Narrative:

I was ferrying aircraft X. An a&P had checked the plane out and made an agreement for purchase. Upon arrival; I was picked up by the seller; a CFI; and we drove to the hangar to inspect the aircraft. I was given the specifics of the aircraft and was told there were no issues with the aircraft. After our conversation I made a detailed inspection of the aircraft utilizing the checklist. Fuel quantity and quality were included in this inspection and it was verified that both tanks were indeed full to the top of the caps.I started the aircraft and taxied out after receiving instructions from ground. I performed a run up and all was as expected. I requested flight following for my planned route from ZZZ to ZZZ1 via direct. My direct route would have only a slight deviation around bravo airspace. Climb out was performed at approximately 2300 RPM at 500-800 RPM. My planned altitude was 6;500. However; cloud tops required 8;500 to avoid many deviations around tops after flying for a short time at 6;500. Per the performance tables I planned for a fuel burn of 6.2 gpm while in cruise as I flew at 2300 RPM and leaned the mixture. Considering a higher fuel burn during the climb of 8 gpm; my calculated endurance would give me an expected endurance of just over 5-1/2 hours with no reserve after considering the unusable amount of fuel in each tank.my estimated flight time enroute was just over 4 hours; leaving a reserve of just over 1 hour. In flight; no abnormalities were encountered in the operation of the engine. However; I did note that the right fuel gauge did not report as expected as it showed nearly full the entire flight. I made a mental note of this to report to the new owner. The last gauge reported near what would be expected along the route. As I began my decent into ZZZ1 I would enrich the mixture a little with each 1;000 ft. Of decent. I was handed over to the tower from approach. I was informed of regional jets that were departing ahead of my arrival and was cleared to land. I went through the before landing and landing checklist and set the aircraft up for landing. After reducing the throttle and lowering flaps; the engine quit without any hesitation. I immediately tried restarting the engine three times before declaring 'mayday; mayday; mayday engine out.' seeing trees to my right; the field short of the runway being very rough; I chose a flat hilltop to the left just off field for my landing.I performed a short field landing and came to stop very quickly as the hilltop was covered in high weeds. I had no injuries as I had on the seat belt and shoulder harness. I exited the aircraft and found no damage. After a few minutes I inspected the tanks and found them to contain very little fuel. As a side note; the aircraft had an aftermarket power flow exhaust system. While the manufacturer of the product makes claims of fuel savings at the same RPM settings; I did not include their claims in my fuel calculations.

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Original NASA ASRS Text

Title: C172 Pilot reported improper fuel readings and fuel burn; resulting in fuel exhaustion and an off airport landing.

Narrative: I was ferrying Aircraft X. An A&P had checked the plane out and made an agreement for purchase. Upon arrival; I was picked up by the seller; a CFI; and we drove to the hangar to inspect the aircraft. I was given the specifics of the aircraft and was told there were no issues with the aircraft. After our conversation I made a detailed inspection of the aircraft utilizing the checklist. Fuel quantity and quality were included in this inspection and it was verified that both tanks were indeed full to the top of the caps.I started the aircraft and taxied out after receiving instructions from Ground. I performed a run up and all was as expected. I requested flight following for my planned route from ZZZ to ZZZ1 via direct. My direct route would have only a slight deviation around Bravo airspace. Climb out was performed at approximately 2300 RPM at 500-800 RPM. My planned altitude was 6;500. However; cloud tops required 8;500 to avoid many deviations around tops after flying for a short time at 6;500. Per the performance tables I planned for a fuel burn of 6.2 GPM while in cruise as I flew at 2300 RPM and leaned the mixture. Considering a higher fuel burn during the climb of 8 GPM; my calculated endurance would give me an expected endurance of just over 5-1/2 hours with no reserve after considering the unusable amount of fuel in each tank.My estimated flight time enroute was just over 4 hours; leaving a reserve of just over 1 hour. In flight; no abnormalities were encountered in the operation of the engine. However; I did note that the right fuel gauge did not report as expected as it showed nearly full the entire flight. I made a mental note of this to report to the new owner. The last gauge reported near what would be expected along the route. As I began my decent into ZZZ1 I would enrich the mixture a little with each 1;000 ft. of decent. I was handed over to the Tower from Approach. I was informed of regional jets that were departing ahead of my arrival and was cleared to land. I went through the before landing and landing checklist and set the aircraft up for landing. After reducing the throttle and lowering flaps; the engine quit without any hesitation. I immediately tried restarting the engine three times before declaring 'Mayday; mayday; mayday engine out.' Seeing trees to my right; the field short of the runway being very rough; I chose a flat hilltop to the left just off field for my landing.I performed a short field landing and came to stop very quickly as the hilltop was covered in high weeds. I had no injuries as I had on the seat belt and shoulder harness. I exited the aircraft and found no damage. After a few minutes I inspected the tanks and found them to contain very little fuel. As a side note; the aircraft had an aftermarket Power Flow exhaust system. While the manufacturer of the product makes claims of fuel savings at the same RPM settings; I did not include their claims in my fuel calculations.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.