Pi (or ∏) refers to a constant numerical value 3.14, that relates the circumference of a circle to its diameter. Used as far back as the ancient Egyptians and Babylonians, the constant was so-named in 1706 by William Jones after the Greek letter for p, being the first word for perimeter.
We use pi in soft furnishings to calculate the circumference or perimeter of a circle or part of a circle for trimmings and edgings, say on tablecloths, lampshades, cushions, and to work out the radius ends of a bed cover.
To find the circumference of a 200cm diameter circle, the maths is: 2 x pi x radius (to find the radius divide the diameter by two)= 2 x 3.14 x 100 = 628 cms
See also tau.