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Common Core Math4th GradeMeasurement & Data

4.MD.3: Area and Perimeter Formulas

Also written as 4.MD.A.3 and CCSS.MATH.CONTENT.4.MD.A.3 · Cluster: Solve problems involving measurement and conversion of measurements.

Make 4.MD.3 Graph PaperAll 28 4th Grade Math Standards

The Official Wording

Apply the area and perimeter formulas for rectangles in real world and mathematical problems. For example, find the width of a rectangular room given the area of the flooring and the length, by viewing the area formula as a multiplication equation with an unknown factor.

Common Core State Standards, Grade 4, Measurement & Data · Read it at the source · Checked October 14, 2026

What 4.MD.3 Means in Plain English

Fourth graders use A = l × w and P = 2 × l + 2 × w instead of counting squares, and run them backward: a garden with 30 feet of fence and a 9-foot side must be 6 feet wide.

A missing side turns the area formula into a multiplication with an unknown factor, which is division (4.NBT.6). In 5th grade the same thinking stacks into volume, V = l × w × h (5.MD.5), and in 6th grade it finds the area of triangles (6.G.1).

4.MD.3 I Can Statements

  • I can find the area of a rectangle with A = l × w.
  • I can find the perimeter of a rectangle with a formula.
  • I can find a missing side from the area or perimeter.

4.MD.3 Worked Example

One rug, both formulas: the area hides a missing side, and the trim around the edge is the perimeter.

Problem

A rectangular rug covers 48 square feet of floor and is 8 feet long. How wide is it? How many feet of trim go all the way around its edge?

A 48 square foot rug, 8 feet long
  1. Area is length times width. The length and the area are known, so the width is the missing factor.8 × w = 48
  2. Find the missing factor with division, or with the 8s facts.48 ÷ 8 = 6, so w = 6 feet
  3. Trim goes around the edge, so that is perimeter: two lengths and two widths.P = 2 × 8 + 2 × 6
  4. Multiply, then add.16 + 12 = 28 feet
AnswerThe rug is 6 feet wide, and it needs 28 feet of trim.

Check it: Area: 8 × 6 = 48 square feet, as given. Perimeter: walk the edges, 8 + 6 + 8 + 6 = 28 feet.

Common Mistakes with 4.MD.3

Answering a trim question with the area

An 8 by 6 rug given 48 feet of trim

Try this: Ask what is being covered and what is being walked around. Covering is area in square units, edges are perimeter in plain units.

Stopping at half the perimeter

P = 8 + 6 = 14 feet

Try this: Label all four sides on the drawing before adding. Opposite sides of a rectangle match, so two labels become four.

Multiplying to find a missing side

48 × 8 = 384, so the rug is 384 feet wide

Try this: Write the formula with a box for the unknown: 8 × □ = 48. A missing factor is found by dividing, never by multiplying again.

Where 4.MD.3 Fits

Comes Before3.MD.7Relate area to multiplication by tiling rectangles.3.MD.8Solve perimeter problems, including rectangles with the same area and different perimeters.
Alongside4.NBT.6Divide to find a missing factor, like 48 ÷ 8.4.NBT.5Multiply two-digit sides, like a 24 by 15 foot room.
Comes Next5.MD.5Find volume with V = l × w × h.6.G.1Find the area of triangles and other polygons by composing rectangles.

Practice 4.MD.3

Graph Paper GeneratorFree ToolDraw rectangles with an area of 24 squares, like 2 by 12, 3 by 8 and 4 by 6, and list each perimeter: 28, 22 and 20 units.1 cm squaresOne pagePrint
Make Graph Paper
Word Problem GeneratorFree ToolRooms, rugs and gardens with one side missing, so students run the area and perimeter formulas backward.Area and perimeterGrade 4
Make Word Problems

Quick Check

  1. A rectangle is 12 cm long and 7 cm wide. Find its area and perimeter.
  2. A rectangular patio has an area of 54 square meters and a width of 6 meters. How long is it?
  3. A square garden has a perimeter of 36 feet. How long is each side, and what is its area?

4.MD.3: Other Names

4.MD.34.MD.A.3CCSS.MATH.CONTENT.4.MD.A.3

Common Core State Standards © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved. Official wording from the Common Core State Standards PDFs at corestandards.org, last checked October 14, 2026. The explanation, I can statements, example, mistakes and practice on this page are EMStudio’s own, written beside the official wording. They are not part of the standard.