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Calculate roof rafter length from span, rise, run, pitch, or angle. Live roof diagram, common pitch chart, and results in feet, inches, and meters — for framing, sheds, and home construction in the USA, UK & Canada.
Choose an input method — results update as you type.
Adjust span and rise with sliders — rafter length updates instantly.
Rafter length when 12 ft runClick a row to load.
| Pitch | Angle | Rise (12′ run) | Rafter length |
|---|
A roof rafter is the sloped framing member from the ridge to the wall plate. Its length is the hypotenuse of a right triangle formed by the rise (vertical height) and run (horizontal distance — half the building span for a simple gable roof).
Calculation: rafter length = square root of (rise² + run²). For example if 12 ft run and 6 ft rise → √(144 + 36) = 13.42 ft (about 13 ft 5 in). Add overhang separately if the rafter tail extends past the wall.
| Pitch | Rise | Rafter length | Typical use |
|---|---|---|---|
| 4/12 | 4 ft | 12.65 ft | Low slope, some ranch styles |
| 6/12 | 6 ft | 13.42 ft | Common residential |
| 8/12 | 8 ft | 14.42 ft | Steep residential |
| 10/12 | 10 ft | 15.62 ft | Very steep / snow country |
| 12/12 | 12 ft | 16.97 ft | 45° pitch |
Rafter length = √(rise² + run²), from the Pythagorean theorem on the roof triangle.
For a standard gable roof, run = span ÷ 2. A 24 ft wide building has a 12 ft run per rafter.
6/12 pitch ≈ 26.57°. Pitch: 6/12 (6″ rise for every 12″ run) Slope ratio: 6″ of vertical rise per 12″ of horizontal run. Every 12″ of horizontal distance results in a 6″ vertical rise.
This calculator finds the rafter from ridge to wall plate. Add tail length separately for eave overhang beyond the wall.
Run = 12 ft. √(12² + 6²) = 13.42 ft (13 ft 5 in approximately).
Rafters play a crucial role in roof construction. It uses to form the skeleton that supports your roof's weight and shape. This guide will walk you through every aspect of rafters, from their types to calculating rafter length, using tools like a rafter length calculator and understanding related costs.
Rafters are sloped structural beams that extend from the roof ridge or hip to the wall plate. Rafters are key components in creating a strong and durable roof structure.
Calculating rafter length is crucial for ensuring the stability and integrity of your roof. Here's a step-by-step guide:
Rafter Length = √(Run⊃2; + Rise⊃2;)You can calculate rafter length by multiplying the run by a roof pitch multiplier. Many tools, such as a roof rafter length calculator or a rafter length table, include these pitch multipliers to simplify the process.
A rafter length calculator is a handy tool that takes your roof’s pitch, span, and overhang measurements to compute the rafter length. Some calculators even account for a birdsmouth cut, which ensures a snug fit where the rafter meets the wall plate.
For smaller projects like sheds, you can use a shed rafter length calculator, which is tailored for simpler roof designs.
When it comes to larger roofing projects :
It includes features such as
Rafter Length = Run × Pitch MultiplierCalculating rafter length has never been easier. Building a shed, house, or complex structure rafter length calculator helps you instantly. These tools and techniques ensure precision and efficiency.
For best results, take advantage of free calculators available online, consider using a rafter length calculator with birdsmouth adjustments, and ensure you have accurate measurements for a durable and stable roof structure.