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Roof Truss Calculator — Quantities & Spacing
Calculate how many roof trusses you need based on building span and roof length. Standard 600mm centres for UK construction.
Width wall to wall — checks the chosen truss type can span it (count comes from roof length)
Length of building along the ridge
Counts the 2 end-position trusses (one per gable end) as gable trusses — they occupy the end positions, not added on top
Enter your supplier quote per truss
Centre-to-centre truss spacing (default 0.6 m)
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How We Calculate This
Our roof truss calculator determines the number of trusses needed based on your roof length and the standard 600mm spacing used in UK domestic construction. It also accounts for gable trusses at each end.
The formula
Total trusses = (Roof length ÷ 0.6m) + 1
Gable trusses = 2 (the two end positions, one per gable end)
Standard trusses = Total − Gable trusses
The +1 means the count includes a truss at each end of the roof, so a 10m roof gives (10 ÷ 0.6) + 1 = 18 total. The gable trusses occupy those two end positions rather than being added on top — they carry the gable wall — so 18 total is made up of 16 standard + 2 gable (per MiTek’s UK Trussed Rafter Handbook and Trussed Rafter Association guidance). For mono-pitch roofs only one gable truss is typically needed.
Truss types
- Fink (W): Most common domestic truss, suitable for spans up to ~11m. Internal W-shaped web members.
- Attic / Room-in-Roof: Designed to create usable space in the loft. Heavier and more expensive.
- Mono-Pitch: Single slope, used for lean-to extensions, porches and garages.
- Raised Tie: Bottom chord raised to give more headroom in the loft space, useful for storage.
Important notes
All trusses must be designed by a qualified truss manufacturer or structural engineer. They are made to order based on your specific span, pitch, loading (tile type, snow load, wind load) and any special requirements. This calculator gives an estimate of quantities only — always confirm with your truss supplier.
Frequently Asked Questions
The total number of trusses is calculated as: (Roof length ÷ 0.6m spacing) + 1, where the +1 accounts for the truss at the far end so there is one at each end position. For example, a 10m long roof needs (10 ÷ 0.6) + 1 = 16.67 + 1 = 17.67, rounded up to 18 trusses in total. Of these, the two end-position trusses are gable trusses (one per gable end), leaving 16 standard trusses, so 16 standard + 2 gable = 18 total. The gable trusses occupy the end positions rather than being added on top — they carry the gable wall, per MiTek's UK Trussed Rafter Handbook and Trussed Rafter Association guidance. Standard UK spacing is 600mm (2 feet) on centre.
The standard spacing for domestic roof trusses in the UK is 600mm (approximately 2 feet) centre to centre. This spacing works with standard plasterboard sheets (1200mm wide, supported on every other truss) and standard insulation rolls. Some designs may require 400mm spacing for heavier tile loads or longer spans.
A gable truss (also called a gable ladder or gable frame) sits at each gable end of the roof. It has a different design to standard trusses — usually a simplified frame with vertical studs instead of internal web members, designed to support the gable wall cladding and verge overhang. They are essential for a proper gable end finish.
Standard Fink (W) trusses can span up to about 11 metres for domestic loading in the UK. For wider spans, the truss design may need to be modified with additional web members, or an attic truss or steel beam may be more appropriate. All trusses should be designed and certified by a structural engineer or truss manufacturer to comply with Eurocode 5 (BS EN 1995-1-1), the current UK timber design standard since BS 5268-3 was withdrawn in 2018.
Roof truss prices vary significantly depending on the span, type and complexity. As a rough guide: standard Fink trusses for a 6-8m span typically cost £50-£100 each. Attic/room-in-roof trusses cost £150-£350 each due to their heavier construction. Prices also depend on delivery distance from the manufacturer. Always get a specific quote from a truss fabricator. For the rest of your roofing materials, use our Roof Tile Calculator and Felt and Batten Calculator.
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Last updated: February 2026
Verified against UK standards · estimates only, confirm with your supplier.