Carpentry Math

The carpentry math and formulas commonly used in nearly every carpentry project are listed below.

How to calculate:



Carpentry Math - Right Triangles - The Pythagorean Theorem

The Pythagorean Theorem is used extensively in carpentry and construction. Almost every carpentry project involves some combination of squares and triangles.

The squared value of the hypotenuse of a right triangle is equal to the sum of the squared values of the other two sides. Essentially, side A squared plus side B squared equals side C squared.

Pythagorean Theorem

A² + B² = C²

You can also calculate the length of an adjacent side by subtracting the hypotenuse squared minus either side squared. For example, side A squared equals side C squared minus side B squared.

A² = C² - B²

If this sounds complicated, consider the 3-4-5 rule of a right triangle. It is the best way to square two walls. Here's how it works - if one side of a right triangle is three feet and the adjacent side is four feet, the hypotenuse (or long side of the triangle) will be five feet, then angle 'A' is 90 degrees (see diagram at right). If you need to square walls in a large room, you can use proportions of this same formula, such as 6-8-10.

5² = 4² + 3² or 10² = 8² + 6²

Pythagorean Theorem



How to Calculate the Area of a Triangle

The Area of a triangle is equal to one-half the product of the Base and Height.

A = .5 x (B x H)

Area of a Triangle



How to Calculate the Area of a Rectangle

To calculate the Area of a rectangle, multiply the Length by the Width.

A = L x W

Area of a Rectangle



How to Calculate the Volume of a Cube

To calculate the Volume of a cube or box, multiply the Length times the Width times the Height.

Volume = L x W x H

Volume of a Cube or Box



How to Calculate the Area of a Trapezoid

To calculate the Area of a trapezoid, multiply its Height by one-half the sum of the parallel sides.

A = .5 x (L1 + L2) x H

Area of a trapezoid



How to Calculate the Circumference of a Circle

To calculate the Circumference of a circle, multiply the Diameter times 3.1416 (pi).

C = 3.1416 x D

Circumference of a Circle



How to Calculate the Area of a Circle

To calculate the Area of a circle, multiply the Circumference by one-half the Radius.

A = C x .5(R)

Or, multiply the radius squared by pi:

A = 3.1416 x R²

Area of a circle



How to Calculate the Volume of a Cylinder

To calculate the Volume of a cylinder, multiply the Radius squared x 3.1416 (pi) x the Height of the cylinder.

V = 3.1416 x R² x H

Volume of a Cylinder

 See Also (on mycarpentry.com)

Carpentry Calculators - Calculators used in carpentry.

Framing Carpentry - How to frame residential structures.

Span Tables - Calculate maximum rafter and joist spans.

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