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Thermal Hold Equivalence Calculator

Calculate equivalent time at a reference temperature for one constant product-temperature hold, using a supplied z-value. This does not estimate botulism risk.

Use this result well

Inputs that matter
Constant-temperature hold time, Product hold temperature, Reference temperature, Model z-value, and 1 more
Output to expect
Equivalent time at the reference temperature
  • Check the units and required inputs before comparing results.
  • Keep the assumptions with a copied result so you can reproduce the calculation later.
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Reference & details

How it works

Calculate the relative modeled rate

A positive z-value is the temperature increase corresponding to a tenfold change in the modeled rate. The temperature difference and z must use the same unit.

Relative rate = 10^((T − Tref) / z)

Source: FDA CVM Guidance #245, thermobacteriology definitions

Apply one constant hold

Multiply hold minutes by the relative modeled rate. This represents one constant product-temperature interval and excludes heating/cooling ramps.

Equivalent reference minutes = hold minutes × relative rate

Keep the scope of the calculation clear

The result supplies no organism-specific reduction or risk verdict. It does not model temperature distribution, heat penetration or a full canning process.

Updated: September 2026

Example Scenarios

Use 10 min at 110°C, reference 120°C and z = 10°C.

→ Relative modeled rate 0.1; equivalent time 1 min at 120°C.

Use 10 min at 120°C with reference 120°C.

→ Equivalent reference time is 10 min for any positive z-value.

Use 10 min at 230°F, reference 248°F and z = 18°F.

→ Equivalent time remains 1 min at the reference temperature.

Common Mistakes to Avoid

Entering the canner setting as the product temperature

Use actual product temperature at the relevant measurement location. The tool does not calculate heat transfer.

Adding 32 when converting a z-value

A z-value is a temperature difference. Multiply a Celsius difference by 1.8 for Fahrenheit, without adding 32.

FAQ

No. It calculates a specified constant-temperature model. A food safety decision needs the complete applicable process and evidence.

No. They are arithmetic examples, not an organism/product validation or recipe.

No. It handles one constant-temperature hold only.

No. The calculator supplies no required target or microbial reduction and does not assess process adequacy.

Use the applicable established model and actual product-temperature measurement. Home canning should follow the complete tested recipe and canner instructions.

About Thermal Hold Equivalence Calculator

Compare thermal exposure under a specified mathematical model. Enter product temperature and time, plus the model’s reference temperature and z-value; the result reports equivalent reference minutes.