Every cap I build is made to your exact dimensions — which means getting the measurements right is the most important step. Don't worry if you've never done this before. It takes about 10 minutes and a tape measure. If you're ever unsure, text me a photo and I'll walk you through it.
Download Your Free Measuring Worksheet
I put together printable PDF worksheets for each chimney type — with diagrams, dimensions, and everything you need to get it right the first time. Print it out, take it up to the roof, and fill it in on the spot.
→ Single Flue Chimney Chase Cover Measuring Worksheet (PDF)
→ Multi-Flue Chimney Cap Measuring Worksheet (PDF)
Have your measurements ready? Browse my custom chimney caps → — custom fabricated to cover your entire chimney top. Ships anywhere in the USA.
What You'll Need
- A tape measure
- A pencil and paper (or download the free worksheet for your chimney type above)
- Your phone to take a photo of the chimney top
Step 1: Measure the Chimney Crown
The crown is the flat masonry surface at the very top of your chimney — the surface the cap will sit on. This is your most important measurement.
- Length: Measure the full outside length of the crown
- Width: Measure the full outside width of the crown
Measure to the nearest 1/8 inch. If your measurement falls between marks, always round up — it's easier to adjust a slightly loose fit than to force a cap that's too small.
Top Mount Caps — Measuring Note
If you're ordering a top-mount cap, measure the area where you want the screen to sit on the chimney top — not the outside of the crown. Add 6" to both the length and width. The cap extends 3" beyond the screen opening on all four sides.
Not sure whether you need a top mount or side mount? Read the guide →
Step 2: Measure the Flue
The flue is the clay pipe(s) or metal pipe(s) that stick up from the crown or chase cover. Measure the outside dimensions of each flue tile or pipe, and if applicable, the termination cap on metal flue pipes.
- Length and/or width of each flue protruding above the crown
- Height: how far the flue(s) stick up above the crown surface
If you have multiple flues, measure each one and note their positions.
Step 3: Check for Obstructions
Before ordering, look for anything that could affect the fit:
- Multiple flues — are they close together or spread apart?
- Uneven or sloped crown surface
- Nearby roof lines, vents, or antennas
- Existing hardware or mortar buildup on the crown
Pro Tips
- Measure twice. Seriously. A second pass takes 60 seconds and prevents expensive mistakes.
- Always round up. When in doubt on a measurement, go to the next 1/8 inch up.
- Send me a photo. Text a clear photo of your chimney top to (609) 352-9840. I can often spot potential fit issues before I cut a single piece of metal — this is free and takes about 5 minutes.
Still Not Sure? I'll Help.
I've helped homeowners and contractors measure chimneys for 32 years. If something doesn't look right or your chimney has an unusual configuration, reach out before you order. I'd rather spend 10 minutes on the phone getting it right than have you deal with a return.
Call or text me at (609) 352-9840 or use the contact form. I ship custom caps anywhere in the USA.
Browse my custom chimney caps → — custom fabricated to cover your entire chimney top. Ships anywhere in the USA.
Sean has 32 years of experience fabricating and installing sheet metal components, copper roofing, and custom architectural metalwork — including historic preservation projects on schools, churches, and government buildings. Every cap that ships from Archaic Metal is built by hand in New Jersey.