The handy Keystone Lintels Psi value calculator allows you to obtain a psi value with a few clicks of a button, free of charge. Generally this information takes a specialist company a few days to turn around.

We’ve created this handy step-by-step guide with accompanying video to take you through how to use the calculator.

  • Step 1: Using the dropdown menus, choose your cavity width, cavity fill, insulation and internal leaf selections.
  • Step 2: Select ‘Show Results’ and your psi value should now be calculated and appearing on screen.
  • Step 3: Email a certificate of your chosen psi value by selecting the ‘Email Certificate’ button and filling in the required details.

    Note: Elements that are constant feature on the top right of the page as a drop-down in case you need them.


    Energy Assessors can now directly input the lintel psi value into their SAP calculations and view the performance benefit. Specifically calculated Psi values will help lower the y value within the SAP calculation assisting Part L compliance.

    To ensure accuracy, all Psi value calculations have been generated by trained thermal modellers using Physibel Trisco software by the BRE.

    Go to Psi Value Calculator