What's the difference between nominal, standard, full and actual?

Fence post cap sizes can be confusing. So far this year approximately half of our customers have called asking "what's the difference between a nominal size and an actual or full size?"

In USA, a nominal size, such as a Nominal 4x4 is just a name. You may be surprised to learn that it is not actually a 4 inch square cap nor your fence post a full 4 inches square.  Many lumber yards cut the posts to be a little under 4 inches, sometimes as small as 3.5 inches although we have found much variance across the country.

Example
Nominal 4x4  -  Actual Size 3.5 inches
Full 4x4  - Actual Size 4 inches
Nominal 6x6 - Actual size 5.5 inches
Nominal 4x6 - Actual size 3.5 x 5.5

Why the difference?

Years ago, a 4x4 did indeed measure a full 4 inches. Over time, builders & engineers realized that they could get just as much strength from a slightly smaller piece of wood.

Untreated cedar posts may still run at a full 4 inches square, but treated posts can vary from 3 3/8 to 3 3/4 inches depending on the lumbar yard. This is variable all over the country.

How to avoid buying the wrong size fence post cap

I recommend measuring your fence posts before you buy your caps. Take a random sample of your posts and meausure with a ruler or tape that shows 1/8 inch.  If your post measures 3.5 inches, you want a nominal 4x4 cap.

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