# How To Calculate the PSI to LBS Multiplier for an APG Gauge

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Our digital pressure gauges can be set up using the “Custom Units of Measure” function to read in pounds. To do this, you’ll need to figure out the multiplier for converting psi to pounds based on area where the force is applied. The manufacturer of the ram or the hydraulics sometimes provides this. When it doesn’t, you’ll need to do a few calculations to figure it out.

A few years ago, a motorcycle design and manufacture company approached us about a 5000 psi digital pressure gauge. They wanted to measure pounds of force from a ram with a diameter of 5 inches.

Calculate the area of the ram used in the application:

In order to get the psi to lbs multiplier, we needed to calculate the area. The formula for this is area = pie X by the radius2 (A=πR2). So we multiply π (3.14) by 6.25 inches (radius of 2.5 inches2) to get 19.625 square inches.

Formula used to calculate pounds:

Next, we have to convert the total pounds of force to tons. 19.625 square inches at 5000 psi (19.625 X 5000) generates 98,125 lbs. Divide this by 2000 lbs, or one ton, and you get 49 tons.

To calculate the multiplier:

To get the multiplier that you’ll enter into the gauge, divide the tons (49) by the psi full scale (5000). This equals 0.0098. Enter that into the custom multiplier screen on the digital pressure gauge.

Here are steps to enter the multiplier into the gauge:

Step 1: Press the On/Off button once to enter the main setup menu.

Step 2: Press the Zero button to cycle through the options until UNITS is displayed.

Step 3: Press the Select button to access the Units setting options.

Step 4: Press Zero to cycle through the Units options until CUSTOM is displayed.

Step 5: Press Select to access the Custom Units setting.  A 5-digit conversion factor will appear with the first digit flashing.

Step 6: Press the Zero button to change the value of the flashing digit (options: 0-9).

Step 7: Press the Select button to accept the flashing digit and advance to the next digit. Repeat steps 6 and 7 as necessary.

Step 8: After the last digit is accepted by pressing Select, use the Zero button to scroll through the custom units of measure; LBF, KN, LBS, KG, and NEWTON.