Framing Calculator

What the framing calculator does

Before you buy lumber for a wall, you need to know how many studs and how many plates it takes, and counting it off a plan stud by stud is slow. This does the count. You give it the wall length, the stud spacing, and how many studs you want at each end, and it returns the number of studs along with the boards for the top and bottom plates.

It turns a wall length into a shopping list. Below is how it works out the count and what it does and does not include.

How to use it

1. Enter the wall length, with its unit.
2. Enter the stud spacing, the on-center distance between studs, usually 16 inches.
3. Choose the studs at each end, one, two, or three, for the end posts where walls meet at corners.
4. Press Calculate for the count, or Reset to clear it.

How the studs and plates are worked out

The studs come from dividing the wall length by the spacing and rounding up, which gives the studs along the run, then adding the studs you asked for at each end:

Studs = (wall length ÷ spacing, rounded up) + the end studs

The plates are the horizontal boards that cap the wall top and bottom. The calculator works out how many 8 foot boards it takes to span the wall, then counts a double layer for the top plate and a single layer for the bottom, which is the usual build for a load-bearing wall.

Stud spacing and why 16 inches

Sixteen inches on center is the standard for a reason, and it is not just habit. It is the spacing the building code sets for ordinary load-bearing walls, and it lines up neatly with sheet materials. A standard sheet of drywall or sheathing is 48 inches wide, which is exactly three 16 inch bays, so every sheet edge lands on the centre of a stud with a solid place to fasten it.

On center means measured centre to centre, not the gap between studs. Some walls, such as non-load-bearing partitions or thicker framed walls, can go to 24 inch spacing, which is why the calculator lets you set it rather than assuming. Whatever you choose, the spacing drives the whole count.

A worked example: a 20 ft wall

Say the wall is 20 feet long at 16 inch spacing, with a single stud at each end.

Twenty feet is 240 inches, divided by 16 gives 15, so there are 15 studs along the run plus the end studs, for 16 studs in all. Choosing two studs at each end for corner posts would add a couple more. For plates, it takes three 8 foot boards to span 20 feet, so that is five boards for the double top plate and three for the bottom.

So the bare wall is 16 studs and 8 plate boards, before the extras the next section covers.

What this covers and what to add

This counts a plain, solid wall, the studs and the plates. Real walls usually have a few things on top of that. Doors and windows need a header across the opening and extra studs framing each side, the king and jack studs, so add those for every opening once you know where they fall. It is also worth adding a little extra lumber overall for the odd bowed or split board you set aside.

And since this is structure, the spacing, stud size, and headers on a load-bearing wall are governed by code and by what the wall carries. The calculator is for planning the material; for a wall that holds the building up, confirm the framing against your local code or with a builder or engineer.

Questions people ask

How many studs do I need for a wall?

Divide the wall length by the spacing, round up, and add the end studs. A 20 foot wall at 16 inch spacing comes to about 16 studs before openings and corners.

What does 16 on center mean?

The centre of each stud is 16 inches from the centre of the next. It is the standard spacing for load-bearing walls and lines up with 48 inch wide sheet materials.

Do I need one top plate or two?

Load-bearing walls normally use a double top plate and a single bottom plate, which is how the calculator counts the plate boards.

Does this include doors and windows?

No. It counts a solid wall. Add a header and the extra king and jack studs for each opening once you know where they go.

References

A quick note on where these figures come from. The stud spacing, the double top plate over a single bottom plate, and the way 16 inch spacing aligns with 48 inch sheet materials all follow the wood wall framing provisions of the International Residential Code. The unit conversions follow the US National Institute of Standards and Technology guide.

1. International Code Council, International Residential Code, Section R602 (wood wall framing, stud spacing, and top plates). https://codes.iccsafe.org
2. National Institute of Standards and Technology (NIST), Special Publication 811, Guide for the Use of the International System of Units (SI). https://www.nist.gov/pml/special-publication-811