board ends

Common Options

All your careful measuring will be wasted if you start with a piece of lumber that is not square -- one edge will be longer than the other. Check the board end by holding a combination square with the body or handle firmly against a factory edge. If the end isn't square, mark a square line and trim the board.

combination square

With this tool you can easily check for either 45- or 90-degree angles. Also, by sliding the blade, you can check depths. This tool can go out of square if it is dropped, so check it once in a while against a square factory edge (such as the corner of a sheet of plywood).

framing square

For larger jobs, use a framing square. Lay the square up against two members where they meet. If the tongue and the blade of the square rest neatly against the members, the sides are perpendicular. Or, place the square on the outside. Again, if the square touches the members at all points, the unit is square. When using a framing square for measuring, be sure to read the correct scale--inside or outside.

3-4-5 method

For large projects, test if a corner is square by using geometry. You don't need to remember the Pythagorean theorem. Just remember "3-4-5." On one side, mark a point 3 feet from the corner. On the other side, mark a point 4 feet from the corner. If the distance between the two marks is exactly 5 feet, it is square. For extra large projects, use multiples such as 6-8-10 or 9-12-15.

As a double check, measure the length of the diagonals. If the project is square, the distance between two opposite corners (marked A in the drawing above) will equal the distance between the other two corners (B).

plumb

To see if a piece is perfectly vertical--plumb--hold a level against one face of the vertical surface and look at the air bubble in the level's lower glass vial. If it rests between the two guide marks, the piece is plumb.

level

In most cases, you can simply set your carpenter's level atop the piece to see if it's level. Raise or lower the piece until the bubble rests between the marks. Mark the position of the piece and remove the level (you don't want to risk knocking it to the floor). Add a fastener to the cleat near the level mark, level the cleat, and finish fastening.

long distances

If you need to see if an entire floor is level, select a long, straight board. (Sight down its length to see that it's not bowed.) Place a carpenter's level in the center of the board and raise one end or the other until the bubble is centered between the two lines. Slide the board around until you are sure you have found the high point of the floor. Level the board from this high point and measure the distance from the floor to the bottom of the raised end of the board to see how far out of level the floor is.

water level

This tool enables you to quickly check for level in awkward situations or over long distances. Basically a long hose and two transparent tubes filled with water, this tool works on the principle that water seeks its own level. Mark at water level.

tight spot

In places where you can't fit in a carpenter's level, use the level that comes on some combination squares or a torpedo level (a short version of a carpenter's level). Or, if you know that an adjoining member or wall is plumb, measure to see that the piece is square to it.

cabinet

When installing cabinets, make sure they are plumb in both directions or the doors will shut or open by themselves. With the cabinet fastened to the wall loosely, hold a level against a vertical framing piece. Tap in shims until the bubble indicates that the cabinet is plumb.