Converting Force Measurement to Pressure

A zip-tie like structure squeezes an elastic part. I can measure a force that is related to the squeezing pressure. I need to create a calibrator that would allow me to correlate the force to the squeezing pressure. I have a zip-tie like structure, which when pulled, squeezes an elastic part. Think of it like a having a zip-tie around your finger. I can measure a force that is related to the squeezing pressure. This relationship between force and pressure is quite linear. I would now need to create a calibrator that would enable me to correlate between the measured force (N) to the pressure (Pa) that is imposed to the elastic part. The diameter of the zip-tie is about 22mm and it squeezes to about 17mm diameter. Now, I first started to think that I would have some inflatable balloon with fixed pressure. The zip tie wouldn't move when the pressures match. I would prefer to keep this calibrator relatively simple at first stage, so any crazy, easily built ideas are welcome ;-).