How To Measure
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How to measure your window
Getting accurate measurements is the most important step when ordering replacement windows online. Follow these five steps and record all measurements in millimetres (mm).
Before you order
Check all measurements carefully. If you are unsure, send us your measurements, a simple sketch and a few photos.
Our team will check everything free of charge before you place your order.
What you will need
- Tape measure
- Pen or pencil
- Paper or a measuring sheet
- A second person for larger openings
- A ladder, if needed
Step 1: Measure the width
Measure the brick-to-brick opening in three places: top, middle and bottom.
Record all three measurements and use the smallest measurement.
Do not measure from the edges of the existing window frame.
Step 2: Measure the height
Measure the height of the opening in three places: left side, centre and right side.
Measure from the underside of the top lintel down to the cill.
Record all three measurements and use the smallest measurement.
Step 3: Allow for fitting clearance
Once you have the smallest width and height, deduct a fitting allowance:
- Deduct 10 mm from the overall width.
- Deduct 10 mm from the overall height.
This creates approximately 5 mm clearance around each side.
Worked example
- Brick opening width
- 1,200 mm
- Order width
- 1,190 mm
- Brick opening height
- 1,050 mm
- Order height
- 1,040 mm
Fitting clearance illustration. Not to scale.
Step 4: Check the window cill
Look at the bottom of the window from outside.
If the window has a cill, measure the depth from the face of the frame to the outer edge.
Choose the correct cill size when ordering.
Cill sizes shown in the guide
Step 5: Check opening direction
View the window from outside. Indicate which side the hinges are on and the direction the window opens.
Left-hand or right-hand refers to the hinge position as viewed from outside.
Opening types
- Left-hand
- Hinges on the left.
- Right-hand
- Hinges on the right.
- Top-opening
- Hinges at the top.
- Side-opening
- Hinges on the side.
Measure twice, order once.
Still not sure? Send us your measurements, sketch and photos, and we will check everything for free before you order.
How to measure your door
Accurate measurements are the starting point for a replacement door that fits. Use this guide to record your opening and understand the checks needed before confirming your order size.
Before you start
This guide is for a replacement external door and frame. It is not a measuring guide for a replacement door leaf or an infill panel fitted into an existing door.
Opening dimensions are not automatically your order dimensions. Your installer should confirm the fitting allowance and how the chosen threshold, cill and frame extensions are included. If anything is unclear, contact EverFrames before ordering.
What you will need
- A rigid tape measure marked in millimetres.
- A notebook or a printed measurement record.
- A spirit level and, where practical, someone to help.
- Photos of the full entrance from inside and outside, including the bottom of the frame.
Record every dimension in millimetres (mm). Label the opening clearly if you are replacing more than one door.
1. Identify the opening you are replacing
For a complete door-and-frame replacement, identify the structural opening that the new assembly will fit into. On a typical brick-built opening, this means the space between the masonry sides and beneath the head or lintel.
Do not use the width of the moving door leaf, the gap you walk through or the distance between decorative trims as the opening measurement.
Render, plaster, trims and the existing frame can hide the true edges. If you cannot establish them confidently, ask your installer to survey the opening. Do not dismantle the existing door just to obtain a measurement.
Where the inside and outside openings differ, record both and have your installer establish the intended frame position. Recessed, stepped or irregular openings need an individual assessment.
Measure the width
Measure horizontally across the structural opening at three positions:
- Near the top.
- At the middle.
- Near the bottom.
Keep the tape straight and level. Record all three readings and identify the smallest opening width. Do not average the readings or round them up.
Measure the height
Measure vertically from the underside of the structural head to the proposed supporting base of the new door assembly at three positions:
- On the left.
- At the centre.
- On the right.
Record all three readings and identify the smallest opening height. Have your installer confirm the base level if an existing cill or threshold conceals it.
4. Check the opening and floor levels
Measure both diagonals, from corner to opposite corner, and compare them. Different readings can indicate that the opening is out of square. Check the sides for plumb and the head and base for level.
Keep the complete set of readings for your installer. The smallest width and height alone do not prove that a square frame will fit an uneven opening.
Note the finished internal floor level, any planned flooring changes, the external step and the door’s swing clearance. The selected threshold and any cill must work with these levels.
