Construction Reference Tables
The numbers you look up over and over: standard sizes, actual dimensions, coverage rates and code minimums.
- Standard Door Sizes and Rough Openings Interior and exterior door sizes with rough openings and real clear widths, in inches.
- Window Sizes, Rough Openings and Egress Standard sizes, rough openings, and the egress numbers worked out properly.
- Lumber Sizes: Nominal vs Actual Real dressed sizes for every nominal, dry and green, from the PS 20 standard.
- Plywood and OSB Thickness Real thickness ranges from the PS 1 and PS 2 standards, plus the span rating that decides what your framing needs.
- Nail and Screw Sizes Penny sizes, screw gauges and pilot holes, with the diameters the IRC actually specifies.
- Stair Rise and Run: Code Limits and the Layout Table IRC riser and tread limits, plus total rise converted into riser count and stair length.
- Rebar Sizes and Markings ASTM A615 diameters, areas and weights, the reason the odd sizes are odd, and how to identify a bar you did not buy.
- PVC and Copper Pipe Sizes Outside diameters and walls for PVC schedule 40 and 80 and copper K, L and M, and how to identify a pipe by measuring it.
- Ceiling Tile Sizes and Grid Layout Real panel dimensions, how much flange they land on in each grid, and the border-cut arithmetic for the layout.
What these tables have in common
Every page in this section started from the same kind of problem: a number that gets repeated everywhere, and a published standard that turns out to say something more complicated than the repetition does. The tables are here so you can look the number up. The writing under each one is there because the number on its own is usually not enough to act on.
What the material actually measures
Almost nothing in American construction measures what it is called, and each material lies in its own particular way.
A 2x4 is 1-1/2 by 3-1/2 inches dry — but a green one is 1-9/16 by 3-9/16, and the amount planed off is not a constant either: 1/2 inch off the width up to 7 inches nominal and 3/4 from 8 inches up. That is why nominal and actual lumber sizes need a table rather than a rule of thumb.
Sheet goods are stranger still. The fraction stamped on a sheet of plywood is not a thickness: the standard defines it as the name of a range, and wherever two categories sit a 32nd of an inch apart their ranges overlap, so a sheet marked 15/32 can legitimately measure more than one marked 1/2. What you actually want off that stamp is the span rating, which is the number that decides whether the sheet suits your framing spacing. Both are in plywood and OSB thickness.
Pipe is the worst of the three, because there are two naming systems in the same house and they were never meant to meet. A 1/2 inch copper tube is 0.625 inches across and a 1/2 inch PVC pipe is 0.840. Copper follows a rule you can do in your head; PVC does not follow one at all, and five pairs of pipe sit closer together than a single mark on a tape measure. PVC and copper pipe sizes is built around identifying the piece you are holding rather than around specifying a new one.
Reinforcing steel is the one case where the shorthand is almost true. The bar number is the diameter in eighths of an inch — exactly, for #3 through #8, then only loosely, and for the #14 not at all. Every chart prints the rule and the exceptions side by side without connecting them; rebar sizes and markings explains the connection, which turns out to be about square bars, and gives you the way to identify a bar you did not buy.
What the code will let you build
Three of these tables exist because a code minimum is written about something other than the thing you buy.
You buy a door slab, you frame a rough opening, and the code measures the clear width you can walk through, which is roughly two inches smaller than the number printed on the door: standard door sizes and rough openings. An escape window has three published minimums — 5.7 square feet, 24 inches high, 20 inches wide — and they are not a checklist, because meeting two of them at the limit puts the third out of reach: window sizes, rough openings and egress. And a stair riser is not a height you choose but the result of a division you are stuck with: stair rise and run.
What the part is really sized to
Two tables cover the things you order by a name that is not a measurement. A 16d common nail and a 16d box nail are the same length and 44 percent apart in steel, and the code cares about the second number, not the first: nail and screw sizes. And a 2 by 4 lay-in ceiling panel measures 47.719 by 23.719 inches, because the missing quarter inch is what lets it pass through the grid at all: ceiling tile sizes and grid layout.