Which is the oldest of these three standard measurement systems?

The concepts of the foot, pound and gallon are very old, but their formulation into a precise system of weights and measures is comparatively recent. Moreover, this formulation was not done to a single worldwide standard: British Imperial deviates from US customary in some respects, and both are completely different from the metric system, as seen in the photo showing volume marks in the three systems.

The metric system dates from the adoption of the first well-defined system in France in 1795. It has come to be adopted in most of the world and was nearly adopted by the US: Thomas Jefferson requested artifacts from France that could be used to implement the metric system in the US: but the ship bringing them was blown off course and captured by pirates.

The British Imperial System was based on early English units, but was a complete, coherent system, first defined in the British Weights and Measures Act 1824, and later developed through further acts and amendments.

The United States customary units, also based on early English units, came later. The complete system was formalised and adopted in 1832. Some advocates of the US system saw the earlier metric system as atheistic. An official of the International Institute for Preserving and Perfecting Weights and Measures wrote that the US units were "a just weight and a just measure, which alone are acceptable to the Lord." His organisation even published music for a song proclaiming "down with every 'metric' scheme."