How to Estimate Stairs

Lay a long, straight board on its edge on top of the deck. The end of the board should be perpendicular to the approximate area where the stairs will touch the ground. Place a carpenter's level on top of the board and adjust the board up or down until it is at level.

Stretch a tape measure from the ground up to the bottom of the board and read the height. This is the total rise the stairs will need to cover.

Divide the rise measurement by an average rise per stair -- 7 inches. For example, if the rise measurement was 32 inches, dividing by 7 would yield a number of 4.57. In this case, since the decimal amount is greater than .5, round up. That means 5 stairs are needed to cover the span. If the decimal had been less than .5, you would round down so that 4 stairs were required.

Divide the rise measurement by the number of stairs you calculated to get the actual rise per stair. In this example, 32 inches divided by 5 stairs results in a rise of 6.4 inches per stair. Most building codes accept a rise of anywhere between 6 1/2 to 8 inches per stair, so this example would fall into the correct range.

Decide whether the calculated rise per stair is acceptable. While it may be in the range, a 6.4-inch rise per stair may seem too short for you. If it is, try calculating the rise per stair again with one fewer step. In the example, 4 steps would produce a rise of 8 inches per stair. That's still in the acceptable range and may result in a more comfortable stride when taking each step.