Want a rough estimate before anyone visits? Measure your windows and doors with this short guide and send us the figures with a few photos. It takes about five minutes per window.
Your measurements are for an estimate only. Before anything is ordered, our surveyor always measures every opening again with professional equipment. Never work at height or lean out of upstairs windows to measure – measure upstairs windows from inside only.
What you need:
Steel tape measure (metric)
Pen and paper
Phone camera
A helper for wide openings
Six simple rules
Measure in millimetres
Use a steel tape measure and write every figure in millimetres (for example 1,215 mm, not 121.5 cm or 4 ft). It avoids mistakes when we read your notes.
Three widths, three heights
Measure the width at the top, middle and bottom, and the height on the left, in the centre and on the right. Old openings are rarely perfectly square, so the three figures are often different.
Write all of them down
Send us every figure, not only the smallest one. The differences tell us how out of square the opening is.
Inside and outside
Where you can do so safely, measure the opening from inside and from outside. The two are usually different, because of the brick reveal outside and the plaster and linings inside.
Do not deduct anything
Do not take anything off for fitting gaps. Give us the actual opening and we will work out the frame size.
Take photos
Take one photo of each window from outside and one from inside, ideally with the tape measure visible. Photos help us more than you might think.
Where to measure: inside and outside
Inside and outside: measure the opening in millimetres, 3 widths and 3 heights. Illustration
1. Three widths and three heights. Measure the opening at the top, middle and bottom (W1–W3) and on the left, in the centre and on the right (H1–H3). Send us all six figures.2. Outside and inside heights. Outside, from the top of the sill to the underside of the arch or lintel. Inside, from the window board to the top of the opening. For doors, measure from the finished floor.
Swipe sideways to see the whole drawing →
3. Seen from above. On many London homes the window frame sits behind the brickwork. From outside you only see the opening between the brick nibs, so “brick to brick” is narrower than “reveal to reveal” inside. Please send us both.
Outside
Width between the brick reveals (brick to brick).
Height from the top of the sill to the underside of the arch or lintel.
Only from the ground floor or where you can reach safely.
Inside
Width between the plaster reveals or timber linings.
Height from the window board (or floor, for doors) to the head.
Note anything in the way: radiators, shutters, blinds, alarm sensors.
Traditional sliding sash windows in period homes. The sash boxes usually sit behind the brickwork, so you cannot see the full frame from outside.
Outside: width between the brick reveals, at the top, middle and bottom.
Outside: height from the top of the stone or timber sill to the underside of the brick arch or lintel.
Inside: width between the internal linings (the timber boards either side of the sashes), and height from the window board to the head lining.
Tell us whether the window has horns, glazing bars or a stained-glass top light, and whether the sill is stone or timber.
Casement windows (timber, uPVC, aluminium)
Side-hung or top-hung windows. The frame is usually visible from outside, either set back in the reveal or close to the face of the brickwork.
Outside: width and height of the brick opening, and if visible the frame edge to edge.
Inside: width between the plaster reveals and height from the window board to the head.
Note how far the frame is set back from the face of the wall (the reveal depth).
Count the opening panes and note which side they are hinged on.
Bay and bow windows
Bays are made up of several windows at angles to each other. Each part must be measured separately.
Measure each window in the bay separately, as for a sash or casement window.
Measure the overall length of the bay along the inside window board.
Note whether the bay is square, angled or curved; if angled, the angle between sections matters.
Bays are best measured by our surveyor – we check angles and level with professional tools before ordering.
French, patio and bi-folding doors
Large glazed doors to the garden. Floor levels and thresholds are as important as width and height.
Width of the opening between the reveals, at the top, middle and bottom.
Height from the finished floor inside to the underside of the lintel or head, on the left, centre and right.
Note the step down to the patio or garden outside, and the floor finish inside (tiles, wood, carpet).
Tell us how many panels you would like and which way they should open.
Front and back doors
Single entrance doors, often with side panels or a fanlight above.
Width between the reveals or the existing frame, at the top, middle and bottom.
Height from the top of the step or threshold to the head, on the left, centre and right.
Measure any side panels and the fanlight above the door separately.
Tell us which side the door is hinged on and whether it opens inwards or outwards.
Roof windows (VELUX and skylights)
For a like-for-like replacement, the code on the window is more useful than a tape measure.
Open the window and look for the data plate at the top of the frame. Send us a photo of it; the size code (for example MK04 or CK02) tells us the exact size.
If there is no plate, measure the outside of the frame (width and height) from inside the room.
Do not go onto the roof to measure.
Send us your measurements
Write the figures for each window or door in the form below, add photos from inside and outside, and we will reply with an estimate.
