How to Measure for Custom Fireplace Doors Correctly

To measure for custom fireplace doors correctly, you need to measure the width, height, and depth of your fireplace opening from inside the firebox where the doors will mount.

Take measurements at three different points for width and height, then use the smallest measurements to ensure your custom fireplace doors fit properly.

Table of Contents

Why Accurate Measurements Matter for Custom Fireplace Doors

Getting your fireplace door measurements wrong can cost you hundreds of dollars and weeks of waiting. Custom doors can’t be returned like regular products.

I found that most measurement mistakes happen because people rush the process. You need to be patient and double-check everything.

Think of measuring your fireplace like tailoring a suit. One wrong number means it won’t fit right, no matter how beautiful it looks.

Essential Tools You Need Before Starting

You don’t need fancy equipment to measure for custom fireplace doors. Here’s what works best:

Metal measuring tape (at least 25 feet long)
Pencil and paper for notes
Flashlight or phone light
Small ruler for depth measurements
Someone to help hold the tape

Skip the cloth measuring tapes. They stretch and give wrong numbers. Metal tapes stay accurate even in tight spaces.

Safety Preparation

Make sure your fireplace is completely cool before measuring. Wait at least 12 hours after your last fire.

Clean out any ash or debris that might block your view. You need to see exactly where the fireplace opening starts and stops.

Step-by-Step Width Measurement Process

Width is the most important measurement for custom fireplace doors. Get this wrong, and nothing else matters.

Finding Your Measurement Points

Measure the width at three different heights inside your fireplace opening:

Bottom of the opening (just above the floor)
Middle of the opening
Top of the opening (just below the lintel)

Many fireplaces aren’t perfectly square. The opening might be wider at the top than the bottom, or vice versa.

Recording Width Measurements

Write down all three width measurements. Use the smallest one for ordering your doors.

For example, if you get 36 inches at the bottom, 36.25 inches in the middle, and 35.75 inches at the top, use 35.75 inches as your width.

This ensures your doors will fit through the tightest part of the opening.

Measuring Height the Right Way

Height measurements work the same way as width. You need three measurements to account for any irregularities.

Height Measurement Points

Measure the height at these three spots:

Left side of the opening
Center of the opening
Right side of the opening

Start each measurement from the very bottom of the fireplace floor. Go straight up to where the opening ends.

Dealing with Arched Openings

Does your fireplace have an arched top? This changes everything.

For arched fireplaces, measure to the lowest point of the arch. Your rectangular doors need to fit under that curve.

Some custom door companies can make arched doors, but they cost more and take longer to build.

Getting the Depth Measurement Right

Depth tells you how far back your fireplace doors can extend. This affects which mounting style you can use.

Front-Mounted vs. Flush-Mounted Doors

Front-mounted doors sit against the front face of your fireplace. They need less depth but stick out more.

Flush-mounted doors sit inside the opening. They look cleaner but need more depth to work properly.

How to Measure Depth

Measure from the front edge of your fireplace opening straight back to where the firebox narrows or where the damper starts.

You need at least 3 inches of depth for most flush-mounted doors. Front-mounted doors work with any depth.

Understanding Different Door Mounting Styles

Your measurements determine which mounting style works for your fireplace. Let me break down the options.

Overlap Mount Doors

These doors mount on the front face of your fireplace. They overlap the opening by about 1 inch on all sides.

For overlap mount doors, add 2 inches to both your width and height measurements. This gives you the actual door size.

Flush Mount Doors

Flush mount doors fit inside your fireplace opening. They mount to the inside walls of the firebox.

Use your exact opening measurements for flush mount doors. Don’t add anything to the numbers.

Insert Mount Doors

These work with fireplace inserts that already have their own frame. Measure the insert opening, not the original fireplace.

Common Measurement Mistakes to Avoid

I researched the most frequent errors people make when measuring for custom fireplace doors. Here are the big ones:

Measuring the Hearth Instead of the Opening

Your hearth is usually wider than your fireplace opening. Make sure you’re measuring inside the actual opening where flames come out.

