Roof Overhang Calculator
Reviewed by the My Roof Pitch editorial team · Updated · Free, no sign-up, works offline after first load
A roof overhang's sloped tail length equals the horizontal overhang divided by the cosine of the roof angle. For a 12 in horizontal overhang at a 6:12 pitch (26.57°), the tail is about 13.4 in, the fascia drops about 6 in, and a 150 ft perimeter adds roughly 167 sq ft of extra roof and soffit area.
Key takeaways
- Tail length is always longer than the horizontal overhang once pitch is factored in.
- Fascia drop increases with steeper pitch for the same overhang.
- Overhang adds roof area around the whole eave perimeter — include it in material orders.
- Soffit area scales directly with the horizontal overhang width.
Your measurements
Enter the values you know — results update live.
Horizontal distance the roof extends past the exterior wall, measured level.
Rise per 12 inches of run.
Total length of eave edge receiving this overhang.
Analysis
Live results from your measurements.
Show the working
- Roof angle:
atan(6 ÷ 12)= 26.57° - Tail length:
12 ÷ cos(angle)= 13.42 in - Fascia drop:
12 × tan(angle)= 6 in - Soffit area:
(12 ÷ 12) × 150= 150 sq ft - Added roof area:
(13.42 ÷ 12) × 150= 167.7 sq ft
What this calculator does
A roof overhang is the horizontal distance a roof extends past the exterior wall at the eave, protecting siding and windows from rain and sun. Because the roof is sloped, the actual rafter tail is longer than the horizontal overhang, and the fascia board at the end of the tail sits lower than the wall top plate by an amount tied to the pitch. This calculator turns a horizontal overhang and pitch into the real sloped tail length, the fascia drop, the soffit area to be boxed in, and the extra roof area the overhang adds around the whole perimeter.
How to use it
- Decide the horizontal overhang distance you want past the wall, typically 12 to 24 inches.
- Enter the roof pitch as rise per 12 inches of run.
- Enter the total eave perimeter receiving this overhang.
- Read the sloped tail length to size rafter tails or ladder framing.
- Use the fascia drop to set the fascia board height below the top plate.
- Use soffit area and added roof area to order soffit panels and extra shingles or panels.
The formula
Tail length
tail length = horizontal overhang / cos(roof angle)
Converts the level overhang measurement into the actual sloped rafter tail length.
Fascia drop
fascia drop = horizontal overhang × tan(roof angle)
How far below the wall top plate the fascia board sits at a given pitch.
Worked example
12 in horizontal overhang, 6:12 pitch, 150 ft eave perimeter.
- Angle: atan(6 ÷ 12) = 26.57°
- Tail length: 12 ÷ cos(26.57°) = 13.42 in
- Fascia drop: 12 × tan(26.57°) = 6.00 in
- Soffit area: (12 ÷ 12) × 150 = 150 sq ft
- Added roof area: (13.42 ÷ 12) × 150 = 167.7 sq ft
A 12 in overhang at a 6:12 pitch needs a 13.4 in rafter tail, drops the fascia 6 in, and adds about 168 sq ft of roof and 150 sq ft of soffit.
Tail length and fascia drop for a 12 in overhang by pitch
| Pitch | Tail length | Fascia drop |
|---|---|---|
| 3:12 | 12.5 in | 3.0 in |
| 6:12 | 13.4 in | 6.0 in |
| 9:12 | 15.0 in | 9.0 in |
| 12:12 | 17.0 in | 12.0 in |
Common mistakes
- Using the horizontal overhang as the rafter tail length without converting for pitch.
- Forgetting the fascia drops lower at steeper pitches, misaligning gutters.
- Not accounting for added roof area when ordering shingles or panels, running short on material.
- Ignoring soffit venting requirements when sizing the soffit area.
- Mixing up overhang measured from the wall versus from the ridge line.
Assumptions and limits
- Overhang is measured horizontally from the exterior wall face.
- Pitch is uniform along the entire eave perimeter being calculated.
- Soffit area assumes a level soffit at the horizontal overhang width.
- Added roof area does not include gable rake overhangs, only eave overhangs.
Frequently asked questions
What is a typical roof overhang size?
Most homes use a 12 to 24 inch horizontal overhang at the eaves, though wider overhangs are common in rainy or sunny climates for extra wall protection.
Why is the rafter tail longer than the overhang?
Because the roof slopes, the rafter travels along the hypotenuse of a triangle whose horizontal leg is the overhang, making the actual board length longer by a factor of 1/cos(angle).
How do I calculate fascia drop?
Multiply the horizontal overhang by the tangent of the roof angle; this tells you how far below the wall top plate the fascia board sits.
Does a bigger overhang need more shingles?
Yes. The overhang adds roof area around the entire perimeter, which should be included in material takeoffs along with waste allowance.
What is the difference between overhang and eave?
The eave is the lower edge of the roof where it meets the wall; the overhang is the horizontal distance that edge extends past the wall.
How does pitch affect overhang framing?
Steeper pitches need longer rafter tails and a bigger fascia drop for the same horizontal overhang, and may need deeper ladder framing at gable ends.
Should overhang be the same on all sides?
Eave overhangs and gable rake overhangs are often different dimensions; this calculator covers the eave (sloped) side specifically.
Does overhang affect soffit vent sizing?
Yes, a wider overhang gives more soffit area, which can accommodate more net free vent area for attic ventilation.
Last updated 2026-10-08. Results are estimates for planning and are not a substitute for a licensed engineer or local code review.