C172 PLT MISCALCULATES FUEL REQUIREMENTS AND LANDS WITH APPROX 7 MINS OF USABLE FUEL.

Narrative

I DEPARTED EARLY AFTERNOON. DURING PREFLT; I NOTICED THE TANKS WERE NOT QUITE FULL; BUT ENOUGH TO MAKE THE FLT THERE WITH 2+ HRS RESERVE AND PLANNED TO REFUEL AT DEST. UPON ARR; I NOTICED NO ONE WAS WORKING THE FBO DUE TO LUNCH. ONCE I RETURNED TO THE ARPT FROM MY LUNCH; THE LINE MAN INFORMED ME THAT THEY DID NOT ACCEPT THE ONLY METHOD OF PAYMENT I HAD AVAILABLE. I CARRIED OUT MY PREFLT AND DETERMINED AT THAT TIME WITH THE GIVEN FUEL AND BURN RATE I WOULD BE ABLE TO MAKE MY DEST JUST ABOVE FAA FUEL MINIMUMS. ENRTE; THE WINDS WERE STRONGER THAN FORECAST AND CLOUDS REQUIRED ME TO FLY LOWER THAN ANTICIPATED. ABOUT 30 MI FROM DEST; THE R TANK INDICATOR WAS INDICATING A LITTLE UNDER 1/8 TANK WITH THE L TANK INDICATION SLIGHTLY MORE THAN 1/4. FROM THESE INDICATIONS; I BELIEVED THAT I HAD SUFFICIENT FUEL TO MAKE DEST ON TIME AND JUST WITHIN FUEL RESERVES. UPON LNDG; I WAS INFORMED THAT MY FUEL TANKS IN FACT HELD ONLY 1/2 GALLON ABOVE USABLE FUEL; EQUALING APPROX 7 MINS OF CONTINUED ENG OP. THIS OCCURRENCE HAS DRIVEN HOME THE POINT OF NOT RUSHING AND TO NEVER TRUST FUEL GAUGES. IN MY HASTE TO RETURN; I FORCED MYSELF TO GAMBLE WITH MY LIFE. HOWEVER; NEVER AGAIN WILL I MAKE SUCH A MISTAKE.