5. Account for the cill, threshold and add-ons
Agree the complete assembly with your installer before finalising the height and width:
- Threshold: the bottom section of the door frame that you step over.
- Cill: the projecting profile beneath the frame, where specified.
- Frame extensions or add-ons: profiles fitted to the top or sides where the installation requires them.
A cill described as 150 mm generally refers to its front-to-back depth, not a 150 mm addition to the door height. Use the actual profile dimensions for your chosen product.
Confirm whether the product’s “Overall Width” and “Overall Height” fields include the selected cill and add-ons. Do not add or deduct a component twice. Keep a record of the complete assembly size and any separate frame-only dimensions.
6. Agree the final order dimensions
The frame assembly needs an appropriate installation clearance within the opening. Your installer should determine the allowance using the manufacturer’s guidance and the condition and construction of the opening.
Smallest opening width − agreed total width allowance = target assembly width
Smallest opening height − agreed total height allowance = target assembly height
These are assembly dimensions. Translate them into the product’s order fields only after confirming how the selected components are included.
Do not apply a standard 5 mm or 10 mm deduction without checking it is correct for your installation. Do not assume that a fitting allowance will be deducted automatically from the dimensions you enter.
Check the permitted size range for the exact door style and configuration. If your confirmed size falls outside it, contact us rather than changing the figures simply to fit the form.
7. Confirm hinge side and opening direction
Record the proposed hinge side and swing direction separately. Use the viewing convention shown on the product page or confirmed order drawing.
- Hinged left or right: which side the hinges are on from the stated viewpoint.
- Opening in: the door swings into the property.
- Opening out: the door swings towards the exterior.
Label your sketch “viewed from outside” or “viewed from inside” so it cannot be misread. If the product page does not state the viewpoint, ask EverFrames to confirm before selecting the hinge side.
A door-style name containing “Left” or “Right” may describe its design layout. Always check the separate hinge and opening selections as well.
Your measurement record
Copy or print this table and keep it with your photographs and installer’s specification. The first six readings are opening measurements, before any fitting allowance.
| Measurement or detail | Record |
|---|---|
| Opening width: top / middle / bottom | _____ / _____ / _____ mm |
| Opening height: left / centre / right | _____ / _____ / _____ mm |
| Smallest opening width / height | _____ / _____ mm |
| Diagonal A / diagonal B | _____ / _____ mm |
| Base level, floor levels and frame position | ________________________ |
| Threshold / cill / add-ons | ________________________ |
| Agreed total width / height allowances | _____ / _____ mm |
| Final overall assembly width / height | _____ / _____ mm |
| Sizes to enter in the order fields | Width _____ mm Height _____ mm |
| Components included in those order sizes | ________________________ |
| Hinge side / opening direction / viewpoint | ________________________ |
| Checked by installer / date | ________________________ |
Final checks before you order
- All measurements have been taken twice and recorded in millimetres.
- The structural opening and intended base level have been identified.
- The installer has checked squareness, floor levels and swing clearance.
- The fitting allowance and component inclusions have been confirmed.
- The final dimensions suit the selected door’s size limits.
- The design variant, hinge side, opening direction and viewpoint agree.
- Colours, glazing, handles, locks and other accessories have been reviewed.
Common measuring questions
Can I measure the existing door leaf?
Not for a complete door-and-frame replacement. The moving leaf is smaller than the full assembly. Record the structural opening and have the final assembly dimensions checked.
Should I subtract 10 mm from my measurements?
Only if that is the allowance confirmed for your chosen product and installation. Allowances are not interchangeable between every opening, frame material or threshold arrangement.
What if I have a sidelight or a glazed panel above the door?
Record the full opening and take photographs, then contact us before ordering. The door, separate panels, coupling profiles and any transom positions need an agreed drawing and breakdown of dimensions.
Does this guide cover replacing a PVC-U door panel?
No. An infill panel fitted into an existing door requires different measurements, including panel thickness and the glazing rebate details. Ask your installer to identify the correct panel specification.
What if I am unsure about the measurements?
Ask a suitably qualified installer to survey the opening before placing an order. EverFrames can clarify product options and order fields; photographs and a general guide do not replace an accurate site survey.