How to Measure Blinds/Drapes

At Interior Images, we want to ensure that every blind and drapery order meets your expectations. Making sure your blinds and draperies are sized properly is an important part of the process. If you are not familiar with measuring your windows to accept new blinds or drapes, follow the steps and guidelines below.

Please submit the exact sizes, as we will not make any deductions. Tolerance on width is +/- 1/8″. Tolerance on length is -1/4″ to +1/2″.

Basic Window Terminology

  • Casing – the inside “frame” of the window which supports the sliding sashes.
  • Lintel – support beams over windows and doors (commonly the top of the window opening).
  • Sill – the horizontal part of the casing at the base of the window, which may or may not project into the room.
  • Apron – the wood trim directly below the sill.
  • Trim – the moulding which surrounds the window opening.
  • Mullion – the vertical dividers between window frames in multiple windows. Also, the wood or metal strips between window panes.
  • Muntin – same as mullion except these are horizontal dividers.

Basic Window Coverings

There are two types of basic window coverings:

  1. Soft Edge refers to window coverings made from or with fabric. Examples are drapery; valances, swags and cascades; and shades.
  2. Hard Edge refers to window coverings made from metal, plastic, or wood. Examples are horizontal blinds, vertical blinds, shutters, shades, and woven woods.

Measuring Before a Treatment and Location Have Been Chosen

Since we have no way of knowing how the final order will be written, we must record all the actual measurements and have the deductions and additions done when the order is written.

Window Measurements

If all of these actual measurements are recorded, we can provide anything from a drapery to a hard window coverings and still have any measurements that may be needed to calculate the finished width and length measurements. It is important to indicate on your diagram, however, that these measurements are not cut-length measurements.

Measurement Info Sheets

  • Bay Window Measurements (PDF)
  • Casement Window Measurements (PDF)
  • Simple Window Measurements (PDF)
  • Bay Window (with spacing) Measurements (PDF)

Common Problems to Look for Before Measuring

  1. Floors and ceilings which are not parallel
  2. Windows that are not square with the floor or ceiling
  3. Wavy walls or ceilings
  4. Proper clearance between treatments so they hang properly.
  5. Obstructions which may be in the way of the drapery or other window coverings, such as window sills, window cranks, electrical outlets, air conditioners, heating outlets, floorboard heating units, door knobs, alarm systems, any fixed object which cannot be moved, window frames, windows which open into the room, electrical switches, heating ducts, cold air returns, radiators, doors which open into the room, lighting fixtures, and pictures hanging on the wall.

For accuracy in measurement, your basic tool should be a steel “pull-out” tape measure. These come in various lengths, but the 20-foot size will be sufficient for most work. Get the type with the locking feature, which is very convenient when you are measuring in a tight corner or a spot which is dimly lit. The lock will let you preserve your measurement and bring it out to a more convenient or better lighted area for reading.

As you make each measurement, write it down to prevent errors. Use the recording sheet and a scratch pad for your measurements and calculations, then enter the final figures on the specification sheet. By filling out this important form as you go along, you’ll reduce the chance of a serious error to a minimum.

IMPORTANT! Always double check your measurements!

Measuring for Horizontal Blinds

There are two types of mounts available for horizontal blinds: inside mount or outside mount.

Inside Mount

Width: Measure the smallest inside width and subtract 3/8″ for clearance.
Length: Measure the length of the window sill from the top of the opening to the bottom of the sill.

Outside Mount

We suggest a minimum of 1-1/2″ overlap on each side of the window.

Width: Supply the exact width for the blind after you have added an allowance to each side of the blind for the overlap.
Length: Use the length from the top of the headrail to the bottom of the bottomrail after you have added for overlaps.

For more information, view this PDF.

Help from our friends at Graber Blinds

Guidelines For A Perfect Fit

  1. Measure each window individually, as size variances are common.
  2. Record width first, then height (also referred to as length) to the nearest 1/8″.
  3. Measure width from left to right, height from top to bottom, using a steel tape measure. Do not use a cloth tape.

Horizontal Blinds and Shades

Horizontal blinds and shades include Cellular Shades, Pleated Shades, Natural Shades, Roman Shades, Roller Shades, Solar Shades, Wood Blinds, Faux Wood Blinds and Horizontal Blinds.

Inside Mount

Inside mount blinds and shades are installed inside the window casing. Minimum depth requirements vary by product and headrail type, or by tube size for Solar Shades. See your designer or sales associate for complete details.

  1. Measure the exact inside width of window casing from one inside edge to the other in three different places. Record the narrowest measurement.
  2. Measure the exact height in three different places from top edge of opening to top of sill. Record the longest measurement. Solar Shades should be measured at the top only.
  3. Do not take any deductions for clearance. The factory will take necessary deductions for a perfect fit.
  4. Measure the window diagonally in two places, as shown. If the diagonal dimensions are not equal, we recommend an outside mount application for optimal function and aesthetics. 

Additional Information for Measuring Solar Shades and Roller Shades

  1. On Continuous Loop inside mounts, there is up to 3/4″ light gap per side. On Cordless inside mounts, there is approximately 1″ of light gap on the right and just over 1/2″ on the left.
  2. For optimal light and glare control, outside mount is recommended, or you may add a secondary soft window treatment (drapery or curtain) to hide the light gap on an inside mount.
  3. Fabric width is 1 1/8″-1 3/8″ narrower than finished shade width of the tube and its components on Continuous Loop shades.
  4. Fabric width is 1″-1 1/4″ narrower than finished shade width of the tube and components (without valance or side covers) on Cordless shade.

Outside Mount

Outside mount blinds and shades are installed outside the window casing, covering an area larger than the window itself.

  1. Measure the exact width to be covered. Be sure the measurement overlaps the window opening by at least 1 ½” on each side (3″ total overlap) to ensure light control and privacy.
  2. For Solar Shades make sure the measurement overlaps the window opening by at least 3″ on each side (6″ total overlap) to ensure light control and privacy.
  3. See your designer or sales associate for complete details.
  4. Measure exact height to be covered, including desired overlap (typically from top edge of molding to bottom edge, or to top of sill if there is one).
  5. The factory makes NO allowances on outside mount.

Specialty Applications

  • Measurements Required for Cellular Special Shapes
  • Measurements Required for Pleated Special Shapes
  • How to Measure for Corner and Bay Windows

Measuring for Vertical Blinds

Inside Mount

Inside mount blinds are installed inside a window casing or door, or wall to wall in a room. The window casing must be at least 2-3/4″ deep for track flush mount or 3-3/4″ deep for louvers flush mount. Otherwise, an angle bracket may be necessary.

  1. Measure the exact inside width of the window casing from one inside edge to the other in three different places. Record the narrowest measurement.
  2. Measure the exact height in three different places from top edge of opening to bottom, or top edge of sill if there is one. Record the shortest measurement.
  3. Do not take any deductions for clearance. The factory will take necessary deductions for a perfect fit.

Outside Mount

  1. Outside mount blinds are installed outside the window casing, covering an area larger than the window itself.
  2. Measure the exact width of window, including frame if there is one. Add 3″ for each side (6″ total overlap) to ensure light control and privacy.
  3. Measure height of window from top edge of molding to bottom edge, or to top of sill if there is one. Add 3″ to allow for adequate mounting area above the window.
  4. If blind extends to floor (i.e. to cover patio door), measure height in three places, take the smallest measurement and deduct at least 1/2″ for clearance so the louvers don’t touch the floor.
  5. The factory makes NO allowances on outside mount.
  6. If you want the entire window uncovered when the blind is fully open, you may need to add more than 6″ to the width.