Applying Formulas to Columns With ARRAYFORMULA

Normally if you want a calculation in every row, you write one formula and drag it down. That works, but it leaves hundreds of copied formulas that you must extend whenever new data arrives.

Google Sheets offers a better way: ARRAYFORMULA. One formula in one cell computes the entire column at once and grows automatically.

ARRAYFORMULA tells Sheets to apply a formula across whole ranges instead of single cells. The result spills down to fill as many rows as the input range has.

So instead of =A2*B2 repeated 100 times, you write one formula referencing A2:A and B2:B, and the answers fill themselves in.