DIY Window Trim

It’s really surprising to me what a difference window trim makes in the overall appearance of my home.  About two years ago I refinished my son’s bedroom.  There is only one window in his room so I figured trimming it out wouldn’t be too much work.  Since then, I have almost finished all of the windows in my home.  With 9 foot ceilings, the windows add so much character and architectural detail.  Trimming them out draws the eye up and makes the rooms feel larger.  Enjoy the before and after pictures; the tutorial is below them.

Before and after DIY window trim in living room.
DIY Farmhouse Window Trim Process
Kitchen Window Trim

The half round portion of this window is cut from MDF with a jigsaw.

Half Round Window Trim

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  • Crown Molding
  • Half Round
  • Stool
  • Top Casing 1X6 Common Board
  • Side Casing 1X4 Common Board
  • Apron 1X4 Common Board
  • 3/4″ MDF if you are cutting out a half round window.  You will need to make a pattern from cardboard for this to trace onto the MDF.  Then cut with jigsaw and sand edges.


  1. Using a utility knife, cut the caulk along the edge of the old apron and stool.  Next, slide a thin putty knife along the cut line to ensure the caulk is completely cut.
  2. Using a pry bar remove the apron. Tip: place a thin piece of wood or the putty knife below the pry bar to prevent damage to the drywall.
  3. Using a pry bar remove the old stool.


  1. Transfer the measurements from the old stool to the new one.  Find the center of the old stool and mark a line.  Next, measure the opening of the window, then add 7″ for the side boards (3.5″ each), add 1/2″ (the two 1/4″ reveals), and 2″ (the two 1″ horns).  Basically add the measurement of the window width plus 9 1/2 inches.  Cut your new stool this length.  Find the center of the new stool and mark a line.  Put the old stool on top of the new stool lining up the center lines and trace the horn measurement on each side of the new stool.  Double check your pencil measurements up against the window opening and then cut out the side notches with your Jig Saw.
  2. Dry fit the new stool into the window opening.  Make any adjustments, check for level, and nail the stool in place.


  1. Measure the distance from the stool to the top of the window and add 1/4″ for the top reveal.  Using your miter saw cut the side casing and nail in place. Tip: Don’t forget to add a 1/4″ reveal on the inside edge.
  2. Repeat for the other side.


  1. Measure the distance from the outer edges of the side casings and cut the 1X6 to size.  Nail into place.


  1. Cut your crown molding upside down at a 45 degree angle.  I always cut the left side first.  Lay your tape measure along the bottom edge of the crown and mark the measurement for the right side.  Then move the miter saw to a 45 degree angle on the right side of the saw and make your right miter cut.  Then make a left and right cut for your returns, measure 3/4″ (thickness of common board) from the short side of the crown and cut a strait line.
  2. Measure 1/2″ from the top of your Top Casing and mark a line using a level.  Using the line as a guide attach the crown molding to the Top Casing.
  3. Using a hot glue gun, place your returns on the ends of the Crown Molding.


  1. Cut your half round molding at a 45 degree angle on the left side.  Using the length of your Top Casing, mark your length with a pencil.  Then flip the half round over and cut the other side.
  2. Secure the half round to the bottom of the Top Casing just covering the joint of the Side Casing.
  3. Cut your left return at a 45 degree angle.  Measure 3/4″ (thickness of common board) and cut a strait line for against the wall.  Repeat for the other Half Round return.
  4. Using a hot glue gun, place your returns on the ends of the Half Round.


  1. Measure from the outside of the left Side Casing to the outside of the right Side Casing.
  2. Cut your Apron to this measurement.
  3. Checking for alignment install your Apron.
  4. If you plan to install hooks on the Apron, you will need to attach the apron to the wall studs with 2 1/2″ wood screws.  Countersink the screw heads and fill with wood filler.


  1. Use wood filler to fill any knots and nail holes.
  2. Sand all the common boards smooth.
  3. Wipe all the boards down.
  4. Caulk any gaps.


  1. Using a Paint and Primer in one, apply two coats of paint.  I used Behr, Snowy Pine.  If you have a lot of knots in your boards, you can use Zinsser Cover Stain Primer first and then paint.
  2. If you do not have a steady hand, you may want to use masking tape where the casings meet the wall.  Tip: I always paint over the caulk to prevent it from yellowing and gathering dust.
  3. A good paint brush makes the job easier.  I use Purdy brushes.

This project was well worth the time and effort I put into it.  I will enjoy the beauty of these windows for years to come!


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Before and after DIY window trim in living room.

I hope this DIY window trim helps you out!



  1. Thank you SO much for writing such a detailed, helpful guide. I’m currently renting but adding window trim is on my “must do” list when I buy a place – it adds so much character! I’m bookmarking this for the future 🙂

  2. Did you trim the half circle window with the blue wall? I really want my husband to do this to our window which ic 60w by 27.5 high. We do not know where to begin. Any thoughts?

    1. Hi Paige. The large half round was cut from 3/4″ MDF. I’ve recently replaced the trim over my front door, which has a small half round. We used flexible molding and it was much easier. We have another large half round in the back of our house that I will be re-doing within the month. When it’s done, I will write a blog post on it. The MDF is cheaper, but it’s very difficult to get a smooth cut with a jigsaw. Even after I sanded it, there are still a few uneven areas. MDF is also very heavy. We chose a flexible molding that was 3/4″ thick and matched the profile of the 1X4 pine boards. It worked out great. To secure the flexible molding we used liquid nails and a brad nailer. We are in the last push of a very big renovation and I’m hoping to get the molding post up soon.

    1. Hi MT. Thank you for reaching out and I’m glad you like the tutorial. I’ve actually finished all of the window and door trim in my house. Doing the job a little at a time, saved us money and made it easier to tackle. Best wishes on your project!

  3. Hi Laura, Can you tell me how deep the window sill is? You said the horn is 1″. How far does the sill extend into the room? Also 1″ from the drywall?

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