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Calculator for determining the F or P values of thermal processes.

This versatile calculator can calculate the cumulative value of most heat processes. Instructions on how to use the calculator can be obtained by clicking the icon.help icon

A "new data grid" is required for each new calculation.

Before generating the data grid, the "start and end time" controls along with the "time interval" control should be used to define your input requirements.

Then adjust the reference temperature and Z-value and generate the data entry grid.

Use the edit control to add your temperature-values. Remember to click the update link to enter your value! The software will then calculate the equivalent lethality at the reference temperature and using the Trapezoid rule, the cumulative lethality for your process.

The F/P thermal process calculator can also be used to determine dry heat sterilisation, dry heat depyrogenation values, and whether requirements for pasteurization or guidelines for sous vide processing have been met provided the correct Tr and Z values have been used.

The no of log cycles that a designated  microbial  population has been reduced by heating can be calculated by dividing the F value by the D value at Tr. A 12 log cycle reduction is required for the reduction of spores of Clostridium botulinium in 'commercially sterile' low acid canned foods. Six log reductions are required for most pasteurization processes.  You can use the CSV import function to import your own data and the Z  and Tr values can be modified to model F or P values using given time / temperature inputs. 

Other easier to use calculators that have been designed to work with thousands of pasted time-temperature values or keyboard inputs are available. URLs are below. None of these offer the unique CSV file validation function of this calculator.

A calculator for determining the F or P value of a thermal process

Reference Temp, °C
Start-time, min
help icon
F value of process 0
End-time, min
Interval, min

help icon
Time [Min] Temp [C]Lethal Rate















Interested in downloading a Microsoft Excel Spread sheet for doing F or P calculations?

How to cite this article

Mullan, W.M.A. (2008) [On-line]: Available: Accessed:

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