INR Calculator

How is INR Calculated?

INR can be calculated with the following variables:

1. Patient's prothrombin time


2. Control prothrombin time


3. International sensitivity index

• INR = International normalized ratio


• PPT = Patient's prothrombin time


• CPT = Control prothrombin time


• ISI = International sensitivity time

Understanding Your Results

The result from this INR calculator will be a single number. This number is the measure of how quickly your blood can clot. Generally, a normal range for INR in a healthy individual would be between 0.8 and 1.1. In certain scenarios a number around 2.5 to 3.5 would be considered normal, it is all dependent on what your doctor believes to be the best value for your current health.

How to Use the INR Tool

Calculating the INR of someone can be difficult. That is why we made this tool, to make it as simple and easy as possible to get that value. The steps include:

1. Enter the patient's prothrombin time in seconds.


2. Enter the control prothrombin time in seconds.


3. Edit the international sensitivity index value of 1.300 if necessary.


4. Hit calculate and get your INR results!

Example Calculation

Let's say some students in medical school need to calculate the INR of each other during a class project. They can use this tool to help them with that. They measure their prothrombin time is 11 seconds and the control is 12. To use this tool we will enter 11 into the first field and then 12 into the second field. We will leave the international sensitivity index value as it is.

We can now hit calculate to get the INR value for the student. We find that the INR value is .893 which is falls into the range of generally normal for a healthy individual.