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How do I figure out stair treads and risers?

Filed under: Ask a Contractor by News Staff at 11:59 pm on September 27, 2005

Can I measure in inches and use a Calculator?

Q: I am building a wooden deck and have a general idea about how to build stairs. I want to get each step and riser to be exactly the same, but my calculator does not convert decimal numbers to fractions. I want to experiment with different sizes, please help.

A: If your calculator does not convert to inches, or fractions of inches, use the chart below, and follow these easy steps.

  • Measure total rise from ground to top of landing.In this example we will use 3'6" rise.

    Check local building codes for maximum heights, minimum requires specifications, etc.

  • Measure from edge of landing out total distance where you would like bottom landing to be.For this example we will use a 5'6" total distance from landing to landing.

    Top landing may be the edge of a deck, a doorway, or an actual landing step. Bottom landing may be the edge of a walkway or any point away from structure where bottom of stairway will end.

    Check local building codes to see if landing area specifications exist -- some stairways must end or begin within set distances from other structures, entrances, etc.

  • Determine the size of the treads you'd like to have.Typical residential exterior steps use 11" treads and 7" rises. So lets start experimenting just using the 11" tread and see how the math works.

    Most building codes require minimum and maximum tread widths and will provide formulas for proper ratios of tread to rise.

  • Divide the total distance by the tread size.5'5" = 66"

    66" / 11" = 6 (treads)

    If total distance out from top edge of landing is 66" and you want 11" treads, this would result in 6 steps of 7" rise, which would fit exactly in a 42" high total rise.

    3'5" = 42"

    42" / 7" = 6 (risers)

To experiment with different size treads and rises, use a calculator and the chart below for common 1/4", 1/8", 1/16" or even 1/32", and 1/64" sizes depending on the materials you are working with and the degree of accuracy you require when cutting materials.

Take this example for instance:

Total Rise: 49 7/8"

Total Distance: 71 3/4"

71.75 / 11" = 7 (treads)

49.875 / 7 = 7.125" (or 7 1/8") rises.

Experiment with various sizes until measurment falls within desired range of accuracy.

DECIMAL S.A.E.
0.015625 1/64
0.03125 1/32
0.046875 3/64
0.0625 1/16
0.078125 5/64
0.09375 3/32
0.109375 7/64
0.125 1/8
0.140625 9/64
0.15625 5/32
0.171875 11/64
0.1875 3/16
0.203125 13/64
0.21875 7/32
0.234375 15/64
0.25 1/4
DECIMAL S.A.E.
0.265625 17/64
0.28125 9/32
0.296875 19/64
0.3125 5/16
0.328125 21/64
0.34375 11/32
0.359375 23/64
0.375 3/8
0.390625 25/64
0.40626 13/32
0.421875 27/64
0.4375 7/16
0.453125 29/64
0.46875 15/32
0.484375 31/64
0.5 1/2
DECIMAL S.A.E.
0.515625 33/64
0.53125 17/32
0.546875 35/64
0.5625 9/16
0.578125 37/64
0.59375 19/32
0.609375 39/64
0.625 5/8
0.640625 41/64
0.65625 21/32
0.671875 43/64
0.6875 11/16
0.703125 45/64
0.71875 23/32
0.734375 47/64
0.75 3/4
DECIMAL S.A.E.
0.765625 49/64
0.78125 25/32
0.796875 51/64
0.8125 13/16
0.828125 53/64
0.84375 27/32
0.859375 55/64
0.875 7/8
0.890625 57/64
0.90625 29/32
0.921875 59/64
0.9375 15/16
0.953125 61/64
0.96875 31/32
0.984375 63/64
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