Will 20,000 medical charts fit into 1640.42 linear feet. each chart is 12x12 inches.
What you need to know is the thickness of a chart, including any folder, etc. If they vary, you need average thickness.
The use of linear feet (or meters) ignores the width and height of the file (but assumes they fit in the cabinet, and that only thickness matters. 1640.42" is 19685", so on average, each chart would have to be a little less than 1" thick (0.984" to be precise).
Going back to the 500 m, each chart has to be less than 25 mm thick, on average.
I have a trapezium with parallel sides 90 feet and 50 feet and sides 150 foot 6 inches and want to know the square meterage of the block.
The figure may be decomposed into a rectangle 50' long and two right triangles wuith a base of 20' and hypotenuse of 150.5' The unknown height is sqrt(150.5² - 20²) = 149.17'. The area is that height times 0.5*(50 + 90) = 10441.6 ft²
Since a foot is legally defined as 0.3048 m,
10441.6 ft² x (0.3048 m/ft)² = 970 m²
If you want square meters, it might be easier to measure in meters than to convert.