Grade 3 · Math · Measurement

3rd Grade Perimeter Missing Side worksheets

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Perimeter Missing Side

Grade 3 Math Worksheet

NameDate

Write the answer on the line, or circle the answer.

The perimeter is 35 m. Three sides are 10 m, 5 m and 5 m. How long is the missing side, in m?
2.
The perimeter is 44 inches. Three sides are 8 inches, 15 inches and 8 inches. Which expression finds the missing side?
- 44 + (8 + 15 + 8)
- 44 - 8
- 8 + 15 + 8
- 44 - (8 + 15 + 8)
Mia uses 46 cm of ribbon to go all the way around a paper shape she cut out. Three sides are 13 cm, 8 cm and 8 cm. How long is the fourth side, in cm?
The perimeter is 27 cm. Three sides are 6 cm, 8 cm and 6 cm. How long is the missing side, in cm?
A rectangle has a perimeter of 40 m. Each long side is 11 m. How long is each short side, in m?
6.
The perimeter is 23 inches. Three sides are 4 inches, 8 inches and 4 inches. Which expression finds the missing side?
- 23 - (4 + 8 + 4)
- 23 + (4 + 8 + 4)
- 4 + 8 + 4
- 23 - 4
The perimeter is 35 feet. Three sides are 11 feet, 6 feet and 6 feet. How long is the missing side, in feet?
The class needs 34 feet of border paper to go all the way around the reading corner. Three sides are 5 feet, 14 feet and 5 feet. How long is the fourth side, in feet?
A rectangle has a perimeter of 44 m. Each long side is 13 m. How long is each short side, in m?
10.
The perimeter is 31 inches. Three sides are 5 inches, 12 inches and 5 inches. Which expression finds the missing side?
- 31 + (5 + 12 + 5)
- 31 - (5 + 12 + 5)
- 31 - 5
- 5 + 12 + 5

3rd Grade Perimeter Missing Side worksheet 1 – printable PDF — Download PDF: 1 2 3 4 5 6

About this worksheet

Perimeter Missing Side gives grade 3 students a focused page for a skill that parents and teachers often need as its own printable worksheet. Missing-side perimeter problems are a frequent assessment format beyond simply adding all sides. Students need to understand perimeter as the sum of all side lengths. The items rotate through several question types so the page is not just the same prompt with different numbers or words. Students use known sides and total perimeter to find an unknown side.

Support versions keep the reading load, numbers, or choices friendlier while preserving the same thinking. Standard versions match everyday classroom practice. Challenge versions add a closer distractor, an extra reasoning step, or less familiar examples. Before answering, students should say what the question is asking, point to the evidence, and check that the answer fits the exact skill named in the title.

What your child will learn

Use perimeter totals
Find an unknown side
Add known sides first

Common Core standard: 3.MD.D.8

Worked example

If the perimeter is 20 and three sides are 5, 4, and 6, the missing side is 5.

Common mistake

Subtracting only one side instead of all known side lengths.

Helpful hint

Add the known sides, then subtract from the perimeter.

Questions parents ask

What is the most common mistake with perimeter missing side?

Subtracting only one side instead of all known side lengths.

How can I help my child with perimeter missing side?

Add the known sides, then subtract from the perimeter.

Are these 3rd grade math worksheets free to print?

Yes. All 6 printable versions on this page are free to download and print, with no account needed.

More 3rd grade measurement

See all measurement

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