Heparin drip calculator: from units/kg/h to mL/h
For healthcare professionals and students. Check results against your local protocols and clinical judgement; this tool does not give medical advice. Follow your institution’s heparin nomogram.
This heparin drip calculator does the arithmetic of a weight-based unfractionated heparin infusion: it turns the bolus in units/kg and the infusion rate in units/kg/h from your protocol into total units, units per hour and the pump rate in mL/h for the bag you are using. A second mode applies a nomogram rate change in units/kg/h to the current pump rate.
It deliberately contains no default protocol. Heparin regimens differ by indication (venous thromboembolism, acute coronary syndromes, other uses), by institution and by monitoring method, so every dose, cap and adjustment must be typed from your own approved nomogram. That keeps the tool useful for teaching and for double-checking without suggesting a dose.
How to use the Heparin Drip Calculator
- Choose Bolus and starting rate or Rate change.
- Enter the dosing weight your protocol specifies, in kg or lb.
- Copy the heparin units in the bag and the bag volume from the label to get the concentration.
- Enter the bolus (units/kg), any maximum, the vial strength if the bolus comes from a vial, and the starting rate (units/kg/h) with any maximum — or, for a change, the current pump rate and the change from your nomogram.
- Read the mL/h and the working, and have the calculation independently checked before programming the pump.
Heparin Drip Calculator features
No built-in protocol
Every protocol field starts empty; nothing is calculated until you enter your own values.
Any bag strength
Concentration from units in the bag ÷ volume, so 100 units/mL, 50 units/mL or any other strength works.
Caps applied visibly
Optional maximum bolus and maximum starting rate are applied and announced when they change the result.
Bolus volume
Shows the bolus volume from the bag, or from a vial when you enter its strength.
Nomogram rate changes
Converts a change in units/kg/h into the new units/h and mL/h, with an optional re-bolus, and blocks a rate of zero or below.
Typo checks
Rejects a units/h figure typed into a units/kg/h box and flags unusually large values for review.
The arithmetic, step by step
Worked example with test values (hand-calculated, not a recommendation): a protocol bolus of 80 units/kg and starting rate of 18 units/kg/h — the values of the original weight-based nomogram by Raschke RA et al., Ann Intern Med 1993;119(9):874–881 — for an 80 kg dosing weight with 25,000 units in 250 mL (100 units/mL) gives a bolus of 6,400 units and 18 × 80 = 1,440 units/h = 14.4 mL/h. Many current protocols use different values, caps or anti-Xa monitoring; use yours.
- Concentration = units of heparin in the bag ÷ bag volume (mL).
- Bolus (units) = bolus (units/kg) × dosing weight (kg), then reduced to the maximum if your protocol sets one. Bolus volume = units ÷ concentration of the bag or vial used.
- Infusion (units/h) = rate (units/kg/h) × dosing weight (kg), capped if your protocol sets a maximum.
- Pump rate (mL/h) = units/h ÷ concentration.
- Rate change: current units/h = current mL/h × concentration; new units/h = current units/h + change (units/kg/h) × weight; new mL/h = new units/h ÷ concentration.
Common errors this tool helps catch
- units/h entered as units/kg/h. Typing 1,440 into a units/kg/h box would multiply the dose by the weight again; values above 60 units/kg/h are rejected.
- Wrong bag concentration. 25,000 units in 250 mL and 25,000 units in 500 mL differ by a factor of two in mL/h.
- Forgetting the protocol cap. If your nomogram caps the bolus or starting rate, enter it so the result reflects it.
- Using the wrong weight. Some protocols specify actual, adjusted or capped weight; enter the one yours requires.
- Rounding. Results are shown to 0.1 mL/h; check how your pumps and policy round.
Heparin Drip Calculator FAQ
How do you calculate a heparin drip rate in mL/h?
Multiply the protocol rate in units/kg/h by the dosing weight to get units/h, then divide by the bag concentration in units/mL. The heparin drip calculator above shows each step with your numbers.
How do I work out the heparin concentration?
Divide the units in the bag by the volume. 25,000 units in 250 mL is 100 units/mL; 25,000 units in 500 mL is 50 units/mL.
Why is there no default dose?
Heparin protocols differ by indication and institution, and heparin is a high-alert medicine. The tool only does the arithmetic for the values you enter from your approved nomogram.
How do I apply a nomogram rate change?
Choose “Rate change”, enter the current pump rate in mL/h and the change in units/kg/h from your nomogram (negative to decrease). The tool converts it to the new mL/h.
Can this be used for other infusions?
The maths is general, but this page is written and checked for heparin. For gravity drips there is a drip rate calculator, and for insulin concentrations an insulin units to mL converter.