How far apart are roof trusses?

24 in on center is standard for wood trusses.

A Fink truss with W-shaped webs, the most common residential type.

Do I design trusses myself?

No — the truss manufacturer's engineer designs them for your loads.

Fink or scissor truss?

Fink is cheapest; scissor gives a vaulted ceiling.

How far can a wood truss span?

Up to about 40–50 ft for engineered wood trusses.

Can I use the attic space?

Not much with W-webs; use attic trusses or rafters for living space.

Roof truss calculator

Span, building length, pitch, overhang and spacing: you get the number of trusses, top and bottom chord lengths, truss height and estimated lumber.

Purchase quantity

21 unit

Net measurement: 21 unit

Trusses21 unit
Top chord with overhang16.306 ft
Bottom chord26.247 ft
Truss height6.135 ft
Lumber per truss (W-type estimate)79.429 ft
Total lumber1667.946 ft

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How it's calculated (visible formula)

trusses = ceil(length ÷ spacing) + 1; top chord = (span ÷ 2 + overhang) ÷ cos α; height = span ÷ 2 × tan α

Net geometric measurement, no waste.
Adjustable waste % for cuts and breakage.
Purchase rounded up to sellable units (boxes, bags, buckets, boards).

See methodology and formula versions

How to calculate it, step by step

Measure span and building length.
Set pitch and overhang.
Count trusses from spacing.
Work out top chord, bottom chord and height.
Order from the truss maker with these dimensions and loads.

Worked example: 26 × 40 ft building, 25°, 20 in overhang, 24 in OC

40 ft ÷ 2 ft = 20 + 1 = 21 trusses
Top chord: (13 + 1.6) ÷ cos 25° ≈ 16.3 ft
Height: 13 × tan 25° ≈ 6.1 ft

→ 21 trusses with 16.3 ft top chords and 26 ft bottom chords.

Common mistakes

Spacing trusses wider than the sheathing allows.
Skipping permanent lateral bracing.
Cutting or drilling engineered trusses.

Pro tips

Brace trusses during erection so they don't domino.
Install permanent bracing per the truss drawings.
Never cut or drill engineered truss members.
Tie every truss to the plate with hardware.

From calculation to quote

Add labour, overhead and your margin, and generate the professional PDF.

Create quote Calculate margin & VAT

FAQs

How far apart are roof trusses?: 24 in on center is standard for wood trusses.
What is a W truss?: A Fink truss with W-shaped webs, the most common residential type.
Do I design trusses myself?: No — the truss manufacturer's engineer designs them for your loads.
Fink or scissor truss?: Fink is cheapest; scissor gives a vaulted ceiling.
How far can a wood truss span?: Up to about 40–50 ft for engineered wood trusses.
Can I use the attic space?: Not much with W-webs; use attic trusses or rafters for living space.

Sources and standards

Maintained by Srikanta M · Formula v1.0.0 · Verified 2026-09-10 · Updated 2026-09-10 · Limits: quantity estimation, not structural design or site supervision.