Examine your pyramid. If all the sides are irregular, you can use given dimensions to figure out the surface area of each side individually and then add up these calculations.
Find the perimeter of the base if you have a regular square pyramid. For example, if you have a pyramid with base sides measuring 10 inches, you would multiply 10 by 4 to get 40 square inches.
Find the slant length of the square pyramid. This is the distance from the top of the pyramid to the median of the side of the base. Write this down. For example, suppose the slant length is also 10 inches.
Calculate the slant length if you are not given that information directly. Make a triangle using the slant length and the pyramid height. The third side should be half of a side in the base. If you know the pyramid height, you can use the Pythagorean theorem to find the slant length. Take the height and the side that is half the base side and square them both, then add them together. The square root of that is the slant length. For example, suppose the pyramid height is 5√3. The Pythagorean theorem says the slant length will equal the square root of (5√3)^2 + 5^2, or 75 + 25 = 100. The square root of 100 is 10.
Find the area of the pyramid base. In the example, the 10- by 10-inch square base would contain 100 square inches.
Multiply the perimeter of the base and the slant length, and divide this by 2. In the example, you would calculate 40 x 10/2, or 200 square inches.
Add the area of the base to your answer in Step 6. Concluding the example, you would add 200 and 100 to get 300 square inches.