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Span chart (planning)
| Spacing | 2x6 | 2x8 | 2x10 | 2x12 |
|---|---|---|---|---|
| 12″ | 10.5 | 13.5 | 16.5 | 19.5 |
| 16″ | 9.5 | 12.0 | 15.0 | 18.0 |
| 24″ | 8.0 | 10.0 | 12.5 | 15.0 |
Note: This is a simplified planning tool. Confirm with official span tables and your inspector.
Maximum Deck Joist Spans by Size
The planning spans below reflect common assumptions (e.g., 40 psf live + 10 psf dead). Actual allowable spans vary by species, grade, treatment, and deflection criteria. For permitting, always use the span tables and handouts issued by your building department.
| Size | 12″ o.c. | 16″ o.c. | 24″ o.c. |
|---|---|---|---|
| 2×6 | ~10.5′ | ~9.5′ | ~8.0′ |
| 2×8 | ~13.5′ | ~12.0′ | ~10.0′ |
| 2×10 | ~16.5′ | ~15.0′ | ~12.5′ |
| 2×12 | ~19.5′ | ~18.0′ | ~15.0′ |
Load Calculations Explained
Live load is the variable weight from people and movable items; dead load includes the structure itself (framing, decking, fasteners). Hot tubs, planters filled with wet soil, and snow regions increase design loads. Use a conservative approach or consult a licensed professional for complex conditions.
Wood Species Strength Comparison
Species and grade determine bending strength and stiffness. Southern Yellow Pine and Douglas Fir‑Larch typically achieve longer spans than Hem‑Fir/SPF for the same joist size and spacing. When purchasing, match the span tables to the exact species, grade, and treatment stamps available at your yard.
When Spans Exceed Calculator Limits
If your target span exceeds planning values, consider one or more of the following:
- Reduce on‑center spacing (e.g., 16″ → 12″).
- Upsize joists (2×8 → 2×10) or switch to engineered/steel options per manufacturer guidance.
- Add an intermediate beam to shorten the span.
Next, review our deck beam size guide and deck joist span chart.
Maximum Spans by Joist Size
Use the calculator as a quick planning aid, then consult your jurisdiction’s official span tables. Spans depend on species, grade, treatment, spacing, and deflection criteria. Conservative choices improve comfort and reduce long-term maintenance from fastener fatigue.
- 2×6: Best for short spans, stairs, and tight layouts; often benefits from 12″ o.c.
- 2×8: Common residential choice for medium spans; 16″ o.c. is typical.
- 2×10: Longer spans at 16″ o.c.; excellent stiffness when paired with conservative spacing.
- 2×12: Longest spans in dimensional lumber; consider for large platforms and reduced bounce.
Load Calculation Methods
Determine loads from occupancy (live), structure (dead), and special cases (snow, wind, seismic, spas). Apply safety factors and check manufacturer literature for engineered or composite elements.
- Live Load: Often 40 psf for residential decks.
- Dead Load: Around 10 psf for framing, decking, and fasteners.
- Special Loads: Hot tubs, planters, outdoor kitchens—seek professional guidance.
Material Performance Data
Species/grade significantly affect bending strength (Fb) and stiffness (E). Southern Yellow Pine and Douglas Fir-Larch typically span farther than Hem-Fir/SPF for a given size and spacing. Moisture content and treatment also influence performance and fastener selection.
When Spans Exceed Calculator Limits
Options include tightening spacing, upsizing joists, switching to engineered/steel framing, or adding a beam to shorten spans. Coordinate with local officials early to avoid design iteration late in the process.
Legal Notice & Disclaimer
Planning tool only — not engineering or permitting advice. Results from these calculators are for educational and preliminary planning purposes. They do not replace stamped structural plans, professional engineering, manufacturer literature, or your building department’s adopted code and interpretations.
No warranties; use at your own risk. DeckJoistCalculator.com and its authors make no representations or warranties regarding accuracy, completeness, or fitness for a particular purpose. By using this site, you agree that you are solely responsible for design, permitting, construction methods, safety, and compliance, and you agree to hold DeckJoistCalculator.com, its owners, and contributors harmless from any claims, damages, or losses arising from your use of the information or tools provided.
Always verify final designs with your local building officials and consult a licensed professional for complex or unusual conditions (e.g., hot tubs, heavy planters, snow/wind/seismic requirements, multi-level framing, unusual materials).
Resources
Legal Notice & Disclaimer
Planning tool only. Results and charts on this site are simplified planning aids based on common assumptions. They are not a substitute for stamped engineering, permits, or inspections. Always confirm with local building officials and product manufacturers.
No warranties. This site is provided “as is,” without warranties of any kind. We disclaim liability for any loss or damage arising from its use.