Beam Span Reference
Continuous Span: Single Span × 1.2
Double Members (×90): Single Span × 1.4
Disclaimer: Indicative only. Always verify with AS 1684 span tables and consult an engineer.
Note: Spans shown assume normal domestic loading with load width up to 1.8m. Greater load widths may reduce allowable spans.
Beam Span Calculator — Timber Span Tables Australia
Australian residential construction uses over 4.2 million cubic metres of structural timber annually (ABARES, 2024). Getting your beam and joist spans right is critical — undersized members risk structural failure, while oversized members waste money. This calculator uses AS 1684.2 span table data to find maximum spans for floor joists, ceiling joists, rafters, bearers, verandah beams, and deck joists.
Maximum Span Table — Floor Joists (MGP10, Domestic Load)
| Timber Size | 450mm Spacing | 600mm Spacing |
|---|---|---|
| 90×45 | 1,600mm | 1,450mm |
| 120×45 | 2,150mm | 1,950mm |
| 140×45 | 2,500mm | 2,250mm |
| 190×45 | 3,350mm | 3,000mm |
| 240×45 | 4,250mm | 3,800mm |
| 290×45 | 5,100mm | 4,600mm |
Timber Stress Grade Factors
| Grade | Span Factor | Common Use |
|---|---|---|
| MGP10 | 1.0× | General framing, studs |
| MGP12 | 1.1× | Joists, rafters |
| MGP15 | 1.2× | Beams, lintels |
| F7 Hardwood | 1.05× | Basic hardwood framing |
| F14 Hardwood | 1.25× | Structural hardwood |
| F17 Hardwood | 1.35× | High-grade hardwood |
| LVL Engineered | 1.6× | Long spans, beams |
How the Calculation Works
The maximum span is determined by: Max Span = Base Span (from AS 1684.2 table) × Timber Grade Factor. For example, a 190×45 MGP12 floor joist at 450mm centres: 3,350mm × 1.1 = 3,685mm maximum span.
Frequently Asked Questions
What is the maximum span for a 190×45 floor joist?
Using MGP10 timber at 450mm centres, a 190×45 floor joist can span up to 3,350mm. At 600mm centres, the maximum reduces to 3,000mm. Higher grades like MGP12 or F14 increase the span.
What timber grade should I use for floor joists?
MGP10 is the most common for residential floor joists. MGP12 is used when longer spans are needed. For exposed applications, F17 hardwood or LVL provides greater spanning capacity.
Does stud spacing affect beam span?
Yes. Closer spacing (450mm) distributes load across more members, allowing longer spans. At 600mm centres, each member carries more load, reducing maximum span by 10–15%.
Do I need a structural engineer for beam sizing?
For standard residential construction, AS 1684.2 span tables are acceptable. For unusual loads, multi-storey buildings, or commercial applications, a structural engineer’s certification is required.
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