How to measure for shades

A great fit starts with a few careful measurements. Follow these steps to measure for inside-mount or outside-mount shades.

Before you start

  • Use a steel tape measure and keep it straight and level.
  • Measure every window separately, even if the windows look the same size.
  • Use the same unit throughout: inches or centimeters.
  • Write down all six measurements and label each window. Always record width × height.

1. Measure the window opening

Start with the opening measurements for either mount type. Measure between the inside edges of the opening, rather than measuring only the glass or an old shade.

Measure the width in three places

Measure straight across the opening from the left inside edge to the right inside edge:

  1. W1: At the top.
  2. W2: At the middle.
  3. W3: At the bottom.

Three horizontal arrows show where to measure the window opening: W1 at the top, W2 in the middle, and W3 at the bottom.

Measure the height in three places

Measure straight down from the top inside edge to the bottom of the opening:

  1. H1: On the left.
  2. H2: In the center.
  3. H3: On the right.

If there is a window sill, measure to the top surface of the sill.

Three vertical arrows show where to measure height: H1 on the left, H2 in the center, and H3 on the right. All arrows end at the top of the window sill.

2. Inside-mount shades

An inside-mount shade fits within the window recess. Check that the recess has enough mounting depth for your chosen shade and that handles or other obstructions will not interfere.

  • Order width: Use the smallest of your three width measurements.
  • Order height: Use the shortest of your three height measurements.
  • When it is close, round down. If a measurement falls between the available order sizes, choose the next smaller size.

Example: If the available sizes are in ⅛″ increments and you measure 36 3/16″, choose 36 1/8″.

Round down only as needed to the next available size. Do not subtract an extra fitting allowance unless the product instructions request one.

3. Outside-mount shades

An outside-mount shade sits in front of the opening. Use the widest width and tallest height from your six measurements, then add extra coverage.

Add 10 cm (3⅞″) to the width and 10 cm (3⅞″) to the height. This is the total extra for each dimension, not the amount to add on each side.

  • Order width: Widest opening width + 10 cm (3⅞″).
  • Order height: Tallest opening height + 10 cm (3⅞″).

Use one unit throughout: add 10 cm when measuring in centimeters, or 3⅞″ when measuring in inches.

When there is no projecting sill

Center the shade over the opening. Split the extra width equally between the left and right sides, and the extra height equally above and below the opening. In centimeters, that gives 5 cm on each side, 5 cm above, and 5 cm below.

The dashed shade outline extends 5 centimeters beyond the left, right, top, and bottom of the opening. Final width and height each include 10 centimeters of extra coverage.

When the shade finishes at a window sill

Measure the opening down to the top of the sill. Put the full extra 10 cm (3⅞″) above the opening, so the shade finishes at the sill. Split the extra width equally between the two sides.

The shade ends at the top of the projecting sill, with all 10 centimeters of extra height above the opening.

Check the space above your window. There must be enough room for the extra coverage and the shade’s mounting hardware. If you already measured from the final mounting position to the sill, that height includes the allowance. Do not add it twice.

Before you order

  • Check that you recorded three widths and three heights for each window.
  • Confirm whether you are ordering an inside mount or outside mount.
  • Check the sill, handles, and available mounting space.
  • Double-check your units and enter the final size as width × height.

Need help? Send your measurements and a photo of the window to support@coverlyshutters.com before you order.