Use the diagram on the right to correctly enter your roof dimensions  this will help you calculate board length more accurately.
The estimates are based on your house foot print (length and width) and roof slope. Prices are based on quotes from multiple lumber yards and building material suppliers.
Gable width (Span):  ft.  in.  
Roof Length:  ft.  in.  
Roof Overhangs:  ft.  in.  
Roof Pitch  / 12" slope.  
Rafter Spacing  
Board Size (nominal)  

x
Low End
Mid Range
High End
Materials
$1854
$2015
$2559
Labor
$2684
$2917
$3705
Cost / S.F.
$3.05
$3.31
$4.2
Total Cost
$4537
$4932
$6264
See Costs in Your Area!
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How To Use Rafter Calculator
This tool will give you total number of rafters needed for the job (including ridge boards), length of each rafter, length of lumber (boards) for each rafter, as well as total cost for all materials, presented in easy to understand form.
It is excellent for framers, builder, contractors, GC's and architects and will be helpful in planning new construction projects.
1) Enter house footprint: Length is the roof eave (gutter) side. Width or Span is the gable side of the roof, which is used in calculating rafter length and cost.
2) Enter overhang length: Most houses have overhangs (soffits) which are needed to protect the house exterior walls and foundation from water runoff from the roof. Enter desired overhang length  this will affect your rafter length and lumber needed for the job.
3) Enter roof pitch / slope: Roof pitch is the value of roof rise over roof run, using 12 as the base for roof run. Example: If your roof rises 5" for every 12" of run, enter 5 as roof pitch. If your roof pitch is in degrees, use our roof pitch calc to convert degrees to "pitch" value.
4) Select rafter spacing and width:
Rafter spacing (and roof length) will be used to determine quantity of rafters needed for your project.
Lumber size/ width (2x8", 2x10" or 2x12" boards) will be used to estimate cost of each rafter, as well as total cost (excluding local sales tax).
Rafters LONGER than 20 feet: Home improvement stores DO NOT sell pine boards longer than 20 feet. If you need rafters that are 20' 1" or longer, you will need an LVL (Laminated Veneer Lumber) engineered rafter board, which is this yellow color plywoodlike board made for structural purposes.
LVL is VERY expensive, but solves the limitation of 20 feet, in a common pine board. LVLs come in 24', 28', 30' and 32' standard lengths. If you need longer LVL, they can be custom ordered.
The calculator will automatically switch your board from PINE to LVL when you exceed 20 feet long threshold on rafter length.
LVL prices are calculated PER foot PER size. There is no "board price", meaning that a 24' 2x10" board will cost the same per foot as 32' 2x10" board. The only difference is length.
LVL Rafter prices (per linear foot):
Prices below were sourced from National Lumber in Newton, MA. These are "retail" prices and if you have an account and are working with an outside sales person, you can typically get 37% discount. Sizes are NOMINAL, which means that a 2x8 is actually 1.75" x 7.25" board.
2x8  $4.37 / ln. ft.
2x10  $5.23 / ln. ft.
2x12  $6.48 / ln. ft.
2x14  $8.35 / ln. ft.
2x16  $9.24 / ln. ft.
Limitations of the calculator
This tool is designed for lumber length of upto 20 feet, which can be commonly purchases at local home improvement stores and lumber yards. If your rafter length is calculated to be longer than 20 feet, then there are two options for you:1) Most lumber yards and building materials suppliers sell an actual 2" x 12" by 24 feet boards for $4555 each. Longer size boards are NOT available.
2) If you need a rafter longer than 24 feet, you will have to use engineered wood rafters.
For pricing we used Home Depot online prices, which are comparable to Lowe's prices for the same size boards. Lumber yard prices would be slightly higher, but supposedly be better quality wood.
For special order pricing (24' boards or engineered wood rafters) contact local building material suppliers or lumber yards.
Additional Resources
If you are in planning stages of building your house, and need to figure out how much roof shingles cost, use this tool to get an accurate estimate for 3tab and architectural shingles.If you need to estimate roof replacement cost, use our price estimator. It will give you low  end, mid  range and high  end costs for top materials, including: shingles, slate, clay tile, wood, and metal roof.
Your Estimated Roofing Cost
Roof Price:
Cost per sq. ft.
Roof Size:
Roofing Material:
Cost per sq. ft.
Roof Size:
Roofing Material:
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This roofing guide is presented by Leo B.
I've been a roofer for 13 years, and specialize in Metal Roofing and Flat Roofing.
Have a roofing question or issue? Ask me any roofing question!
Roofing Contractors  join our free Local Roofers directory to get more customers!
I've been a roofer for 13 years, and specialize in Metal Roofing and Flat Roofing.
Have a roofing question or issue? Ask me any roofing question!
Roofing Contractors  join our free Local Roofers directory to get more customers!
There are: 8 Comments
Is this calculator only factoring rough material cost? Does it calculate rough labor cost? .
Melissa,
This calculator only estimates cost of materials. Labor costs are nearly impossible to estimate for roof rafters, because most such jobs are done during HOME BUILDING stage, and are part of overall framing cost. Framers do not breakdown cost of walls / cost of rafters, etc. They price work by the job or square foot, depending on house layout.
In retrofit applications, there are 100s of external factors that affect labor cost.
Hence, we did not even fathom to include cost of installation / demolition work – it is completely outside the scope of this tool.
Leo
Does your roof calculator adjust for snow load
How can I purchase the roof calculator?
Tommy,
What exactly are looking to purchase? Are you a contractor, and want calculator for your site? If so, we are finishing a product that you will be able to put on your website, with your own prices in it.
I will be making announcement on this blog, but you can contact me via email for more info – info @ roofcalc.org
Cheers, Leo
84 lumber have 2×10 and 2×12”s well over 20 feet.
Greg,
I’m not sure what your question is.
I would like to get your roof calculator