How this calculator works
Soffit is the panel that closes the underside of the eaves. The area is the length of the eaves times the depth of the overhang. Panels run parallel to the wall, so you count how many rows of panel it takes to cross the overhang (the width of the overhang divided by the width of a panel, rounded up), then how many panels it takes to run the length of the eaves in each row.
Worked example: 120 ft of eaves with a 16 in overhang is 160 ft² (1.6 squares). With 12 in panels that is 2 rows, so 22 panels of 12 ft with 10% waste. With 16 in panels it is 11, and a 24 in overhang with 12 in panels needs 22. The J-channel or F-channel is 22 pieces of 12 ft.
Assumptions and sources
- Assumptions used: 10% waste added; panels run parallel to the wall and are cut to fit the last row; one run of channel on the wall side and one on the fascia side.
- Vinyl soffit comes in 12 ft lengths (12 ft 6 in for some makers) and in 8, 12 and 16 in widths, solid or vented. Many makers run the panels from the wall to the fascia for a short overhang, which uses less and needs no seam, so ask which suits your product. Vented panels give the attic intake air, which you can size with the attic ventilation calculator. Corner pieces, trim for the fascia and nails are extra.
The formula and a worked example are shown above, so you can check any result by hand. Read how we calculate and check our numbers. Results are estimates for planning: supplier products vary, so check the size printed on the label.
Soffit panels for common overhangs
120 ft of eaves, 12 ft long panels, 10% waste.
| Overhang | 8 in panels | 12 in panels | 16 in panels | Area |
|---|---|---|---|---|
| 12 in | 22 | 11 | 11 | 120 ft² |
| 16 in | 22 | 22 | 11 | 160 ft² |
| 18 in | 33 | 22 | 22 | 180 ft² |
| 24 in | 33 | 22 | 22 | 240 ft² |
Tips before you buy
- Measure the overhang in two places on each side of the house: the depth often changes where the roof was extended.
- Panels run parallel to the wall and are cut so that the last one fits. Let the panel move: do not nail it tight, and leave a gap at the channel for expansion.
- Vented soffit supplies the intake for the attic. Do not paint over or cover the vents, and keep the baffles clear of insulation.
- Fit the F-channel or J-channel to the wall first, then the fascia, then slide the panels in.
- Aluminum and vinyl soffit are cheap compared with the work of replacing a rotted board, so check the lookouts and the fascia for rot while the old soffit is off.
Tools & materials for this project
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Frequently asked questions
How much soffit do I need?
Multiply the length of the eaves by the depth of the overhang. 120 ft of eaves with a 16 in overhang is 160 ft², which is 22 panels of 12 ft by 12 in wide, with 10% waste.
How long and wide are vinyl soffit panels?
Usually 12 ft long (12 ft 6 in for some makers) and 8, 12 or 16 inches wide, solid or vented. A 12 in panel is often three 4 in strips.
Do I need J-channel or F-channel for soffit?
Yes. One run goes on the wall side and one on the fascia side to hold the panels, so you need about twice the length of the eaves.
How many squares of soffit do I need?
A square is 100 ft². 160 ft² is 1.6 squares.
Should I buy vented or solid soffit?
Vented soffit is the usual choice because the attic needs intake air. Use the attic ventilation calculator to check that the vent area is enough.
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Related calculators & guides
Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.