How to Measure Internal Doors
How to Accurately Measure Internal Doors
Measuring internal doors correctly is essential for ensuring a perfect fit, whether replacing an existing door or installing a new one. You'll need a tape measure and a clear understanding of what to check to get started. From measuring the height and width to accounting for the door frame and thickness of the door, accuracy is key. Here we will show you how to measure the internal doors step by step, from the width and height to all other critical dimensions. Also, we outline standard sizes and door widths that will guide you in getting a fit that is just right for the space.
Gather Your Tools
Before you begin, make sure you have these tools:
- Tape measure
- Pencil and paper
- Spirit level
- Step ladder (if necessary)
- Measuring stick or straight edge
Measure the Door Height
Remove the Old Door![]()
If you are replacing an existing door, start by removing it from its frame. This will clear any obstructions to access the frame for correct and accurate measurements.
Measure the Opening
Measure the door opening height from the floor to the underside of the door frame. Take measurements at three points: left, middle and right.
Record the Smallest Measurement
Note the smallest measurement so the new door will fit into the shortest part of the opening.
Measure the Door Width
Measure the Width of the Opening
Measure the width of the door opening at three points: top, middle, and bottom.
Record the Smallest Measurement
Again, write down the smallest measurement to ensure the new door fits into the narrowest part of the frame.
Measure the Door Thickness
Check the Door Frame
Measure the thickness of the existing door frame or the door itself if you’re using the same frame.
Standard Thickness
Standard thicknesses for internal doors are generally 35mm or 40mm thick. Be sure to make your measurements one of these standard widths or make a note for a custom door if otherwise.
Measure Door Frame Depth
Frame Depth
Take the depth of the door frame to fit the new door snugly within the door frame, which also houses the rebates—the slot in the door frame in which the door sits.
Allow for Architrave
If your frame has architrave (the decorative moulding that goes around the frame), ensure that this is also included in your measurement taking if it will impact how the door fits.
Door Swing and Hardware Considerations
Door Swing
Decide on the direction of door swing – inwards or outwards, left-hand or right-hand side. That is important to get the order for the correct type door and hinges.
Hinge Position
Measure and record the positions of existing door hinges if you’re replacing a door. This ensures the new door can be hung with minimal adjustments.
Handle and Lock Position
If you’re using existing door handles and locks, measure their positions on the old door and ensure the new door can accommodate them.
Double-Check Your Measurements
Re-measure
Double-check all your measurements to ensure accuracy. Mistakes can be costly, especially if you’re ordering a custom-made door.
Cross-verify
If possible, get a second person to check your measurements to prevent any mistakes.
Choose Your Door
Standard vs. Custom
Based on your measurements, determine whether you need a standard-sized door or a custom-made one. Standard sizes are generally cheaper and more readily available.
Material & Style
Choose the material: wood, MDF, glass, etc and style: panel, flush, glazed, etc that fits.
Ordering and Installation
Order Your Door
Place your order with us, making sure that all of your measurements and specifications are clear (for custom doors, you will be able to input your sizes on the product page)
Installation
When you receive your door, start by following the manufacturer's instructions for installation. We recommend hiring a professional installer if you are not comfortable with DIY projects; the door will be hung correctly and will operate smoothly.
Follow these steps, and you will not go wrong with your new internal door; it will fit perfectly and enhance both the aesthetic and functionality of your space. The basis of any successful door installation is a precise measurement, so take your time and measure carefully.
Frequently Asked Questions
How do I know what size interior door to buy?
Measure the width of the door frame at three points: top, middle, and bottom. The widest of these measurements will give the correct door width. Note each measurement with a tape measure, keeping it from the left-hand side of the frame to the right for each. All three are noted to find the widest and hence fit perfectly.
How do you measure for an internal door?
Take a measure from the top corner of the door frame all the way down to the bottom corner on the left-hand side. Do the same in the middle of the door and then once more on the right-hand side. The longest number of these measurements will represent your required height for a door.
How to find exact interior door replacement?
Simply measure the door itself and order one in the same size. Remember that doors are typically manufactured slightly smaller than their nominal size—for example, a 29.75" door is considered a 30" one. Remember, if you’re working with a pre-hung unit, it will be about 1-1.5" wider, and the rough opening will generally need to be 2-3" larger than the door size to accommodate the frame and fittings.
What size is a standard UK internal door?
The internal door width for England and Wales is 762 mm approximately (2 feet 6 inches). In Scotland, the standard internal doors are somewhat narrower usually about 726mm in width (2 feet 4 ½ inches).
