How to measure a window for replacement, and how close is close enough

First: nail flange or reno flange?

Every replacement window is one of two things.

• Nail flange is the full-frame job. The old window comes out to the rough opening, the siding or stucco around it is cut back, and the new window is nailed to the sheathing through a flange around its edge, the same way a window goes into a new house. This is the answer for original aluminum windows, for frames that are rotten or leaking, and for any house being re-sided.
• Reno flange (also called retrofit or insert) is the window that goes inside your existing frame. The old sash and glass come out, the old frame stays, and the new window slides in with a wider flange that covers the old frame on the outside. Less disruption, less cost, and right for vinyl or wood frames that are still sound.

Not sure which you need? Aluminum, rot, leaks or sweating frames usually mean nail flange. Sound vinyl or wood usually means reno flange. If you still cannot tell, measure the nail flange way below and say so in the message. Which one is right is confirmed at the free measure, and the retrofit vs full-frame page goes into the trade-offs.

Measuring for a nail flange window

1. Go outside. This one is best measured from the outside, and it is worth a step ladder for the high ones.
2. Find the edge of the frame, not the trim. Look for the outermost edge of the window frame itself, the metal, vinyl or wood that the glass sits in. The trim boards or J-channel around it are not the window. Put the tape on the outermost edge of the frame you can get at on one side and read it at the same edge on the other.
3. Then the height, outermost frame edge at the top to outermost frame edge at the bottom. One measurement each way is enough; the final measure catches anything out of square.

Measuring for a reno flange window

1. Stay inside. This one is measured from inside the house, no ladder needed.
2. Measure inside your interior trim. Put the tape on the inside edge of the trim on the left and read it at the inside edge on the right. That is the width. Then the inside edge of the trim at the top to the inside edge at the sill. That is the height. That is close enough; the new window sits inside the existing frame and we size it exactly at the measure.

Write it down: width by height, nearest inch

Each window is width by height in inches, rounded to the nearest inch: 60 x 48, not 48 x 60. Width goes first, in the window trade and on our estimator. You do not need sixteenths. Those get measured on the day of the free measure, and nothing is ordered from your numbers.

Name the type

The type matters more to the price than an inch of size does, so take a second with this one.

• Slider. One half slides sideways past the other. The most common window on mid-Island houses from the 1970s to the 2000s.
• Casement. Hinged at the side and cranks open outward, like a door.
• Awning. Hinged at the top and cranks open outward from the bottom. Common over kitchen sinks and in bathrooms.
• Picture. Does not open at all. Often the big one in the living room, with sliders or casements either side.
• Single or double hung. The bottom half, or both halves, slide up and down. Less common here than back east.
• Bay or bow. Three or more windows joined at angles that stick out from the wall. Measure the whole assembly, outer edge to outer edge, and note how many sections.

A window with two kinds in one frame, say a picture window with a slider under it, is one unit. Measure the whole thing and describe the combination.

Count the panes and note the frame

Look at the edge of the glass where it meets the frame. One sheet of glass is single pane. Two sheets with a metal or grey spacer between them is double. Three sheets is triple. Almost everything from the mid-1980s on is double.

Then the frame: aluminum (cold to the touch, usually silver or bronze, often sweating in winter), vinyl (white or beige plastic, the standard since the 1990s) or wood (painted or stained). The frame material is the biggest clue to nail flange or reno flange.

Take six photos

One of each side of the house from the street or the yard, so every window is in a picture. Then one window up close from inside and the same one up close from outside, showing the frame, the trim and the sill. The photos tell us the frame type, how the window was installed and the condition of the sill, which is most of what the estimate depends on. Phone photos in daylight are fine.

Common mistakes, so you can skip them

• Measuring the outside trim. The trim boards outside are not the window. Nail flange: outermost edge of the frame. Reno flange: inside your interior trim.
• Measuring the glass only. The glass is the smallest part of the unit.
• Measuring the screen. The screen is smaller than the window.
• Height first. Width by height, always. A 36 x 60 and a 60 x 36 are very different windows.
• Guessing the type. If you are not sure whether it cranks or slides, try it, or send the inside photo and say so.

How close is close enough

Within an inch. The estimator prices each window to the size and type you give it, and the price moves with type, glass and count far more than with an inch of width. If the type is right and the measurements are close, the price will be close too. The free measure is where everything gets exact: every opening measured in several places, the squareness checked, the sill, the frame depth and what is behind the trim. None of that is your job.

When you have your list, the online estimator takes it, one window per row, and you will have a price for your list within one business day. If you would rather skip the tape altogether, book the free measure and we bring ours.