Pergola Roof Size vs. Usable Space
A pergola's stated size is its outer roof, not the clear floor space between its own posts - neither of Wisteria Lane's two pergolas publishes that interior distance, and a house wall or fence still needs its own clearance on top of it.
The number on the box isn't the number you stand inside
10' x 12' and 12' x 16' are both roof measurements - confirmed against Creators API itemDimensions, which match the 12' x 16' pergola's stated size exactly (192 x 144 in). The roof is supported by 4 posts set in from its own edge, so the clear space between those posts is smaller than the roof above it. Neither pergola in this range publishes that interior, post-to-post distance - only the outer roof size.
What that means for a "does it fit" check
The sizing page runs a fit check against the outer roof footprint only, because that's the one figure Wisteria Lane actually states. That check tells you whether the roof itself would clear an available space; it does not tell you how much floor stays usable underneath once the posts are standing in it, and it doesn't account for the gap most installations need from a house wall or fence line on top of that.
A worked example
Against a 14' x 14' clear space, the 10' x 12' pergola fits with room to spare (rotated to run its 12' side into the 14' depth); the 12' x 16' pergola does not, in either orientation, since its 16' side exceeds 14' either way it's turned. That's a roof-footprint comparison, not a promise about the floor space between the posts - see the sizing page for the full worked table.
What this guide deliberately doesn't do
It doesn't estimate the post-to-post distance from the roof size and a typical post thickness. Post placement varies by design, and a made-up number would read as a fact this site doesn't have. Measure the specific installation location, and check the manufacturer's own assembly diagram (in the box, or on the listing's product documents) for post placement before ordering.
Questions
Is a pergola's stated size the roof or the floor space?
The roof - both Wisteria Lane pergolas in this range state an outer roof footprint (10' x 12' or 12' x 16'), not the clear space between the support posts.
Does either pergola publish the distance between its posts?
No - neither the 10' x 12' nor the 12' x 16' pergola states that figure. Only the outer roof size is published.
Does the sizing page's fit check account for the posts?
No - it checks the outer roof footprint against an available space only. A “fits” result means the roof clears the space, not that the full roof area is usable floor once the posts and any house or fence clearance are accounted for.