IV drip rate calculator

Drip rate in drops per minute is the volume in millilitres multiplied by the drop factor of the giving set, divided by the time in minutes. Macrodrip sets deliver 10, 15 or 20 drops per millilitre and microdrip sets deliver 60, so the same prescription gives different rates on different equipment.

When to use the iv drip rate calculator

Use whenever an order gives a volume and a duration rather than a pump rate. The drop factor comes from the giving set itself and is printed on the packaging, commonly 20 drops/mL for clear fluids and 15 for blood.

The iv drip rate formula

Rate in mL/hr = volume in mL ÷ time in hours. Drops per minute = (volume in mL × drop factor in drops/mL) ÷ time in minutes.

Worked example

One litre is to run over 8 hours through a set delivering 20 drops/mL. In mL/hr: 1000 ÷ 8 = 125 mL/hr. In drops/min: (1000 × 20) ÷ 480 = 41.7, so 42 drops per minute.

The mistake that costs marks

Time units are where these questions are won and lost. The mL/hr formula needs hours and the drops/min formula needs minutes, so converting once and then using the wrong denominator is the standard error. Drop factor also changes with the giving set, so it must be read from the question rather than assumed.

Study aid, not a clinical tool

This calculator exists so you can learn the method and check your working for an examination. It is not medical advice and not clinical decision support, and it must not be used to make a decision about a real patient. Verify any result against your local formulary, the product literature and a qualified pharmacist. Our medical disclaimer sets out the full position.

Calculators you will usually need alongside this

Most questions that reach for one of these reach for another a step later, so these are the three that most often pair with it.

• Infusion rate converter (mcg/kg/min to mL/hr) — mcg/kg/min to mL/hr
• Dilution calculator (C1V1 = C2V2) — Dilution
• Osmolarity calculator — Osmolarity

Keep going

Calculations are only half of what examinations test. The other half is knowing why a drug does what it does, which is what decides whether a number you calculated is even the right number to be calculating. Start with Best pharmacy calculators. The drug class pages cover the mechanism behind the number, or browse the rest of the free calculators and try the practice questions.