How to Measure Your Fireplace for an Oak Beam - The Complete Guide
If you've ever stared at your fireplace opening with a tape measure and thought "where do I even start" — this guide is for you.
Getting the measurement wrong is the most common reason people end up with a beam that looks off, sits too proud of the wall, or worse, doesn't fit at all. We've spoken to hundreds of customers who nearly ordered the wrong size.
This guide fixes that. Five minutes of reading will save you an expensive mistake.
Why Getting This Right Matters
An oak fireplace beam isn't a small purchase. You're putting it in the most prominent spot in your living room — the focal point of the entire space. A beam that's even 10cm too short looks like an afterthought. One that's too deep sticks out awkwardly from the chimney breast.
The good news is measuring your fireplace correctly is straightforward once you know what you're actually measuring. Most people measure the wrong things.
Here's what to measure and exactly how to do it.
What You'll Need
Just two things:
A tape measure — ideally a metal one, not a fabric one. Metal gives you a straight line across an opening without sagging.
A notepad or your phone to record the measurements. You'll need three numbers.
The Three Measurements You Need
1. The Width of Your Fireplace Opening
This is the most important measurement and the one most people get wrong.
Measure the width of the actual opening — not the chimney breast, not the surround, not the wall. The opening itself, from inner edge to inner edge at the widest point.
Write this number down. This is your minimum beam length. Your beam needs to be wider than this number or it won't span the opening properly.
Rule of thumb: Add at least 15cm to each side of the opening. So if your opening is 80cm wide, you want a beam that's at least 110cm long. This gives the beam proper visual weight and enough surface area to sit flush against the chimney breast on both sides.
Most of our customers end up with beams between 120cm and 150cm for standard UK fireplaces.
2. The Height of Your Fireplace Opening
Measure from the floor of the fireplace opening to the top of the opening — the lintel or the arch at the highest point.
This tells you how high up the beam will sit on the wall. Most customers want the beam sitting 5-10cm above the top of the opening. Any closer and it can look cramped. Any higher and it starts to look disconnected from the fireplace.
Write this number down. You'll use it when positioning the beam on the wall during installation.
3. The Depth of Your Chimney Breast
This is the measurement people forget — and it's the one that causes the most problems.
Measure how far your chimney breast protrudes from the main wall. This tells you which beam profile will work for your space.
If your chimney breast is shallow — 10cm or less — you want a slimmer beam profile like our 7.5x10cm or 10x10cm range. These sit neatly without overwhelming a shallow breast.
If your chimney breast is deeper — 15cm or more — you can go bolder. Our 15x15cm and 20x10cm profiles look stunning on a deep breast, especially in an inglenook or a larger room.
Choosing the Right Profile
Once you have your three measurements, choosing the right profile becomes straightforward.
| Profile | Best for | Starting price |
|---|---|---|
| 7.5 x 10cm | Slim and subtle. Modern fireplaces, shallow chimney breasts, smaller rooms | From £75 |
| 10 x 10cm | The most versatile profile. Works on almost every fireplace type | From £99 |
| 12.5 x 10cm | Our most popular size. Real visual weight without being overwhelming | From £99 |
| 12.5 x 12.5cm | Chunky and bold. Period properties, large inglenooks, statement rooms | From £105 |
| 20 x 10cm | Wide and flat. Media walls and large modern fireplaces | From £110 |
| 15 x 15cm | The grand statement. Large rooms, high ceilings, centrepiece beams | From £125 |
Choosing the Right Finish
Once you have your profile sorted, the finish is the fun part.
Clear oak — Natural, light, and modern. Shows off the grain beautifully. Works best in contemporary homes and lighter colour schemes.
Medium oak — Warm and versatile. The most popular finish. Works in almost every home and complements both modern and traditional interiors.
Rustic oak — Heavily worked with a rougher texture and more character. Perfect for country homes, stone fireplaces, and anyone who wants that authentic reclaimed look.
Dark oak — Rich and dramatic. Works beautifully in darker rooms and with dark grey or charcoal walls. Makes a real statement.
Black oak — Bold and contemporary. Increasingly popular in modern homes with black steel fireplaces and minimalist interiors.
Not sure which finish suits your home? Send us a photo of your fireplace and we'll tell you exactly which finish we'd recommend. It's free and takes us two minutes.
A Note on Wall Type
Brick or stone — You'll need masonry fixings and a hammer drill. Our beams come with keyhole hangers which make installation straightforward on brick.
Plasterboard — You'll need to locate the studs behind the plasterboard and fix into those, or use cavity wall anchors rated for the weight of the beam. Our beams typically weigh 4-8kg depending on size.
Solid plaster over brick — Same as brick. Drill through the plaster into the brick beneath and use masonry fixings.
If you're unsure, send us a photo and we'll advise.
The Measurement Checklist
Before you order, confirm you have these three numbers:
- Opening width — add at least 15cm each side for your beam length
- Opening height — so you know where the beam sits on the wall
- Chimney breast depth — so you choose the right profile
If all three are confirmed, you're ready to order with confidence.
Still Not Sure?
Send us a photo of your fireplace and we'll tell you exactly what to order. We'd rather spend two minutes helping you get it right than have you receive a beam that isn't quite perfect.
Every beam is handcrafted in Wales and made to last a lifetime. Getting the size right means you'll never need to think about it again.
