Online Roof Construction Calculators - DIY Projects & Professional Builds
Master any roofing project with RedX Apps’ comprehensive suite of Roof Construction Calculators. Ideal for both DIY enthusiasts planning their shed roofs and professionals designing complex roofing structures. Our tools offer detailed 3D modeling, automatic rafter and truss calculations, and custom blueprint generation. Access specialized calculators for Rafter, Hip, Valley, and Gambrel designs, ensuring precision and ease in every build. Now with RedX AI: describe your roof in plain language and RedX AI generates the framing design in 3D for you to refine and print.
How to Use This Tool
Pick the calculator that matches your roof
Full custom roofs go to the Roof Builder; trusses to the gable or gambrel truss builders; specialty shapes to the turret, bay, and hip tools; sheathing to the plywood angle calculator.
Enter your dimensions and pitch
Every tool starts from the same inputs - spans, runs, and a pitch in X/12 form. Or describe the roof to RedX AI in plain language and it generates the 3D framing design for you to refine.
Refine the design in 3D
Inspect each rafter or truss member in the interactive viewer, adjust pitches and overhangs, and confirm the geometry before anything gets cut.
Export blueprints and cut lists
Download dimensioned blueprints and complete cut lists as PDFs, or print them directly for the job site.
The math every roof shares
Whatever the roof shape, three relationships do almost all the work. The pitch multiplier sqrt(1 + (pitch/12)^2) converts horizontal run to sloped length - for rafters, for sheathing area, for anything measured along the roof plane. Hips and valleys travel diagonally, so they swap the 12-inch unit run for 16.97 inches and use their own multiplier. And every cut angle on the roof comes from arctan of a rise over a run - the plumb cut is arctan(pitch/12), the hip plumb cut is arctan(pitch/16.97).
Each calculator on this page applies those relationships to a specific geometry - a polygon, a bay corner, a truss profile - so you get the shape-specific answers without re-deriving the trigonometry per member.
pitch multiplier = sqrt(1 + (pitch/12)^2)
rafter length = run x sqrt(1 + (pitch/12)^2)
hip/valley length = run x sqrt(2 + (pitch/12)^2)
pitch angle in degrees = arctan(pitch / 12)
roof area = plan area x pitch multiplier
Frequently Asked Questions
Which roof calculator should I start with?
Start with the Roof Builder if you are framing a whole structure - draw the wall perimeter and it generates every rafter, hip, valley, and ridge with blueprints. Use the gable or gambrel truss builders if the roof will be built as repeated trusses on a deck. The turret, bay, and truss-hip tools handle specific shapes, and the plywood angle calculator takes over when the framing is up and you are sheathing hips and valleys.
How do I calculate rafter length by hand?
Take the run - horizontal distance from the wall plate to the ridge centerline, usually half the span - and multiply by sqrt(1 + (pitch/12)^2). A 14 ft run at 6/12 gives 14 x 1.118 = 15.65 ft, about 15 ft 7-3/4 inches of line length. Then shorten by half the ridge thickness at the top and add the tail for the overhang. Our rafter length guide walks the full layout including the birds mouth.
What roof pitch should I choose?
Most residential roofs land between 4/12 and 9/12 - shallow enough to walk and sheath safely, steep enough to shed water and take standard shingles. Below 4/12, asphalt shingles need doubled underlayment and below 2/12 they are not permitted per IRC R905.2.2; low-slope membranes take over there. Above 9/12 you gain snow shedding and attic volume at the cost of staging and material. Snow country favors 6/12 and up. Verify covering requirements locally.
Should I stick-frame my roof or use trusses?
Trusses win on speed, span, and cost for simple rectangular roofs - they arrive engineered and set in a day, clear-spanning without interior bearing walls. Stick framing wins for complex footprints with hips, valleys, and dormers, for cathedral ceilings and usable attics, and for remote sites where truss delivery is impractical. Many roofs mix both: trusses over the main body with stick-framed hip ends, which is what the truss hip rafter calculator handles.
What size rafters do I need?
Depth depends on horizontal span, spacing, lumber species and grade, and roof load. As reference points from IRC Table R802.4.1(1)-type values, a 2x6 SPF No. 2 at 16 inches on center spans roughly 9 to 13 ft and a 2x10 roughly 15 to 21 ft, varying with snow load and dead load. Get the geometry from these calculators, then size the members against our span tables and your local ground snow load - and verify with your building department.
Can RedX AI really design the roof for me?
You describe the roof in plain language - a 24 by 32 hip roof at 6/12 with 16-inch overhangs, say - and RedX AI generates the framing design in 3D: rafters, hips, valleys, and ridges placed and dimensioned. From there you refine it like any design you built manually, adjusting pitches or planes, then export the blueprints and cut lists. It is a faster starting point, not a replacement for checking the design against your actual site dimensions.
How do I figure roof area for shingles and sheathing?
Multiply the plan (footprint) area, including overhangs, by the pitch multiplier. A 30 x 40 footprint with 1 ft overhangs is 32 x 42 = 1344 sq ft in plan; at 8/12 that is 1344 x 1.202 = 1616 sq ft - about 16.2 squares of shingles and roughly 51 sheets of plywood before waste. Add 10 to 15 percent waste for hips and valleys. The Roof Builder reports perimeter and area directly from your drawn footprint.
