How to Measure a Door: UK Step-by-Step Instructions
Measuring a door requires absolute precision to ensure a perfect fit, preventing draughts, sticking, and other common issues. Our step-by-step guide explains exactly how to measure a door frame and take accurate measurements in metric millimetres, whether you’re fitting a new door set or replacing an existing frame. You’ll also find expert tips on managing gaps, accounting for floor coverings, and knowing when a bespoke solution is the best choice.
- Should I measure the door or the frame? When replacing a typical front door, always measure the frame rather than the existing door. Over time, doors can warp, swell, or shrink, meaning they no longer represent the true opening size. The frame provides the most accurate guide for achieving the right fit. If there’s no existing frame, use a metal tape measure to take a brick-to-brick measurement of the opening. Then, deduct the size of the frame to ensure your new door sits perfectly within the space.
- What gaps should I leave around a door? To prevent sticking or scuffing, leave small, consistent gaps around the door when taking measurements. Aim for roughly 3mm at the top and sides, and around 9mm at the bottom to allow clearance for carpets or flooring. Most modern types of doors include a small lipping (a solid timber strip around the edges) which allows a fitter to trim or plane the door slightly for an exact, smooth-fitting finish.
- What are the standard internal door sizes in the UK? If you’re learning how to measure a door and get the perfect fit, it helps to know that most UK manufacturers produce doors in a set of standard sizes.The most common internal door size is 1981 × 762 × 35 mm (approximately 6’6” × 2’6”), though slight variations can occur depending on the manufacturer. Other typical UK internal door sizes include:
- 1981 × 610 × 35 mm (6’6” × 2’0”)
- 1981 × 686 × 35 mm (6’6” × 2’3”)
- 1981 × 838 × 35 mm (6’6” × 2’9”)
- 2040 × 826 × 40 mm (metric size)
When ordering or measuring doors, remember that thickness matters. Standard internal doors are usually 35mm, but fire-rated doors (FD30) are thicker, typically around 44mm, to meet safety regulations.
Always work with the closest standard size and check what trimming options are available before placing a bespoke order, especially for a strong front door. This ensures a precise, perfect fit without compromising security or performance. Speaking of security, let Bon Accord’s advisors help you find the best front doors for security UK.
- How do I measure when there’s no frame? When there’s no frame in place, take your measurements directly from the brick-to-brick opening. Measure the width at the top, middle, and bottom, and use the smallest value. Do the same for the height on the left, centre, and right, again noting the smallest measurement. These figures will help you determine the door set size, accounting for any required allowance. A slightly oversized opening is preferable to a tight one, as installers can adjust and trim around the frame to ensure a snug, precise fit.
Request Your Free Door Quote
Simply fill in your details for your free, no obligation quotation
Measure an opening with a frame (for replacing an internal or external door)
When replacing an internal or external door, measurements are usually taken with the existing frame in place. Measuring doors from the inside of the frame ensures your new door fits neatly within the current structure. Follow these steps for accurate results:
- Measure the distance between the inside edges of the frame at the top, middle, and bottom. Record the smallest measurement as your key width.
- Measure from the top of the frame down to the floor (or threshold, if present) at several points. Again, note the smallest measurement.
- Measure the depth of the frame and the door rebate (the recess where the door sits) to ensure proper alignment.
- Confirm whether the door opens inward or outward and whether it’s left- or right-handed, so it hangs correctly.
- Finish by checking that the frame is square by measuring diagonally from corner to corner.
Door width (inside the frame)
The vertical sections of a door frame that form the sides of the opening are called jambs.
- Measure the internal width of the frame from jamb to jamb.
- Take measurements at the top, middle, and bottom of the frame.
- When recording your measurements, note the widest reading, as this will help ensure your new door fits smoothly and reduce the need for any trimming during installation.
Measuring Door Height (finished floor to underside of head)
To accurately measure the height of any replacement doors’ frame:
- Measure from the finished floor (or threshold if there is one) up to the underside of the door frame.
- Take measurements at the left side, centre, and right side of the opening.
- Use the tallest measurement as your recorded height to ensure the new door won’t scrape against the floor or threshold.
Door thickness & frame rebate
When measuring a door, it’s important to record both the door thickness and the frame rebate to ensure a perfect fit, and it’s simple to do.
- Start by locating the edge of the existing door (the part that sits within the frame when closed), and measure its thickness from one face to the other using a ruler or tape measure.
- Then, measure the rebate by noting both its width and depth.
- For a flush, secure fit that seals properly when closed, the new door’s thickness must complement the dimensions of the frame rebate.
Tools you need, preparation and the golden rules
Avoiding an ill-fitting door starts with the right tools and a little preparation. All you’ll need is a rigid metal tape measure, plus pencil and paper to note everything down.
Before you begin, clear away any obstructions and remove door stops or trims, whether you’re measuring for a sleek grey front door or any other style.
Take all measurements in millimetres for complete accuracy, noting the largest figures for width, height, and depth. Always double-check your readings to rule out any errors before placing your order.
Clearances, trimming and floor coverings
One of the most important steps when measuring a door is allowing for the right clearances around its edges.
Aim for a 3mm gap at the top and sides and around 9mm at the bottom. This ensures smooth operation and provides space for any future expansion or contraction.
Make sure the bottom clearance is sufficient so carpets or floor tiles don’t obstruct the door as it opens and closes. Always follow the manufacturer’s trimming guidelines to guarantee a precise fit and easy movement.
And while you’re at it, don’t forget to explore how to pick a front door colour to complement your home’s style.
Compare your door measurements to UK sizes (and when to order bespoke)
Once you’ve taken all your measurements, compare them against the UK’s standard internal door sizes, typically ranging from 540mm to 838mm in width, 1981mm or 2040mm in height, and 35mm to 44mm in thickness.
To determine if a standard door will fit, factor in the expected clearances: around 2-3mm at the top, 2mm on each side, and 8-10mm at the bottom for smooth movement. If these gaps can be achieved through trimming, a standard door should work perfectly.
However, if your opening sits well outside these measurements, the frame isn’t square, or a unique thickness is required, opting for a bespoke door is the most reliable solution.
If measuring a door feels a little out of your comfort zone, let the experts at Bon Accord take care of it – it’s all part of the service when you purchase one of our designs. With our many years of experience, we are well-versed in recording door measurements. Our team will visit your home to inspect the opening, take precise measurements, and ensure everything is perfectly prepared for your new door installation.
REQUEST YOUR FREE QUOTE
Simply fill in your details for your free, no obligation quotation, and click "Get Quote"
Want to speak with an Advisor? Give us a call on 01224 588944
Our friendly team will be pleased to help with any questions you may have.