How to Measure for a New Door - A Step-by-Step Guide

Learning how to measure for a new door is all about getting those crucial frame dimensions right. Whether you’re updating an internal door or fitting a secure external entrance, accurate measurements make all the difference between a perfect fit and a frustrating installation.

Before picking up that tape measure, remember to always measure the frame, not your existing door. This is doubly important in older properties, where settling and wear can create subtle variations in frame dimensions over time.

Ready to start measuring? Let’s walk through the process step by step to ensure your new door fits perfectly.

Key Takeaways

• Always measure the frame, not the old door - take width and height measurements from three different points to account for any variations.
• For fire doors, ensure your frame depth matches the door thickness requirements - 35mm for FD30 and 54mm for FD60 doors.
• Remember to factor in floor clearances - allow 10mm for standard flooring and up to 15mm for carpeted areas.
• When measuring external doors, add extra clearance (2-3mm per side) for weatherstripping to ensure proper sealing against the elements.

Essential Preparation for Measuring a New Door

Key Tools Needed

Getting accurate measurements starts with having the right equipment at hand:

• A reliable tape measure (preferably metal)
• A spirit level
• A measuring square
• A pencil
• A notepad for recording measurements

Having these tools ready before you begin ensures you can take accurate measurements in one session, reducing the chance of recording errors or inconsistencies between measuring attempts.

Preparing the Door Frame

A clean, clear frame makes measuring much simpler. Take time to remove any old fixings, clean away debris, and ensure your frame is stable. Good lighting helps, too - use a torch if needed to see into those darker corners.

Working with a clear frame not only makes measuring easier but also helps spot any potential issues that might affect your new door’s fit.

Step-by-Step Guide to Measuring a Door for Replacement

Step 1: Measure the Width of the Door Frame

Getting your width measurements spot-on is crucial for a smooth-operating door. Start at the widest part of the frame, and don’t forget to measure in three different places - this simple step catches any frame irregularities that might cause problems later.

Begin at the top of your frame, then measure the middle, and finally check the bottom. You might notice slight variations - that’s perfectly normal, especially in older properties. When ordering your door, we always use the smallest measurement to ensure your new door won’t catch or stick.

Most internal doors in the UK typically measure around 762mm or 838mm wide but never assume. Even a few millimetres can make the difference between a perfect fit and a problematic installation.

Step 2: Measure the Height of the Door Frame

Height measurements need just as much attention as width. Take three measurements here too - one on the left side, one in the middle, and one on the right side of your frame.

Don’t forget about your flooring. If you’re measuring for a room with carpet, you’ll want to factor in extra clearance at the bottom. The last thing you need is a door that drags across your new carpet every time you open it.

Write down all your measurements clearly - mixing up numbers at this stage can lead to costly mistakes. And yes, those few millimetres really do matter.

Step 3: Check Frame Squareness with Diagonal Measurements

Here’s a step many people skip, but it’s absolutely crucial. Checking your frame’s squareness can save you numerous headaches down the line.

Measure from top left to bottom right, then from top right to bottom left. These measurements should be within 5mm of each other. If they’re not, your frame isn’t perfectly square - and that’s more common than you might think, especially in older buildings.

A frame that’s significantly out of square might need a made-to-measure door to ensure a proper fit. Better to know this now than after you’ve ordered a standard-sized door.

Step 4: Measure Door Thickness

Your frame depth determines what thickness of door you can install. This measurement is particularly crucial for fire doors and external doors.

Standard internal doors like LPD White Moulded Mayfair 4-Panel Internal Door or JB Kind Caprice Grained White Primed Internal Door usually come in at 35mm thick. External doors tend to be chunkier at 44mm, while fire doors vary - FD30 doors typically need 44mm, and FD60 doors require 54mm.

Take this measurement in several spots along your frame. Like width and height, the depth might vary, especially in older properties. Knowing these variations helps you make informed decisions about your new door.

Special Adjustments for Different Types of Doors

External Door Measurements

External doors need extra attention because they’re your home’s first line of defence against the weather. When measuring for doors like LPD Norfolk Oak External Door or Mendes Hampstead Hardwood Unglazed External Door Pair, you’ll need to think beyond basic dimensions.

The threshold area needs particular care - it’s a crucial spot where many measurements go wrong. We recommend adding 2-3mm extra clearance on each side compared to internal doors. If your threshold slopes (common in older properties) or sits unevenly, measure both the highest and lowest points. For sloping thresholds, always measure from the highest point to ensure your door will clear properly and still maintain a weather-tight seal.

