if the FSR isnt very precise what would be a better option?
Strain gauges are what they use in electronic scales. But they are a little trickier to interface than the FSR. The signal is very small and requires amplification.
I used a simple mechanical balance in the Arduiwino 2.0. It was calibrated such that a 4-oz pour would tip the balance and trip a microswitch. I have also used ultrasonic sensors to measure the liquid level in the glass, but one drop of liquid splashed on the transducer is enough throw off the reading.
If you can describe what you are trying to do in more detail we might have some other suggestions.