skills 13.1 Principles of Intravenous Therapy (OpenStax) · Guidelines for Safe Use of Smart Infusion Pumps (ISMP) · Follow your facility's protocol for IV infusions and pump rounding.
IV Rate Calculation
IV flow rate comes from volume and time — but the unit depends on the delivery method. A pump speaks mL/hr; a gravity drip speaks gtt/min and needs the tubing's drop factor.
IV flow rate is computed from the prescribed volume and infusion time, with the unit set by the delivery method. An infusion pump is programmed in mL/hr (volume divided by time in hours), so no drop factor is needed. A gravity (manual) drip with no pump is counted in gtt/min and DOES require the tubing's drop factor. Always confirm the calculated rate against the actual order before starting.
Key Distinctions
Choose the formula by delivery method, then read the drop factor off the tubing package. Macrodrip tubing (10, 15, or 20 gtt/mL) is for routine or rapid infusions; microdrip tubing (60 gtt/mL) is for precise, low-volume infusions. Because microdrip is 60 gtt/mL and there are 60 min/hr, microdrip gtt/min equals mL/hr.
Clinical Pearl
Pump = mL/hr (volume over hours, no drop factor); gravity drip = gtt/min (volume x drop factor over minutes). Microdrip is 60 gtt/mL, so its gtt/min equals mL/hr.
Knowledge Check
3 quick questions on the must-knows for this topic.
An infusion pump is programmed in which unit?
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