Grade 3 · Math · Measurement

3rd Grade Perimeter Missing Side worksheets

6 printable versionsBuilding ConfidenceAbout 9 minutes eachFree · no account

When it’s done, scan the sheet with your phone and PencilGo marks it and picks the next one. Create a free account

★

Tired of searching for worksheets?

We’ll email one free Grade 3 worksheet every school day. Your child does it on paper. No account needed.

Version

Perimeter Missing Side

Grade 3 Math Worksheet - Building Confidence

NameDate

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

The perimeter is 25 cm. Three sides are 5 cm, 9 cm and 5 cm. How long is the missing side, in cm?
2.
The perimeter is 13 m. Three sides are 3 m, 2 m and 2 m. Which expression finds the missing side?
- 3 + 2 + 2
- 13 - (3 + 2 + 2)
- 13 - 3
The perimeter is 21 inches. Three sides are 4 inches, 8 inches and 4 inches. How long is the missing side, in inches?
Dad needs 27 m of fence to go all the way around the garden bed. Three sides are 7 m, 5 m and 5 m. How long is the fourth side, in m?
A rectangle has a perimeter of 18 cm. Each long side is 6 cm. How long is each short side, in cm?
6.
The perimeter is 29 m. Three sides are 8 m, 5 m and 5 m. Which expression finds the missing side?
- 29 - 8
- 29 - (8 + 5 + 5)
- 8 + 5 + 5
The perimeter is 14 inches. Three sides are 2 inches, 6 inches and 2 inches. How long is the missing side, in inches?
Mia uses 13 cm of ribbon to go all the way around a paper shape she cut out. Three sides are 3 cm, 2 cm and 2 cm. How long is the fourth side, in cm?
The perimeter is 25 cm. Three sides are 5 cm, 8 cm and 5 cm. How long is the missing side, in cm?
A rectangle has a perimeter of 12 m. Each long side is 4 m. How long is each short side, in m?

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

Every sheet you scan goes into your child’s record: dated, marked and ready for the year-end portfolio. Homeschool records