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Soffit Calculator

A soffit calculator works out the soffit area and panel quantity for your eaves, plus the fascia length to match — from the run length and how far the roof overhangs the wall. Soffit and fascia close in the underside of the eaves and let the attic ventilate.

Your measurements

Result

The area is simply the eave length times the overhang width, but it's easy to forget the fascia (same length as the eaves) and the ventilation. This covers all three so the order is complete.

How it is calculated

Soffit area = eave length × overhang width, plus 10% waste for cuts. Fascia length equals the eave length. Vent guidance uses roughly one standard soffit vent per 150 sq ft of soffit as a starting point — balance attic intake (soffit) with exhaust (ridge) per code.

Steps

Enter the total eave/run length.
Enter the overhang width (wall to fascia).
Choose whether to include fascia.
Read the soffit square footage and panel area.
Add vented soffit or separate vents for attic airflow.

Worked example

120 ft of eaves with an 18 in overhang is about 180 sq ft of soffit (≈198 with waste), 120 ft of fascia and ~2 vents' worth of airflow.

Common questions

How much soffit do I need?

Eave length × overhang width, plus waste. 120 ft of eaves with an 18 in overhang is about 180 sq ft.

How much fascia do I need?

Fascia runs along the eaves, so it equals your eave length — here, 120 ft.

Do I need vented soffit?

Usually yes — vented soffit (or added soffit vents) feeds attic intake air, working with ridge or gable exhaust to prevent moisture and heat build-up.

How do I measure overhang?

Measure horizontally from the wall to the outer edge of the fascia; that width times the eave length is the soffit area.