Step by step
The question
Question: change 2 ft² to square inches.
1 Change the length
This square is 1 foot on each side.
Its area is 1 square foot.
1 foot is 12 inches.
So each side is 12 inches long.
2 Change the area
So the square holds 12 rows of 12 small squares, each 1 square inch.
So 1 square foot is 12 inches times 12 inches.
12 times 12 is 144.
So 1 ft² = 144 in².
Not 12: the 12 comes in twice.
3 Multiply
Each square foot is 144 square inches.
We have 2 of them, so we multiply: big unit to small unit.
Careful!
Times 12 only changes a length.
A square has two sides to change: times 12, and times 12 again.
2 times 144 is 288.
So 2 ft² = 288 in².
4 Check
Let's check: go back the other way.
Divide by 144.
We get 2 square feet again.
So it is right!
Let's look back.
First: change the length.
Then: change the area.
Then: multiply.
Last: check.