The usual “short bond paper” size in Microsoft Word is 8.5 inches by 11 inches , which corresponds to the Letter paper size.

If you want it in centimeters for Word’s custom size box, that’s 21.59 cm (width) by 27.94 cm (height).

In Word, you can set this by going to Layout → Size → Letter (8.5″ x 11″) , or use More Paper Sizes and type 21.59 cm for width and 27.94 cm for height.