Different external door materials need different considerations too. Solid oak doors might need extra clearance as they can expand slightly in humid weather. Redwood doors tend to be more stable but still benefit from that additional weatherstripping space.

Don’t forget about weatherstripping. Your measurements need to account for these essential seals that keep the British weather where it belongs - outside. A properly fitted external door should be snug enough to prevent drafts but not so tight that it sticks in damp weather.

Fire Door Measurements

Fire doors demand precision - there’s simply no room for error when safety is at stake. The frame depth requirements are non-negotiable: at least 35mm for FD30 doors and 54mm for FD60 doors.

These heavier doors need robust support. Pay special attention to hinge positions and ensure your frame can handle the extra weight. FD60 doors typically need an additional hinge compared to standard doors.

Building regulations vary depending on your door’s location within the property. Some areas require FD30 protection, while others need the extra security of FD60 - check your local requirements before ordering.

Measuring for Non-Standard Frames

Older properties often throw up interesting challenges when it comes to door-fitting. Those charming period features can mean frames that aren’t quite square or consistent in size.

Victorian and Georgian properties particularly tend to have unique dimensions. What looks like a standard door opening might have subtle variations that only become apparent when you measure carefully.

In these cases, made-to-measure doors are often your best bet. They’ll save you countless headaches while hanging the door. Plus, they help maintain your property’s character - something that’s priceless in period homes.

Avoiding Common Mistakes in Door Measurement

Top Mistakes and How to Avoid Them

Ever seen someone measure once and order in haste? We’ve witnessed plenty of costly mistakes that could have been easily avoided. Here are the typical pitfalls to watch out for.

Measuring the old door instead of the frame is probably the most common error. Your existing door might have been trimmed or could be the wrong size to begin with.

Another frequent mistake is forgetting about floor coverings. That perfectly measured door won’t seem so perfect when you realise it won’t clear your new carpet.

Frame depth often gets overlooked, too. Without this crucial measurement, you might end up with a door that’s too thick or thin for your frame - neither is ideal.

Measurement Checklist for Accuracy

Use this essential checklist before finalising your door order:

1. Width measurements at three points
2. Height measurements at three points
3. Diagonal measurements
4. Frame depth
5. Floor clearance requirements
6. Additional space for hardware

Having this checklist complete ensures you’ve gathered all the necessary measurements for your new door. Keep your measurements written down in a safe place, and consider taking photos of your measuring process for reference.

Measurement Terms Explained

Before you dive into measuring, it’s important that you understand these terms:

• Rough opening: Think of this as your frame’s raw dimensions - it’s the basic size of the hole in your wall.
• Clearance: That small but crucial gap around your door that lets it open smoothly. Usually about 2-3mm each side.
• Frame depth: How thick your frame is, measured from front to back. This determines what door thickness will work best.
• Fire rating: For fire doors, you’ll see terms like FD30 (30-minute protection) and FD60 (60-minute protection).
• Threshold: The bottom part of your doorframe, especially important for external doors.
• Weatherstripping: Sealing material that keeps drafts and rain at bay in external doors.

Understanding these terms helps you communicate exactly what you need when ordering your new door.

Get the Perfect Fit: Next Steps with Online Door Store

Now that you have all your measurements carefully recorded, it’s time to find your perfect door with Online Door Store. Our extensive range includes internal, external, and fire-rated doors in both standard and custom sizes.

Not sure about any of your measurements? Our experienced team is here to help. We can guide you through any tricky measuring situations or advise you on the best door type for your specific requirements.

For custom sizes or period properties, our made-to-measure service ensures you’ll get exactly what you need. We understand that every property is unique, particularly when it comes to older buildings or non-standard openings.

Ordering your door is simple. Input your measurements on our website, choose your preferred style and finish, and we’ll handle the rest. We offer fast, reliable delivery across the UK.

FAQs

How much smaller should a door be than the opening?

For internal doors, allow approximately 2mm clearance on each side and 6mm at the top. For external doors, you’ll need slightly more space to accommodate weatherstripping – typically 3mm on each side.

How much gap do you leave for a door?

Standard gap allowances are 2mm on each side, 6mm at the top, and 10mm at the bottom. However, if you’re fitting over the carpet, you might need to increase the bottom gap to 15mm.

How much clearance does a door need to open?

The door will need a clearance arc matching its width, plus a little extra for handles and fingers. For standard doors, we recommend allowing at least 1 meter of clear space for comfortable operation. For wider doors, the clearance arc should account for door width plus handle space.

Do door measurements have to be exact?

Your measurements should be as precise as possible, ideally to the nearest millimetre. Even small discrepancies can affect how well your door functions. Remember, it’s always better to measure twice and order once.