Area is length × width. Perimeter is the distance all the way round.
Step 1: Let's Learn
Read it, or press Listen and follow the words.
They answer different questions
Area covers the inside. Perimeter goes round the edge. Both numbers stay on screen.
Finding a missing side
If the area is 48 and one side is 6, the other side is 48 ÷ 6.
Same perimeter, different area
A 1 by 11 rectangle and a 6 by 6 square both have a perimeter of 24, but very different areas.
Two formulas, two questions
Area of a rectangle is length × width, and it answers how much surface is inside. Perimeter is 2 × (length + width), and it answers how far it is round the edge. The formulas are short, but they answer genuinely different questions.
Where each formula comes from
Area multiplies because the squares form an array of rows and columns. Perimeter doubles the sum because a rectangle has two lengths and two widths. Neither formula is arbitrary, and both can be rebuilt from a sketch in seconds if you forget them.
The units tell you which you found
Area comes out in square units, perimeter in plain length units. If a perimeter answer carries "square" in its unit, the wrong formula was used. Writing units on every answer turns this into an automatic check.
Using a formula backwards
Given the area and one side, divide to find the other. Given the perimeter and one side, halve the perimeter and subtract. Formulas run in both directions, and being able to work backwards is what turns them from recipes into tools.
Step 2: Try It Yourself
Both numbers are always shown, so they cannot be confused.
Area · squares inside
48
Perimeter · walk around
28
8 × 6 = 48 · 8 + 6 + 8 + 6 = 28
Area counts the cm inside. Perimeter measures the walk all the way round.
Step 3: Watch an Example
One step at a time.
Watch Leo Find a Missing Side
A rectangle has an area of 48 square cm and one side of 6 cm.
- Step 1
He knows area is length × width.
Step 4: Your Turn
Practice makes it stick.
The Garden
Problem 1 of 3
A garden is 9 m by 7 m. What is its area, in square metres?
square metres
The Fence
Problem 2 of 3
The same 9 m by 7 m garden. How much fence goes all the way round?
metres
The Missing Side
Problem 3 of 3
A rectangle has an area of 54 and one side of 9. How long is the other side?
Area or Perimeter?
1 of 4
Area of a 12 by 5 rectangle?
2 of 4
Perimeter of a 12 by 5 rectangle?
3 of 4
Area is 72, one side is 8. How long is the other?
4 of 4
Do two rectangles with the same perimeter always have the same area?
Step 5: Quick Check
Show what you know.
Question 1 of 2
Area of an 11 by 6 rectangle?
Question 2 of 2
Perimeter of an 11 by 6 rectangle?
What You Learned
- Area is length × width. Perimeter goes round the edge.
- A missing side is found by dividing the area.
- The same perimeter can give very different areas.