Forgetting About Existing Doors or Screens

Remove any existing doors or screens before measuring. They can block your view of the true opening size.

Rounding Numbers

Don’t round your measurements to the nearest inch. Custom doors need exact numbers. Use fractions like 35.75 inches or 36.25 inches.

Measuring Only Once

Always measure twice, preferably on different days. Double-checking saves you from expensive mistakes.

Special Considerations for Older Fireplaces

Older homes often have unique challenges when measuring for custom fireplace doors.

Dealing with Uneven Openings

Houses settle over time. Your fireplace opening might not be square anymore.

Use your smallest measurements and consider having a professional check the structural soundness before ordering expensive custom doors.

Masonry vs. Prefab Fireplaces

Masonry fireplaces (built with bricks) often have irregular shapes. Prefab fireplaces (factory-made) are usually more uniform.

Masonry fireplaces need extra careful measuring because no two are exactly alike.

When to Call a Professional for Measuring

Some situations are too tricky for DIY measuring. Here’s when to get help:

Your fireplace opening is severely damaged or cracked
You’re planning major renovations
The opening is extremely unusual or custom-shaped
You’re not confident in your measurements

Many custom door companies offer measuring services. It costs extra but guarantees accuracy.

Questions to Ask Professionals

If you hire someone to measure, ask these questions:

Do they guarantee their measurements?
What happens if the doors don’t fit?
Can they recommend the best mounting style?
Do they check for any safety issues?

Double-Checking Your Work

Before you order those custom doors, verify everything one more time.

The 24-Hour Rule

Wait a day, then remeasure everything from scratch. Fresh eyes catch mistakes tired eyes miss.

Compare with Standard Sizes

Most fireplaces fall into common size ranges. If your measurements are way off from standard sizes, double-check your work.

Take Photos While Measuring

Photos help you remember exactly where you measured. They’re also useful when talking to door companies.

Working with Door Manufacturers

Good custom door companies will review your measurements before building anything.

Information to Provide

Give your door company these details:

All width measurements (with smallest clearly marked)
All height measurements (with smallest clearly marked)
Depth measurement
Photos of your fireplace
Preferred mounting style
Any unusual features or concerns

Ask About Their Process

Reputable companies will ask questions about your measurements. They want to make sure you get doors that fit.

Be suspicious if they don’t ask any follow-up questions or seem to rush the ordering process.

Measurement Type	Number of Points	Use This Number
Width	3 (top, middle, bottom)	Smallest measurement
Height	3 (left, center, right)	Smallest measurement
Depth	1 (front to back)	Actual measurement

Conclusion

Measuring for custom fireplace doors takes patience, but it’s not complicated. Remember to measure width and height at three different points, use the smallest numbers, and always double-check your work.

Take your time with this process. Rushing leads to expensive mistakes that can’t be easily fixed. When in doubt, measure again or ask a professional for help.

Your custom fireplace doors should last for decades when they fit properly. Getting accurate measurements is the foundation of that long-term success.

What if my fireplace opening is not perfectly rectangular?

Use the smallest width and height measurements to ensure the doors fit through the tightest spots. Custom door companies can often accommodate slightly irregular openings with adjustable frames or trim pieces.

How much clearance should I leave around the doors?

For flush-mount doors, leave about 1/8 to 1/4 inch clearance on all sides. Overlap doors don’t need clearance since they mount on the fireplace face. Your door manufacturer will account for proper clearances in their design.

Can I measure around existing glass doors that are stuck?

It’s better to remove stuck doors first, even if you need professional help. Measuring around existing doors often gives inaccurate numbers. Most old doors can be removed with basic tools and patience.

Do I need different measurements for gas vs wood fireplaces?

The measuring process is the same for both gas and wood fireplaces. The difference comes in door design and ventilation requirements, which your manufacturer will handle based on your fireplace type.

What should I do if my three width measurements vary by more than half an inch?

Large variations suggest your fireplace opening is significantly out of square. Consider having a mason or fireplace professional assess the opening before ordering custom doors. You might need structural adjustments first.