How To Measure For Replacement Windows

Whether you’re replacing a broken window (oops) or upgrading, measuring for replacement window requires a few steps to get it right.

Measure width

First, take three horizontal measurements for the width. Measure the opening at the top of the window, in the middle, and at the bottom. If your window has trim, place the tape measure inside the jamb to get the correct measurement. Take the smallest of the three measurements.

Double hung windows have a parting bead which is just a wood strip that spans the window. Be sure to measure the entire width, not the parting bead or any trim strips. Also remove any jamb liners the window might have.

Replacement windows are sold in 3 ¼ inch thickness that fits in the pocket between the outside and inside stops.

Measure Height

Like the width, measure the height in three places, on either side and the middle of the window.

Place the tape measure on the sill when measuring for the height. On older double hung and single hung windows, the sill is the piece of wood that the window closes to. Usually the sill is on the outside and slopes downward so that water will drain off. On the inside, the decorative sill is called the window stool. Measure behind that.

As with the width, measure from the sill to the top of the inside jamb, not a window stop or parting bead.

Measure Depth

Next, measure the depth of the window. Again, ignore any parting strips, pulleys or stops. Measure in several places around the window.

Ordering your window

Depending on where you get your window, provide the opening size only. Most manufacturers will deduct about ¼ inch from your measurements and choose the nearest ⅛ inch measure.

This allows the window to fit in the frame without damaging the opening. Windows can be shimmed in and insulated

The window must fit in to your space and be plumb and level, even if the opening isn’t. Unless you plan to change the size of the window, most newer windows come in standard sizes. Custom size windows are also an option, just know that they cannot be returned for a different size.

Choosing your replacement window material

  • Wood – wood windows are quite beautiful, but often need the most maintenance and upkeep. Painting or waterproofing must be performed every two to three years.
  • Clad Wood – the best of both worlds, clad wood means that you will have beautiful wood windows on the inside of your house and metal on the outside. This eliminates the extra maintenance.
  • Vinyl – vinyl windows are most common. They provide excellent thermal insulation and can often reduce heating and cooling bills. Vinyl windows also require zero maintenance and cheaper than wood or clad wood options.
  • Aluminum – older cheap windows are often made of aluminum. These windows are notoriously terrible for insulation since metal is a conductor. Newer aluminum windows are insulated with vinyl to reduce heat transfer and condensation problems.
Bay windows and single hung windows

Choosing your window operator type (or window style)

  • Casement – the window is hinged on one side and can be cranked open to 90 degrees with a handle.
  • Awning – instead of being hinged on one side, the top of the window is hinged. The window is cranked out so that the bottom opens to the outside.
  • Single-hung – In a single hung window, the top sash is fixed and the bottom window can be slid upwards.
  • Double-hung – Like a single-hung window, the bottom can be slide upwards. However the top sash can also slide down. This is often a great choice when you have pets or young kids that you worry about falling out of the window.
  • Slider – a slider window, as the name suggests, one sash slides to the side on a track. Slider windows depending on the size may have one fixed side or the center may be fixed while each side may slide toward the center.
  • Picture – a picture window does not open. The fixed window maximizes views and also may be used for insurance and safety reasons.
  • Bay window – These windows are often used as focal points of a room, in the kitchen, dining, living, or even bedroom. Three windows are set at 35 or 45 degrees together and can either be fixed or operable.
  • Bow window – Similar to a bay window, a bow window is often used as a focal point of the room. However instead of three windows, a bow window can have 3, 5, 7 or 9 windows set together at a 10 degree angle.
  • Basement or Hopper window – Like an awning window, this style of window is often cranked out. It’s hinged at the bottom instead so that basement rooms can get ventilation.
  • Garden window – Often used in a kitchen, a garden window extends out and has glass on three sides and a shelf in the middle for plants. The two sides are casement windows that crank outwards and the center glass is fixed.

Window Design Details

Historically, glass could not be made in large sheets which is why older homes often have the grid look separating glass. Large sheets couldn’t be moved without breaking, thus they wedged small squares between thin wood supports, now called grilles.

This colonial look is still replicated today solely to add to the exterior style and look of the home. The traditional grid style is called “Colonial”. Different window manufacturers have different designs to choose from.

Regardless of the design, there are design considerations that can have an impact on the energy efficiency of the home.

  • Full Divided Light – in a window like this, there are actual structures (wood, vinyl, metal) that separate each piece of glass. Most windows are now double pane, so the divider extends out of each piece of glass. Some window companies have developed technology to make this window more energy efficient, but traditionally you may have heat loss (or A/C loss) with this type of window. It’s also hard to clean, since you must clean each individual square.
  • Simulated Divided Light – this window has double pane glass with a grille attached to the glass on either side to give the aesthetic look without losing heat. There is no spacer between the glass
  • Removable Interior Grille – this grille is attached to the interior window with a clip or fastener. This gives you the desired aesthetic and allows you to remove it to clean the window.
  • Between the glass grille – this style gives the homeowner the best of both worlds. There is no exterior or interior grille. Instead, the grille design is between the glass panes for easy cleaning.

Other names for this aesthetic are window mullions, divided lites, window grids, or grills.


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