How do I figure out stair treads and risers?

September 27, 2005 (11:59 pm EST)
Filed under: Ask a Contractor by News Staff

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
1.0	1

Tags: build stairs, building codes, calculate stairs, convert to decimal, convert to inches, fraction to decimal, stair risers, stair treads, tread size

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How do I figure out stair treads and risers?

Can I measure in inches and use a Calculator?

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.

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