What is the standard weight-based UFH protocol?

The most widely used protocol gives an IV bolus of 80 units/kg (max 10,000 units) followed by a continuous infusion starting at 18 units/kg/hr (max 1,000 units/hr). Subsequent adjustments are made every 6 hours based on the aPTT result using a validated nomogram.

Why is there a maximum cap on the bolus and infusion?

Caps prevent excessive heparin exposure in very large patients. Most protocols set the bolus cap at 10,000 units and the infusion cap at 1,000–1,250 units/hr, though institutional protocols vary. Always follow your site-specific nomogram.

What body weight should be used — actual or ideal?

Standard UFH weight-based protocols use actual body weight (ABW). Some institutions use adjusted body weight for morbidly obese patients (BMI ≥ 40), but this varies. Confirm with your institution's heparin policy.

What bag concentration does this tool assume?

The mL/hr calculation assumes the common pharmacy preparation of 25,000 units in 250 mL (100 units/mL). If your pharmacy uses a different concentration — such as 25,000 units in 500 mL (50 units/mL) — divide the units/hr result by your actual concentration to get the correct mL/hr.

Is this calculator a replacement for clinical judgment?

No. This tool is for educational and reference purposes only. Heparin dosing requires aPTT monitoring, clinical assessment of bleeding risk, renal function, platelet counts (to watch for HIT), and adherence to validated institutional protocols. Always verify orders with a licensed pharmacist or physician.

When should heparin NOT be used?

Absolute contraindications include active major bleeding, heparin-induced thrombocytopenia (HIT), and severe thrombocytopenia. Relative contraindications include recent surgery, intracranial hemorrhage, and severe liver disease. Clinical evaluation is mandatory before initiating anticoagulation.

Heparin Dosing Calculator

Name: Heparin Dosing Calculator
Availability: InStock
Author: Nham Vu

Enter patient weight to calculate the standard UFH bolus dose (80 units/kg, max 10,000 units) and initial IV infusion rate (18 units/kg/hr, max 1,000 units/hr).

Patient Weight

Actual Body Weight (kg)

Standard protocols use actual body weight.

Bag Concentration (units/mL)

Protocol Reference

Bolus 80 units/kg

Bolus cap 10,000 units max

Initial infusion 18 units/kg/hr

Infusion cap 1,000 units/hr max

For educational purposes only — not a substitute for clinical judgment. Heparin is a high-alert medication. All doses must be verified by a licensed pharmacist or physician and managed with aPTT monitoring per an institutional protocol.

Enter patient weight and click Calculate Dose

IV Bolus Dose

Calculated (80 units/kg)

—

units

Dose to give

—

units IV push

Initial Continuous Infusion

Rate (units/hr)

—

units/hr

Pump rate

—

mL/hr

Calculation Summary

Patient weight —

Bolus (80 units/kg) —

Infusion (18 units/kg/hr) —

Bag concentration used —

Clinical Next Steps

1. Obtain baseline aPTT, PT/INR, CBC, and platelet count before initiating therapy.
2. Recheck aPTT 6 hours after bolus or any rate change.
3. Adjust infusion rate per your institution's validated aPTT-based heparin nomogram.
4. Monitor platelet count every 2–3 days to detect heparin-induced thrombocytopenia (HIT).
5. Verify all doses with a licensed pharmacist or physician before administration.

Summary

Enter patient weight to calculate the standard UFH bolus dose (80 units/kg, max 10,000 units) and initial IV infusion rate (18 units/kg/hr, max 1,000 units/hr).

How it works

Enter the patient's actual body weight in kilograms.
The bolus dose is calculated as 80 units/kg, capped at a maximum of 10,000 units.
The initial infusion rate is calculated as 18 units/kg/hr, capped at a maximum of 1,000 units/hr.
The infusion rate is also expressed in mL/hr using a standard 100 units/mL bag concentration (25,000 units in 250 mL).
Review the results panel and note the prominent medical disclaimer before use.
Subsequent dose adjustments must be guided by aPTT monitoring per your institution's heparin nomogram.

Use cases

Estimate the initial UFH bolus and drip rate for a patient with DVT or PE.
Support nursing or pharmacy staff during anticoagulation initiation.
Cross-check a heparin order at the bedside before administration.
Practice weight-based heparin calculations in a clinical pharmacy or nursing education setting.
Quickly determine the mL/hr drip rate when using a standard 25,000 units/250 mL bag.
Serve as a reference when reviewing heparin protocol adherence.
Support clinical students learning anticoagulation pharmacology.
Verify calculated doses during rapid response or code situations.

Frequently Asked Questions

Last updated: 2026-07-23 · Reviewed by Nham Vu