IV THERAPY
Heparin drip rate calculator
Turn a weight-based heparin order into a pump rate — enter the ordered dose in units/kg/hr, the patient’s weight, and the bag’s total units and volume to get the mL/hr, plus the full dimensional-analysis setup behind the answer. Every number comes from your order; no protocol doses are built in. Free, no signup, runs in your browser.
Interactive calculator
Heparin drip rate calculator
Enter the patient weight, the ordered weight-based dose (units/kg/hr), and the heparin bag (total units and volume) to calculate the pump rate in mL/hr, and see the worked setup below. Everything comes from your order — no protocol doses are built in. Results update as you type.
Result
Enter weight, ordered dose (units/kg/hr), and the bag’s total units and volume to see the concentration, infusion rate, pump rate, and the worked setup.
For education and practice only. Heparin is a high-alert medication. This tool is a study aid, not a substitute for clinical judgment, a drug reference, or institutional policy — and it contains no protocol or nomogram doses. Infusions are titrated to aPTT or anti-Xa on an institution-specific protocol; verify every value and perform an independent double-check before administering.
How it works
Weight-based heparin, by dimensional analysis
A weight-based heparin drip is pure unit math: scale the ordered dose to the patient’s weight to get units/hr, then divide by the bag’s concentration to get the pump rate in mL/hr. The calculator supplies the arithmetic — you supply the order.
Bag concentration (units/mL)
concentration = bag units ÷ bag volume (mL)
Read the total units and volume off the bag label and divide. A bag of 25,000 units in 500 mL is 50 units/mL. Concentrations differ between facilities, so always use the actual label.
Infusion rate (units/hr)
units/hr = dose (units/kg/hr) × weight (kg)
Multiply the ordered dose by the patient’s weight in kilograms. If weight is in pounds, convert first (lb ÷ 2.2 = kg) — the calculator does it and shows the step.
Pump rate (mL/hr)
mL/hr = infusion rate (units/hr) ÷ concentration (units/mL)
Divide the units/hr you need by the bag’s units/mL to get the rate you program into the pump. Round to the precision your pump and protocol allow, commonly the tenth.
Optional loading bolus (units)
bolus units = bolus dose (units/kg) × weight (kg)
Only when a bolus is ordered. Multiply the units/kg bolus by weight to get the units. Boluses are usually drawn from a concentrated vial per policy, not from the drip bag.
Worked example
A heparin drip calculation, step by step
The order
Heparin infusion at 18 units/kg/hr. The bag is 25,000 units in 500 mL. The patient weighs 80 kg. What pump rate do you set?
The setup
- 1. Concentration: 25,000 ÷ 500 = 50 units/mL.
- 2. Infusion rate: 18 × 80 = 1,440 units/hr.
- 3. Pump rate: 1,440 ÷ 50 = 28.8 mL/hr.
Answer: 28.8 mL/hr (round per your pump/protocol).
Reading the result
The 28.8 mL/hr is what you program into the pump for the drip. If the same protocol also ordered an 80 units/kg loading bolus, that is 80 × 80 = 6,400 units — drawn from a concentrated vial per policy, not pushed from the 500 mL bag.
Enter 80 kg, 18 units/kg/hr, 25,000 units, and 500 mL in the calculator above to see this exact worked setup returned. Add the 80 units/kg bolus to see the 6,400 units appear.
From here, the drip is titrated to the aPTT or anti-Xa on your institution’s nomogram — the arithmetic gets you to the starting rate, not the therapeutic endpoint.
Common questions
Weight-based heparin drips, explained
- What is a weight-based heparin drip?
- A weight-based heparin infusion is an IV drip ordered as a dose per kilogram per hour (units/kg/hr) rather than a fixed rate, so the amount scales to the patient's body weight. The provider or a protocol specifies the units/kg/hr; you multiply by the patient's weight in kilograms to get the infusion rate in units/hr, then convert that to a pump rate in mL/hr using the bag's concentration.
- How do I find the bag concentration in units per mL?
- Divide the total heparin units in the bag by the bag volume in milliliters: concentration (units/mL) = total units ÷ volume (mL). For a bag labeled 25,000 units in 500 mL, that is 25,000 ÷ 500 = 50 units/mL. Always read the concentration off the actual bag label rather than assuming a standard mix — concentrations vary between facilities.
- How do I calculate the pump rate in mL/hr from units/kg/hr?
- Two steps. First, infusion rate (units/hr) = ordered dose (units/kg/hr) × weight (kg). Second, pump rate (mL/hr) = infusion rate (units/hr) ÷ concentration (units/mL). For example, 18 units/kg/hr × 80 kg = 1,440 units/hr; with a 50 units/mL bag, 1,440 ÷ 50 = 28.8 mL/hr. Round to the precision your pump and protocol allow (commonly the tenth).
- What is the role of the heparin loading bolus?
- Some protocols start therapy with a one-time loading dose (bolus) ordered as units/kg to reach a therapeutic level quickly before the continuous drip takes over. Bolus units = bolus dose (units/kg) × weight (kg) — for example, 80 units/kg × 80 kg = 6,400 units. Boluses are usually drawn from a concentrated vial per policy, not pushed from the infusion bag, so the primary bolus answer is in units. Not every order includes a bolus; give one only when it is ordered.
- Why is heparin titrated to aPTT or anti-Xa instead of a fixed rate?
- Heparin's effect varies from patient to patient, so the infusion is adjusted (titrated) to a lab target — the aPTT or an anti-Xa level — following the ordering facility's protocol or nomogram. That nomogram tells you when and how much to change the rate or give a rebolus based on each lab draw. This calculator only does the arithmetic for the rate you are setting right now; it does not contain any protocol doses and does not replace the nomogram or the ordering provider's judgment.
- Is this heparin calculator safe to rely on, and is it free?
- It is completely free, needs no account, and runs entirely in your browser, so it works on a phone — but heparin is a high-alert medication, and a math check is not a substitute for the required safety steps. Verify every entered value against the order and the bag label, and perform an independent double-check with a second nurse per institutional policy before administering. This is a study and practice aid only, not medical advice, and it has no protocol doses built in — every number comes from the order you enter.
Keep practicing the med-math
More infusion and dosage practice
A heparin drip is one flavor of IV rate math. Practice general drip rates with the IV drip rate calculator, work broader weight-based dosing with the full dosage calculator, read the dosage study guide, or explore the other free calculators.
This calculator and all study material on this site are provided for practice and study only — they are not medical advice or a substitute for clinical judgment, a drug reference, or institutional policy. Heparin is a high-alert medication titrated to aPTT or anti-Xa on an institution-specific protocol; this tool has no protocol doses built in. Verify every value and perform an independent double-check before administering. NCLEX® is a registered trademark of the National Council of State Boards of Nursing, Inc. (NCSBN), which does not endorse or sponsor this site.