How to Sew a Pinwheel Mosaic Quilt Block (Free Pattern)!

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Learn to sew the beautiful Pinwheel Mosaic Quilt Block! This block takes the classic pinwheel quilt motif and wraps it up like a yummy apple pie.

I can hardly believe it, but we have finally reached the last quilt block pattern in our Kitchen Sink Quiltalong. If you have been sewing along with us this year and making quilt blocks each month, then you can sew up the last four quilt blocks now! If not, don’t worry! You can get started any time. The Kitchen Sink Quiltalong main post shares links to all the block patterns. Next month (November), I’ll share tips for sewing your quilt blocks together and I’ll show you my finished Kitchen Sink Quilt.

Here’s a sneek peek. It’s so beautiful!

The Pinwheel Mosaic block may look tricky, but it’s very simple to sew together working step by step. It starts with 4 easy half square triangles using a technique that you have probably mastered by now.

The quilt block instructions below are for sewing one block. If you are sewing the Kitchen Sink Quilt with us, you will need to make 4 Pinwheel Mosaic blocks. The free PDF that you can get by entering your email address below includes cutting information and instructions for making 4 blocks.

Download the PINWHEEL MOSAIC block pattern as a free printable PDF file.

Enter your email address below to download the free nine-patch quilt block pattern (which is pages 17-19 of the Kitchen Sink Quiltalong Quilt Pattern).

Then check your inbox for a link to download the free PDF file. It may take 5-10 minutes to arrive. If you do not see the email with a download link in your main inbox, please check your junk folder in case it went there.

By entering your email address you are signing up for my SewCanShe newsletter. That way you won’t miss any of our block patterns! If you already read my newsletter – thanks so much! You will still receive an email with a link to download the file.

Instructions for a 12” (finished size) Pinwheel Mosaic Quilt Block

These instructions make one Pinwheel Mosaic Quilt Block. Finished block size: 12’’ x 12’’ (it is 12 1/2’’ x 12 1/2’’ before you sew it in a quilt).

You will need:

  • 4 different colors or prints of fabric to cut the strips listed below (I used one light fabrics, two dark fabrics, and one medium value fabric)
  • a rotary cutter acrylic ruler, and mat
  • sewing machine
  • thread (I suggest thread matching the light or medium value fabrics)
  • ironing board and iron


Light Gray (or other light fabric):

  • cut 2 squares 4” x 4”
  • cut 4 squares 3 1/2” x 3 1/2”

Deep Coral (or other dark fabric):

  • cut 2 squares 4” x 4”

Navy (or other dark fabric):

  • cut 2 squares 5 1/2” x 5 1/2”

Coral (or other medium value fabric)

  • cut 2 squares 7 1/4” x 7 1/4”

Variation: If you want to make more than just one block, sign up above to get the free PDF file that goes with our Kitchen Sink Quiltalong quilt. It includes cutting instructions and a tutorial for making 4 blocks.

Quilt Block Assembly:

Use a 1/4’’ seam allowance and a medium stitch length such as 2.

First Make 4 HST (half square triangle) units

how to sew a half square triangle

1. Place one 4” x 4” light gray square and one deep coral square right sides together. Use a pencil or fabric pen to draw a diagonal line across the light gray square. This is a cutting line. Pin the squares together.

2. Sew 1/4’’ away from the cutting line on on both sides of the line. 

3. Cut the piece in half diagonally along the line.

Open and press the two HST units. Trim each HST to 3 1/2’’.  Repeat to make two more HST units for a total of 4 (for each block).

4. Arrange 4 HST units together in a pinwheel configuration. Sew together in 2 rows. Sew the rows together to make a pinwheel unit.

Add More Pieces around the Pinwheel Center

1. Cut the navy squares in half diagonally.

2. Center the long edge of a navy triangle along one side of a pinwheel unit and stitch. Repeat with the another triangle on the opposite side.

2. Press the seams away from the center and trim away the corners that hang off the edge.

3. Repeat to sew two more navy triangles to the top and bottom edges of the pinwheel unit. Press the seams away from the center again. Trim and square up the block so that the outer points of the pinwheel are 1/4’’ from the edge of the block (it should be a 9’’ square).

4. Cut the coral triangles in half diagonally. Sew the triangles to the sides of the 9’’ square in the same way. This time trim the block to 12 1/2’’ square.

Tip: I have used my 12 1/2” square ruler to square up every block in this quiltalong quilt so far and I love it!

5. Draw a diagonal line across the wrong side of the remaining 3 1/2’’ light gray squares. This is a stitching line.

6. Place a light gray square on the corner of the block (right sides together) as seen above. Stitch across the drawn line.

Trim away the fabric 1/4’’ past the line of stitching.

Open the corner and press. This is a ‘snowball corner.’

7. Sew snowball corners on the other three corners of the block to make a Pinwheel Mosaic Block.

If you are sewing our Kitchen Sink Quilt, you’ll need 4 Pinwheel Mosaic Blocks.

This is Block #9 in our Kitchen Sink Quiltalong

Get ready to sew all your favorite quilt blocks this year! This is the year that we are going to sew everything but the kitchen sink in our Kitchen Sink 2022 Quiltalong.

This bold graphic quilt is perfect for learning new quilt making skills that build on one another, or for putting skills you already have into a big beautiful quilt.

Tips: As you work block by block on your kitchen sink quilt, save your scraps because you will be able to use them later on.

These awesome scrapbooking bins are perfect for keeping your finished blocks safe until it’s time to sew them together into a quilt top.

Here are the 10 free quilt block patterns in the Kitchen Sink Quiltalong:

Don’t miss all my other free quilt patterns, too!


Disclosure: some of my posts contain affiliate links. If you purchase something through one of those links I may receive a small commission, so thank you for supporting SewCanShe when you shop! All of the opinions are my own and I only suggest products that I actually use. 🙂