Soffit and Fascia Calculator — Boards, Trims & Lengths

Our soffit and fascia calculator works out how many boards and trims you need based on your total eaves length, soffit depth and chosen board size. It covers both uPVC and timber options.

The formula

Fascia boards = Total eaves length ÷ Board length
Soffit boards = (Total eaves length ÷ Board length) × Rows needed

Soffit rows depend on your soffit depth vs. the standard 300mm board width. If your soffit is 250mm deep, one row of boards suffices. If it is 500mm, you will need two rows.

Standard UK sizes

• Fascia boards: 150-225mm wide, 18mm thick, lengths 2.5m/3m/5m
• Soffit boards: 300mm wide, 9mm thick, lengths 2.5m/3m/5m
• Joining trims: H-section connectors at every board joint
• Corner trims: Internal and external corner pieces

The joining-trims figure is an estimate: it assumes each fascia line is one continuous run and counts an H-section joint at every in-line board join. Where the eaves is broken at corners, some of those joins fall on the corner trims instead, so reduce the H-trim count accordingly and order corner pieces separately.

The calculator assumes 4 corner trims as standard. Adjust based on your roof shape — a semi-detached house may need fewer, while an L-shaped roof needs more. Always add 10% wastage for cuts and fitting adjustments.