Front brake pad replace: calipers piston

[dslc]

We have an old Yaris that I plan to replace the front brake pads on soon. And am just wondering ...
What length G/C-clamp would I need to push the piston back into the calipers? (I have a 75mm one: would that suffice?)
Also, will I need to push the pistons back even if I'm not replacing the pads straight away? I plan to just to just take the calipers off to see what sort of state the old pads are in - rather than replacing them immediately.

[WeeYari]

75mm clamp would be too small.

For just removing the calipers to inspect the pads you do not need to compress the piston to reinstall. You will then also be able to see just how big a clamp you will need when the time comes.

[yarrr]

You can see how much pad is left without taking anything more than the wheel off. Yes 75 is too small.

[dslc]

Wee Yari and yarr: I appreciate the responses. You're both right - the 75mm is a bit too short. In the end I used a 150mm clamp - but, depending on how worn the pad is, I think a 100mm might have sufficed.
Anyway, pads now changed. If I decide to change the rotors, I might be back with more questions.
cheers