What is the "one foot" of calligraphy and painting works?

One foot equals one square foot (33.3x33.3cm).

Common dimensions of calligraphy works:

Four-foot whole 135cmx68cm 8 square feet

Four feet square, 68 cm x68 cm, 4 square feet.

Four feet apart 135cmx34cm 4 square feet.

Three feet, one piece, 50cmx 100cm 4.5 square feet.

Six feet180cm x100cm18 square feet.