I read that I measure the quench by adding the compressed thickness of my gasket to the deck height. How is this right? That would mean that if I had a deck height of .025 then I would have to install a .015 gasket to get the recommended .040. The .015 gasket would give me 11:1CR.

Something ain't right

 

You need to know the rest of the engines specs to determine the compression ratio. But yes a .025 piston to deck clearance @tdc combined with a .015" head gasket will give you optimin quench clearance (.040").

What are the rest of the required specs?

piston volume (valve relief or dome volume)
bore size, stroke, head gasket bore diameter, cylinder head chamber volume)

What grade of fuel (octane) are you planning on using?
There are many ways to tweek the final cr to get what you want. May have to change pistons, machine piston top,
(create a dish or remove some piston dome height)
relieve combustion chambers to add volume, swap head gaskets.
Have you actually measured the piston deck clearance on your motor?

 

No that's right, that's what makes it a PITA. You use bigger cc heads to bring your cr back down, or reverse dome pistons.

Usually you zero deck the block, and use a .041" gasket, if you were shooting for perfect quench.
I'm using pistons that are an extra .020" in the hole, and had the block decked .010" to clean it up, so i'm at .035" in the hole or so (have yet to check), and a .040 or so gasket. Not ideal with my heads, but we'll see.