Written calculation on paper (working out arithmetic by writing columns, as opposed to mental arithmetic).
小学生はまず筆算で繰り上がりの仕組みを学ぶ。
Elementary students first learn how carries work by doing written calculations.
大きな桁の足し算は筆算で確認した方が安全だ。
It's safer to check large-digit additions with written calculations.
電卓がないときは筆算で答えを出した。
When there was no calculator, I worked out the answer by hand.
Obsolete: used to mean writing together with arithmetic (an older term for combined literacy and calculation).
明治時代の教科書には算筆（筆算）を同時に教える例が見られる。
In Meiji-era textbooks there are examples of teaching writing and arithmetic (筆算) together.