This guide shows you how to accurately measure for replacement windows. This guide is only applicable to cords & weights timber sash window, and should not be used for spring/spiral or non-timber windows. If you want to quickly take estimated measurements for the purpose of getting a quote from Sashed then follow this guide.

Measuring a sliding sash window correctly is actually quite straightforward, but please remember the old builder’s maxim ‘measure twice, cut once’. This step by step guide to measuring for new sash windows is good are for both profile 145 and profile 150, please contact us directly for steps to measure for profile 165 and profile 190.

Step 1: Measure the depth of the existing sash box. Measuring from the outside to the inside (see picture above).

Step 2: Measure the width of the outside opening in three places; at the bottom, middle and top of the opening, the measurements should be the same but if they are notably different then check to see if there is a visible reason why; this could be because one or more bricks are uneven and the majority of the opening is the same width. You should use the measurement which is most likely to be the original outside width. If unsure, then use the measurement from the narrowest point.

Step 3: Measure the height of the outside opening in three places; at the left and right side of the opening. If your measurements differ significantly check to see if there is visible uneven bricks or slight subsidence. You should use the measurement which is most likely to be the original outside opening height. If unsure, then use the measurement from the narrowest point.

Step 4: The frame width of our sash window profile 145 and 150 is 100mm at the and top, typically a sash box should ‘face’ or show 20mm at the top with the remainder of the box hidden behind the reveal. Take the measured outside opening height taken in step 3 and add 80mm, this is the exact height of your new sash box/window.

Some original recesses were built quite tight at the top, or the lintel may have ‘bowed’ over time, so adding 80mm could mean the sash box will not fit in the recess at the top. So make adjustments where necessary and if in doubt then add just 60mm to the outside height.

For example if your outside height measurement is 1920mm, add 80mm to get 2000mm; this is the height of the sash box (window) to order.

Step 5: The frame width of our sash window profile 145 and 150 is also 100mm at the and sides, and like the top, the sides of a sash box should also ‘face’ (show) 20mm at either side with the remainder of the box hidden behind the reveal.

To calculate the width add 160mm to the outside opening width measurement taken in step 2, this is the exact width of your sash box (window).

For example if the outside width measurement is 1040mm, add 160mm to get 1200mm; this is the width of the sash box (window) to order.

Casement windows and doors are very simple to measure. There are usually no sash recesses for casement windows. Casement windows are fitted from the outside of a building, the inside opening will usually be a little smaller due to plaster build up.

Step 1: Measure the width in three places brickwork to brickwork from the outside opening.

Step 2: Measure the height in three places brickwork to brickwork from the outside opening.

Step 3: Now take the smallest measurement of the three widths and heights and take off 10mm. This is the correct size you need to order. Any small gaps or spaces can be filled in with expanding foam, silicone, and pointing.

NOTE: If a width or height is more than 1800mm, then you should add 15mm instead of 10mm.