The adhesion power for all adhesives products is mentioned in PSI. PSI is a unit of pressure (pounds per square inch). Our tester is measuring pounds force, Lb is a force unit.
So You can't convert pounds to pounds per square inch (psi). One is force and one is pressure. But If you know the area over which the force is spread, then you can divide the force by the area and get pounds per square inch (psi).
So I said if I apply 400 lbs in a 4 sq. inch platen, I will have a 100PSI presure on it.
If my adhesion power is 50PSI, using a 4 square inch platen I will apply a force up to 200lbs to un glue it. Com-Ten has disposable 2.25”discs, 2.25” and 4" reusable discs available for purchase for adhesion tests.

A  2.25” diameter disc has an area of 4 sq inch platen. So use a ratio of 4 when using those discs. Com-Ten has also disposable 4" diameter reusable discs . A disc 4” diameter is 12,6 sq inch platen. So use a ratio of 12,5 when using those discs. The bigger discs need to be used for low power adhesion in order to have more accurate results.

How do I choose the right pull tester?
Depending on the air barrier material and the wall material, the manufacturer recommends a minimum pull strength value (adhesion value), most of the time in psi. Below is a list of pull test values in lb depending on the size of the disc you stick on the material.

Minimum adhesion value Equivalent pull force with 2.25in diameter disc Equivalent pull force with 4in diameter disc
16 psi 64 lb 201 lb
20 psi 79 lb 251 lb
24 psi 96 lb 301 lb
28 psi 111 lb 352 lb
32 psi 127 lb 402 lb
40 psi 159 lb 502 lb
48 psi 191 lb 603 lb
56 psi 223 lb 703 lb

We offer different models of pull testers:
- Digital gauge: high accuracy (0.5% of the full scale). It allows a test of any type of air barrier material with a 1000lb gauge capacity.
- Analog gauge: accuracy 2% of the full scale. A gauge is recommended for test between 20% and 80% of its capacity (for example between 200lb and 800lb for a 1000lb capacity analog gauge). It means that you can not use a 1000lb gauge to measure low values.