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Heparin Drip Calculator (units/hr to mL/hr)

Calculate a heparin infusion rate in mL/hr from units/hr or a weight-based order in units/kg/hr, and the bolus dose in units.

kg
units
mL
units/kg

Enter the values: the answer and every step appear here as you type.

Formula

Concentration (units/mL) = units in the bag ÷ mL in the bag

units/hr = units/kg/hr × weight (kg)

mL/hr = units/hr ÷ units/mL

Bolus (units) = units/kg × weight (kg)

How to calculate it step by step

  1. Find the concentration: for 25,000 units in 250 mL, 25,000 ÷ 250 = 100 units/mL; for 25,000 units in 500 mL, 50 units/mL.
  2. For a weight-based order, multiply the units/kg/hr by the weight in kg.
  3. Divide the units/hr by the concentration to get mL/hr.
  4. Calculate any bolus in units (units/kg × kg) and round it as your protocol directs.
  5. Adjust the rate only according to the aPTT or anti-Xa results and the protocol.

Worked examples

Example 1. Order: heparin infusion at 1,300 units/hr. Available: heparin 25,000 units in 250 mL. At what rate in mL/hr will you set the pump?

  1. Concentration: 25,000 units ÷ 250 mL = 100 units/mL.
  2. 1,300 units/hr ÷ 100 units/mL = 13 mL/hr, rounded to 13 mL/hr.

Answer: 13 mL/hr

Example 2. Order: heparin 18 units/kg/hr IV. The patient weighs 77 kg. Available: heparin 25,000 units in 500 mL. At what rate in mL/hr will you set the pump?

  1. Concentration: 25,000 ÷ 500 = 50 units/mL.
  2. 18 units/kg/hr × 77 kg = 1,386 units/hr.
  3. 1,386 ÷ 50 = 27.72 mL/hr, rounded to 27.7 mL/hr.

Answer: 27.7 mL/hr

Rounding

Round the pump rate to the tenth of a mL/hr. Bolus and rate adjustments are often rounded to the nearest 100 units or 50 units per protocol.

Common mistakes

  • Mixing up the two common premixed concentrations (100 units/mL and 50 units/mL).
  • Using the weight in pounds, or a different weight from the one your protocol specifies (actual or dosing weight).
  • Confusing a heparin flush (10 or 100 units/mL) with therapeutic heparin vials (1,000 units/mL or more): this mix-up has caused fatal errors.

Nursing safety points

  • Heparin is a high-alert medication: an independent double check of the order, the concentration, the dose and the pump is required in most facilities.
  • Monitor the aPTT or anti-Xa, the platelet count (heparin-induced thrombocytopenia) and signs of bleeding.
  • Protamine sulfate is the reversal agent.

Frequently asked questions

How do you calculate a heparin drip in mL/hr?

Divide the units per hour by the units per mL. For 18 units/kg/hr in an 80 kg patient: 18 × 80 = 1,440 units/hr; with 25,000 units in 250 mL (100 units/mL), 1,440 ÷ 100 = 14.4 mL/hr.

What is the concentration of a 25,000 unit heparin bag?

25,000 units in 250 mL is 100 units/mL; 25,000 units in 500 mL is 50 units/mL.

How do you calculate a heparin bolus?

Multiply the bolus dose in units/kg by the weight in kg. 80 units/kg for 80 kg = 6,400 units, then round as your protocol says.