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A siding calculator works out how much siding you need — in squares (100 sq ft) — from your total wall area minus the doors and windows, with a waste allowance for the cuts and overlaps. It also points you at house wrap, which covers the same net area.
Lap siding wastes more than you'd think because each course overlaps the one below, so the printed coverage isn't the wall area. The waste allowance handles that — bump it for gables and lots of openings.
Net wall area = gross wall area − openings. Squares = net area × waste multiplier ÷ 100. Siding is sold and quoted by the square; vinyl and fibre-cement lap siding typically want 10-15% waste because of the course overlap and end cuts.
160 ft of wall at 10 ft high is 1,600 sq ft; less 120 sq ft of openings and +12% waste, that's about 16.6 squares of siding.