Truss Load Calculator

Multiply the area load (psf) by the joint's tributary area: the panel length along the top chord times the truss spacing on center. A roof carrying 10 psf dead plus 20 psf snow on a truss spaced 24 in. o.c. with 4 ft panels gives 4 × 2 = 8 sq ft per joint, so each top-chord joint carries 30 × 8 = 240 lb = 0.24 kip downward. End joints carry half of that because their tributary width is halved. The converter at the top of this page runs exactly this arithmetic, and the deep-linked models let you check the member forces that follow.

A distributed load (psf) is how roofing weight arrives — spread over the roof plane. A point load (kip or lb) is how a truss analysis needs it — concentrated at the joints. The bridge between them is tributary area: each panel point 'owns' half of each adjacent panel. A pin-jointed analysis treats members as two-force members, so load applied in the middle of a member would add bending that the model cannot represent; converting the distributed load to joint point loads is not a shortcut but a requirement for the model to be valid.

Dead load: 10–15 psf covers shingles, sheathing, and the truss itself for ordinary residential roofs. Roof live load: 20 psf is the standard maintenance case on horizontal projection. Snow load: use your local ground snow value — roughly 0–10 psf in the Gulf South, 20–30 psf across the Midwest, 40–50 psf in New England, and 70+ psf in mountain towns — reduced by about 0.7 for flat-roof conditions. The authoritative numbers come from your building department or the IRC/ASCE 7 tables for your jurisdiction; these figures are starting points for planning, not stamped design values.

Under pure gravity roof load, the bottom chord carries no direct applied load — its force comes from resisting the outward spread of the top chords as tension. That changes when anything hangs from it: attic storage, a ceiling of drywall (5–8 psf), mechanical equipment, or a room-in-truss floor. Each 1 psf applied to the bottom chord behaves like a floor load case and can raise bottom-chord tension by a third or more at common spans. Model bottom-chord loads explicitly at the bottom-chord nodes whenever storage or finishes are planned.

No. Interior top-chord joints carry a full panel's tributary area; the eave (heel) joints and — depending on layout — the ridge carry reduced tributary areas, typically half. On a Fink truss with uniform panels, heel joints get half the interior point load because they own only one side of framing. Loading every joint equally overstates the total by roughly one panel's worth and skews reactions; the deep-link example on this page applies equal loads for a clean hand check, then you can refine the heels to half values for a production run.

A load table gives you psf values; a truss loading calculator turns them into the numbers your structure actually experiences — point forces per joint, and the member forces and reactions that follow. This page's converter produces the per-joint Fy values, and the Structural Analysis tab they deep-link into shows how those loads distribute into compression in the top chords, tension in the bottom chord, and alternating forces in the webs — including reactions that you can verify by summing the applied loads by hand.