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Syringe pump rate calculation in mL/hr: method and worked examples

Stéphane Rodriguez, registered nurse in France since 2008, creator of Pocket Nurse · Updated 31 October 2026

Syringe pump orders scare students because they mix units: mg/hr, mg/kg/hr, micrograms. In practice, it all comes down to two steps.

The two-step method

Step 1: the syringe concentration

Concentration = amount of drug ÷ total volume in the syringe

Step 2: the rate

Rate (mL/hr) = ordered dose per hour ÷ concentration

Before dividing, always check that the ordered dose and the concentration are in the same unit (mg with mg, micrograms with micrograms).

The examples below use a fictional "drug": they teach the method, they don't give doses.

Example 1: order in mg/hr

Order: 2 mg/hr. Syringe: 50 mg in 50 mL.

1. Concentration: 50 ÷ 50 = 1 mg/mL
2. Rate: 2 ÷ 1 = 2 mL/hr

Example 2: a different dilution

Order: 3 mg/hr. Syringe: 20 mg in 40 mL.

1. Concentration: 20 ÷ 40 = 0.5 mg/mL
2. Rate: 3 ÷ 0.5 = 6 mL/hr

Syringe duration: 40 mL ÷ 6 mL/hr = 6.67 hr, so 6 hr 40 min. Handy to plan the next syringe.

Example 3: weight-based order (mg/kg/hr)

Order: 0.1 mg/kg/hr. Patient: 70 kg. Syringe: 50 mg in 50 mL.

1. Hourly dose: 0.1 × 70 = 7 mg/hr
2. Concentration: 50 ÷ 50 = 1 mg/mL
3. Rate: 7 ÷ 1 = 7 mL/hr

Syringe duration: 50 ÷ 7 = 7.14 hr, so about 7 hr 9 min.

Example 4: order in micrograms

Order: 300 micrograms/hr. Syringe: 5 mg in 50 mL.

1. Convert everything to micrograms: 5 mg = 5,000 micrograms
2. Concentration: 5,000 ÷ 50 = 100 micrograms/mL
3. Rate: 300 ÷ 100 = 3 mL/hr

Remember: 1 mg = 1,000 micrograms. A conversion error multiplies or divides the dose by a thousand.

Safety checks

• Same units before you divide.
• Label the syringe: drug, dose, volume, concentration, rate, date and time.
• Independent double check for high-alert drugs, per your unit's policy.
• Does it make sense? A rate of 70 mL/hr on a 50 mL syringe should stop you.

A calculation never replaces the order or your unit's protocol. If in doubt, get a check before you start the pump.

Frequently asked questions

What if the calculated rate is higher than the pump allows? The issue is usually the dilution: a more concentrated syringe means a lower rate. You never change a dilution on your own, it is prescribed or set by protocol.

How do I check a calculation when I'm alone at night? Work it backwards: rate × concentration should give you back the ordered hourly dose. If the numbers don't match, start again from the concentration.

Why so many errors with micrograms? Because the vial label is in mg and the order in micrograms, or the other way round. Write the unit next to every number throughout the calculation, not just at the end.

Should the calculation be written down? Yes. Concentration and rate go on the syringe label and in the record. A written calculation can be rechecked, a mental one is lost at handover.

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