C152 PLT DEPARTED ON A PLEASURE FLT; BELIEVING THE ACFT FUEL QUANTITY TO BE SUFFICIENT. UPON RETURNING; THE ACFT WAS FUELED AND THE PLT REALIZED THAT HE HAD ONLY 2 GAL OF USABLE FUEL REMAINING AT SHUTDOWN.

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I DEPARTED PAO ARPT FOR A LEISURE FLT. DURING THE PREFLT INSPECTION; I CHKED THE FUEL LEVELS VISUALLY SINCE I COULDN'T FIND THE DIPSTICK INSIDE THE PLANE. THE FUEL INSIDE THE TANKS WAS VISIBLE RIGHT AWAY. IT WAS DOWN FROM THE TOP ABOUT 1 1/2 INCHES IN BOTH TANKS. I THEN CHKED THE FUEL INDICATORS AND THEY WERE POINTING 3/4 EACH. I CALCULATE THAT IF THE PLANE TAKES 26 GALLONS; IT SHOULD HAVE HAD 9.5 GALLONS IN EACH WING. I THEN CALCULATED THAT IF I WAS GOING TO BE FLYING FOR 2 HRS THAT WOULD HAVE TAKEN ME 12 GALLONS PLUS 1 GALLON OF THE GND OPS. SO 13 GALLONS PLUS 2.5 GALLONS OF UNUSABLE FUEL -- THAT'S 15.5 GALLONS OUT OF 19 GALLONS. I THOUGHT THE PLANE HAD ANOTHER 3.5 GALLONS OF USABLE FUEL. I CHKED THE FUEL LEVELS IN ALL PHASES OF FLT; AND AT THE END OF THE FLT THE NEEDLES WERE POINTING A LITTLE LESS THAN 1/4 IN EACH TANK -- JUST BEFORE I SHUT THE PLANE DOWN. WHEN THE FUEL TRUCK FILLED THE PLANE UP IT TOOK 22.5 GALLONS OF GAS TO TOP IT OFF; WHICH LEFT ME WITH ONLY 2 GALLONS LEFT OF USABLE FUEL; LESS THAN THE LEGAL MINIMUM. I WILL NEVER TAKE OFF AGAIN WITHOUT KNOWING THE EXACT AMOUNT OF FUEL IN EACH WING; AND IF I HAD NO WAY OF KNOWING THAT AMOUNT; I WILL MAKE SURE THE TANKS ARE TOPPED OFF BEFORE DEP. I WILL ALSO NEVER RELY ON THE FUEL GAUGES. THEY ARE UNRELIABLE AND SHOULD NEVER BE USED TO CALCULATE HOW MUCH FUEL IS ONBOARD.