Ready to order once you have your measurements? Browse our custom chimney caps → — custom fabricated to cover your entire chimney top. Ships anywhere in the USA.
It's the first question almost every customer asks, and it's the right one to start with. Order a cap that's too small and it won't fit. Too large and it looks wrong and may not seal properly. Get it right and you'll have a cap — whether you call it a chimney cap, chimney topper, chimney rain cap, or chimney cover — that looks like it was always meant to be there, because it was built specifically for your chimney.
Here's how to figure out exactly what size you need.
There Are Two Measurements That Matter
Most people think chimney cap sizing is just one number. It's actually two, and they serve different purposes:
- Crown dimensions — the outside length and width of the flat masonry surface at the top of your chimney. This determines the size of the cap's base.
- Flue dimensions — the outside length and width of the clay flue tile(s) that stick up from the crown. This determines how much clearance the cap needs to allow proper airflow.
The crown measurement is the one that drives the cap size. The flue measurement confirms the cap will clear the tile and allow your chimney to draft properly.
How to Measure Your Chimney Crown
Get a tape measure and go to the top of the chimney. Measure the full outside length and width of the masonry surface — the flat area the cap will sit on.
- Measure the full length from outside edge to outside edge
- Measure the full width from outside edge to outside edge
- If your crown is not perfectly square or rectangular, note the longest dimensions
- Round up to the nearest 1/8 inch — never round down
That's your base size. A 24" x 36" crown gets a 24 x 36 cap base.
Single Flue vs. Multiple Flues
If you have one flue tile sticking up from the crown, sizing is straightforward — your cap just needs to be large enough to cover the crown with a small overhang on each side to shed water.
If you have multiple flue tiles, you have two options: one large cap that covers all flues at once, or individual flue caps for each tile. Most homeowners prefer a single cap for a cleaner look. We build both — just let us know your configuration when you order.
What About the Height?
Cap height is driven by two things: how tall your flue tile is above the crown, and your personal preference for proportion. As a general rule, the cap should be tall enough that the spark screen clears the top of the flue tile by at least 2 inches on all sides. This ensures proper airflow and prevents the cap from restricting your chimney's draft.
If you have a specific height preference or need to match an existing architectural detail, just tell us when you order. Height is fully customizable.
The Most Common Sizing Mistakes
- Measuring the flue tile instead of the crown — these are different dimensions and will result in a cap that's too small
- Rounding down — always go up to the nearest 1/8 inch
- Forgetting to account for multiple flues — a cap sized for one flue won't cover two
- Not checking for obstructions — uneven crowns, sloped surfaces, or nearby vents can affect fit
Not Sure? Send Us a Photo.
This is the easiest option for most people. Text a clear photo of the top of your chimney to (609)352-9840 and we'll tell you exactly what size you need before you order anything. We've been doing this for 32 years — we can spot a sizing issue from a photo in about 30 seconds.
You can also download our free PDF measuring worksheet which walks you through every measurement step by step.
Ready to Order?
Once you have your dimensions, head to our catalog to choose your style and material. Every cap is made to your exact measurements and ships anywhere in the USA in a custom wooden crate via insured LTL freight.
"Sean was great to work with and very accommodating. My new chimney cap was exactly as described and of excellent quality." — Sheri
Browse our 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.