An experienced carpenter, framer or builder can usually use a rough "rule of thumb" to estimate how much wood will be needed when building a wall. However, for the novice do-it-yourselfer or lightly experienced craftsman, it is often helpful to actually sketch out the project to more accurately gauge the amount of materials your project will require. By planning what you will build, and how you will build it, you will be able to avoid the pitfalls of underestimating your project.
Draw the wall out on a piece of paper. Include the framing that will be needed around any windows and doors. Use a ruler or "architect's scale" to create straight lines and be more accurate. Use a pencil so you will be able to erase incorrect lines.
Estimate the "top plate." This is the wood that runs across the top of the wall. Determine whether to have one or two "top plates." Load-bearing and exterior walls will usually require two. Use a whole piece of wood for a top plate to cover the entire length when possible. If the wall is longer than one piece of wood, use a dual top plate and stagger the joint.
Estimate the amount of wood you will need for your bottom or "sole" plate. This is the wood that runs horizontally on the bottom of the wall. Use one whole piece of wood whenever possible. There is usually only one sole plate, but it can be doubled when desired or required by code.
Estimate how many "wall studs," or vertical wood members, you will need. Determine whether these will be pre-made studs or studs cut to length on-site (this will depend on wall height). Wall studs are usually placed 16 inches on centre, but can be placed further apart in non-load bearing walls. Plan to double studs on each side of doors and windows. Use three studs at corners.
Calculate the wood needed for headers and sills (above and below windows, doors). Actual header size will vary depending on location, bearing capacity and the width of the door or window. Code books can help when determining header size.
Refer to your completed drawing. Count how many pieces of wood you will need for each part of the wall (plates, studs, headers). Total all of the amounts. Use a calculator if necessary. Add a 20 per cent overage to allow for waste and mistakes.
Basic wall framing diagrams can be useful for reference. Local code enforcement offices can sometimes help in design. Use scrap pieces for blocking and fill where necessary.
Locate hidden utilities before construction. Always refer to local code for restrictions and requirements. Unpermitted work may invalidate your homeowner's insurance policy.