Reference · IBC 2024 Table 1604.3
Allowable deflection limits
Codes limit deflection as a fraction of span — L/360 means sag ≤ span ÷ 360. These are serviceability limits (cracking, bounce, finishes), checked against live load alone or total load depending on the row.
| Application | Limit | 12 ft allows | 20 ft allows |
|---|---|---|---|
| Floor, live load only | L/360 | 0.40 in (10.2 mm) | 0.667 in (16.9 mm) |
| Floor / roof, total (D+L) | L/240 | 0.60 in (15.2 mm) | 1.000 in (25.4 mm) |
| Tile / plaster / brittle | L/480 | 0.30 in (7.6 mm) | 0.500 in (12.7 mm) |
| Roof, no ceiling | L/180–L/120 | 0.80 in (20.3 mm) | 1.333 in (33.9 mm) |
| Masonry / glass walls | L/600 | 0.24 in (6.1 mm) | 0.400 in (10.2 mm) |
| Cantilever arm | L/180 | 0.80 in per 12ft arm | check at 2× length |
Live vs total — which governs?
Check both: L/360 under live load alone, L/240 under dead + live together. Light residential floors usually fail L/360 first; heavy roofs and long tile floors fail total-load or L/480 first. Tile manufacturers often demand L/720 — stricter than code.
Cantilever footnote
Some codes measure the cantilever limit against twice the arm length (a 10 ft arm checked as L = 20 ft → 1.333 in at L/180). The calculator reports the raw tip deflection and L/δ so you can apply either reading.