C150 pilot reported they ran out of fuel during flight and landed safely in a field.

Narrative

While on a personal flight; the engine stopped suddenly. I performed the emergency procedures checklist; and selected a farmer's field below me to perform a landing in. I glided down and landed in the field uneventfully; which resulted in no damage to the aircraft or property damage and no injuries to myself or any bystanders. After an extensive walkaround and inspection of the engine compartment; which found no anomalies; I checked the fuel tanks and discovered that only the amount listed as unusable fuel (approx. 3.5 gals) in the POH remained on board.Before departure; I onboarded an amount of fuel that would have given me an estimated 30 minute reserve at my planned altitude. On this flight; I deviated from my intent to fly high (9;000 ft. MSL) and made a snap decision to fly along the river for sightseeing because it ended up being a nicer day outside than forecast. I simply forgot that the fuel burn while flying for prolonged periods at low altitude (between 500-1000 ft. AGL) is higher.I have learned many lessons; but my biggest takeaways from this incident will be to more closely stick to my flight planned routes/altitudes and to increase my personal fuel margin from the legal minimum of 30 minutes to a 45 minute or 1 hour fuel reserve.