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You might be surprised by the variety of sizes available when shopping for new doors. While there are some "standard" dimensions used by most suppliers, these aren't always universally applicable, especially in markets like the UK where older doors are often uniquely shaped.
Because of this, it's always wise to measure your existing doors before purchasing new ones, rather than solely relying on standard sizes, to ensure a proper fit.
To help you get accurate measurements and avoid common pitfalls, we've put together a straightforward guide.
**Table of Contents**
- How to Measure for New Internal Doors
- How to Measure for New External Doors
- How to Measure for Bifold Doors
**How to Measure for New Internal Doors**
The simplest approach is to measure the door you're replacing. But if the door doesn't fit well, there's no current door to measure, or it's a new opening without a Frame, you'll need to measure the gap and make some adjustments, as detailed below. In every scenario, you'll need to measure the width, height, and thickness of the door or opening.
**Step 1: Measure the Width**
- Use a measuring tape to measure the width at three points: the top, middle, and bottom.
- Older doors and openings may not be perfectly rectangular, so take multiple measurements and use the largest value as your door width.
- Ensure you're only measuring the door itself, excluding any extras like weatherstripping.
**Step 2: Measure the Height**
- Run the tape measure from the top of the door to the bottom in a straight line. Take measurements in various spots to account for any differences in height.
- Double-check that you're not including additional door components, such as a door sweep, in your measurements.
**Step 3: Measure the Door Thickness**
- Measure the thickness of your door by running the tape measure across the edge of one side to the other.
- Note down the number, then measure the door jamb on the frame to confirm it matches, as you may need both figures.
**Additional Considerations for Measuring Internal Doors**
**If Measuring Between the Frame:**
If your opening already has a frame installed, your measurement should be "frame-to-frame." Measure the width from left to right, then deduct 2-3mm from each side to allow for smooth operation and prevent potential warping during seasonal humidity changes.
**If There’s No Door or Frame:**
For new openings without a frame, you'll typically measure the "brick-to-brick" opening. Measure the rough opening size (both width and height) and consider adjustments for framing.
*Tip:* Once you have all three measurements, repeat the process for each door you wish to replace. Remember, not all internal doors in your home will be identical in size or thickness, so measure each one separately.
[Video: Leader Doors - How to Measure and Install a Door]
**How to Measure for a New External Door**
External doors are measured similarly to internal doors, though they may require extra considerations for the best fit.
**Measuring for a New Door in an Existing Frame**
If you're installing a new door into an existing frame, it's better to measure the new frame for a flush fit rather than the old one. Measure:
- Width
- Height
- Thickness
- Side panels (if applicable)
**Replacing the Door and Frame**
If you're replacing both the door and the frame, measure the structural opening, or "brick-to-brick."
When measuring a rough opening, remember to factor in your new frame. We suggest subtracting 2 inches from the width and about 2.5 inches from the height of the brick opening for a proper fit. You might also need to account for draft excluders, which can add up to 25mm to the height.
*Tip:* The height measurement is especially crucial for external doors to ensure effective weatherproofing.
**How to Measure for Bifold Doors**
For bifold doors, measure the full width and height of the opening, including the frame.
- Measure the width at the top, middle, and bottom, and use the smallest width for your order.
- Measure the height at various points and use the smallest measurement.
- Check the diagonal from corner to corner to confirm the opening is rectangular. The two numbers should be nearly identical.
- Precision is key for bifold doors to function smoothly, so measure accurately and ensure the floor is level for proper sliding or folding.
For larger openings, especially those with glass doors, there may be specific UK building regulations to follow, such as safety glass requirements. Always consult a professional if you're unsure.
**What If I Can’t Find the Right Door Size?**
If you're having trouble finding the exact size or aren't confident in your measurements, consider purchasing an internal door slightly larger than your opening to trim it down. For external doors, use the smallest measurements possible.
The threshold for adjusting doors varies by manufacturer, so check this before buying. We've also created a guide on standard door sizes to help you choose correctly.
**Can I Just Measure the Door I’m Replacing?**
While replacing a door, measuring the existing one is the easiest method. However, it's advisable to verify that the door fits snugly in the frame and doesn't rub against the frame or leave large gaps around the edges.
**Shop Internal and External Doors from Leader Doors**
With your measurements in hand, you can begin searching for the perfect door for your space. At Leader Doors, we offer a broad selection of internal and external doors, along with door frames, tailored to meet your needs. We even provide bespoke doors crafted according to your specifications.
Contact our friendly Door Experts in the sales team for further assistance. They can help determine the right size, discuss pricing, and check availability over the phone.
**Related Articles**
- How to Trim Engineered Timber Doors
- How to Fit a Door Frame
- How To Fix A Sticking Door
This guide should help you confidently measure and select the right doors for your home.