GA pilot reported fuel exhaustion during a cross country flight required them to make an off-airport landing. Pilot stated there were no injuries or damage.

Narrative

On a cross country flight between Location A and Location B I experienced fuel exhaustion in my aircraft. I was 9 miles from ZZZ when it appeared I had run out of gas in all of my fuel tanks. As I was only approximately 1k ft AGL at the time of exhaustion; I had very little time to deal with the situation at hand. I attempted to make an abandoned airfield just to the north and within the outer ring of ZZZ1's Class Charlie. While maneuvering to make the airfield; and noting my depleting airspeed; I quickly ascertained I best land my aircraft straight ahead; in a farmers field. Landing was uneventful; no aircraft damage occurred; and no injuries whatsoever. After assessing the situation and determining the best course of action; I contacted a local tow service company. They moved my aircraft to the aforementioned airfield. I did a thorough inspection of my aircraft; serviced it with fuel; and proceeded to my original destination (ZZZ). Prior to my next flight; I once again did an inspection; this time more thorough than the last. Once again; there was no damage to the aircraft noted; so I proceeded to fly my aircraft back to Location A; without incident.After returning home; I sat down and thought about what went wrong. Obviously; I had overestimated the amount of fuel in my tanks. I figured I had a good 14 gallons in each of my wingtip tanks. However; after refueling them each with 10 gallons; it appears this is where my overestimating took place. The 10 gallons in each side; to my recollection; appeared to be more than what I had assumed was 14 gallons. I rarely utilize these tanks on a day-to-day basis; so I feel I need to gain a better site picture of what a less-than full wingtip tank looks like. I also plan to construct a dipstick for these tanks; as I don't believe one is available on the open market. It's no excuse; merely an explanation as to why I could've possibly not known how much fuel they contained.