Window counter for double glazing quotes

How to count windows for a double glazing quote

Count each opening in the wall once, room by room and floor by floor, and count a bay as one window. That is the rule our quote form uses.

1. Start on the ground floor, go room by room, then do each floor above.
2. Count each window frame once, whether it has one opening pane or three.
3. Count a bay as one window, and note its shape and how many sections it has.
4. Count French, patio, bifold, back and front doors apart from the windows.
5. Leave out any window you are keeping, and write down which one.

The windows people miss sit on the landing, on the stairs, in the bathroom, and in any porch, loft room or extension. Give every installer the same list, so each one prices the same job: our guide on how to compare double glazing quotes shows how to line the quotes up.

Does a bay window count as one window?

A bay counts as one window on our form, and you note its shape and how many sections it has. A bay is built from several units, so ask every installer to quote the bay as its own line.

Bays come in three main shapes: square or box bays, angled (canted) bays with a flat front and angled sides, and curved bow windows. Ask the surveyor to say in writing whether your bay is load-bearing. Working that out is part of the national occupational standard for surveying and fitting windows.

How many windows does a house have?

No official figure exists: government housing surveys record whether homes are double glazed, not how many windows they have. The English Housing Survey found 89% of homes in England had full double glazing in 2024 to 2025, up from 81% in 2014, and it does not count windows.

Energy performance certificates do not count them either. The method behind them estimates a home's window area from its type, age and floor area. Two homes of the same type differ by extensions, bays, loft rooms and porches, so the window counter adds up only the windows you enter.

Who measures windows for a double glazing quote?

The installer measures every opening at the survey, so a window count is enough to ask for quotes. Which? says a surveyor measures every opening, often in several places, so the new frames are made to fit the real opening.

The salesperson takes rough sizes to price the job, and the technical survey after you order takes the exact measurements. If you sign at home, you usually have at least 14 days to cancel, but made-to-measure windows can be an exception, so check the contract before you sign: see the double glazing cooling off period.

What to tell installers when they call

Read them your summary: the property type, how many windows to replace on each floor, the style of each, any bays and doors, and when you want them fitted. FENSA tells homeowners to describe the products and the timeline they have in mind.

Your summary also adds the questions that apply to your windows, from these four:

• Escape windows upstairs: a replacement window gives at least the same potential for escape as the window it replaces.
• Safety glass: glass in doors, glass beside doors and glass within 800 mm of the floor are critical locations.
• Trickle vents: new vents are no smaller than the vents in your current windows.
• Bays: whether the bay carries the wall or roof above it.

Mention blinds, shutters, alarm sensors and anything below an upstairs window, such as a conservatory roof. Which? lists restricted access, alarm sensors, blinds and shutters as things the surveyor flags before fitting. For questions about the company itself, use our list of questions to ask a double glazing salesman.