I know what the OP was and have read the responses to it and it strikes me that someone has little experience of measuring fuel here.
The most sensible option would of course be upright tanks with capacitance gauges rather than flat and float to make dipsticks (and dipsticks) obsolete.
This not being the case in a 172 however it is probably worth buying a plastic dipstick for the same price as a few minutes in the air and then measure, mark, chisel and sand a stick until fulfilment arrives......and then of course keep wings level fore and aft and don't let it crossfeed wile dipping your stick.