4 to 20-mA devices in industrial settings generally use 24-V DC as the power source.
You put a 500 or 250 Ohm precision resistor in the DC circuit and measure the DC voltage across the resistor. A 500 Ohm resistor gives you 10-volts at 20-mA.
24-V DC is chosen as it allows several measuring devices to be on the same circuit, for example, a chart recorder and a SCADA analogue input module.
If your pressure sensor will work off a lower voltage, you can scale down things.
A 125 Ohm resistor at 20-mA will give you a full scale output voltage of 0.5 at 4-mA and 2.5-V at 20-mA. You have to offset the 0.5-V to make it sensible.
The specification of the 4 to 20 device will determine the working voltage you need to use.