Beam Size Calculator
Calculate the required beam size for floor or deck loads. Enter span, tributary width, and load to get beam size recommendations with built-up options.
Beam Dimensions
Required Beam
(4) 2x10
Load Diagram
- Built-up beams: nail/bolt plies together per code (stagger joints)
- Support posts must be sized for total beam load
- Check point load capacity at beam supports
- For flush beams (joists hang from beam), use joist hangers
- Always verify with local building codes and engineering if uncertain
About This Calculator
The Beam Size Calculator determines the required beam dimensions to safely support floor joists, deck loads, roof rafters, or other structural applications—with options for built-up lumber beams, solid timber, and engineered lumber (LVL, PSL, Glulam). Whether you're framing a new floor, removing a load-bearing wall, building a deck, or sizing a ridge beam, this calculator accounts for span length, tributary width, and load conditions to give you code-compliant recommendations.
Beams are the horizontal structural members that collect loads from joists or rafters and transfer them to supporting posts, walls, or foundations. Proper sizing is critical: undersized beams can sag, crack drywall, cause doors to stick, and in severe cases fail catastrophically. Oversized beams waste material and add unnecessary cost. The IRC provides prescriptive span tables for common situations, while engineering calculations handle unusual loads or long spans.
Enter your beam span, tributary width, and load conditions to get instant recommendations for built-up beams (doubled or tripled 2x lumber), solid timber, and engineered lumber options. Our calculator includes 2026 material pricing, installation guidance, and alternative solutions when your span exceeds standard table values.
How to Use the Beam Size Calculator
- 1Enter the beam span—the distance between support posts or bearing walls.
- 2Enter the tributary width—the area of floor or roof the beam supports (typically half the joist span on each side).
- 3Select your load type: floor (40 PSF live + 10 PSF dead), deck (same), roof, or custom.
- 4Choose your preferred beam material: dimensional lumber, LVL, PSL, or Glulam.
- 5Review the recommended beam size and number of plies for built-up options.
- 6Compare alternatives if your first choice doesn't meet requirements.
- 7Switch to "Full Analysis" mode to adjust loads and see detailed calculations.
- 8Print or save your results for permit applications or contractor reference.
Understanding Tributary Width and Beam Loading
What is Tributary Width?
Tributary width is the floor or roof area that loads the beam. For a beam supporting floor joists:
| Measurement | How to Calculate |
|---|---|
| One-sided loading | Half the joist span on one side |
| Two-sided loading | Half the joist span on each side, added together |
| End beam (at wall) | Half the joist span on one side only |
| Interior beam | Half span from each side |
Tributary Width Example
Scenario: Center beam with joists spanning from exterior walls:
- Left side joists span 16 feet (wall to beam)
- Right side joists span 12 feet (beam to wall)
- Tributary width = (16 ÷ 2) + (12 ÷ 2) = 8 + 6 = 14 feet
Calculating Total Beam Load
The beam supports its tributary area multiplied by the load:
Total Load = Beam Span × Tributary Width × PSF Load
Example: 12-foot beam span, 14-foot tributary width, 50 PSF:
- Total load = 12 × 14 × 50 = 8,400 lbs
- Uniform load = 8,400 ÷ 12 = 700 lbs per linear foot
Standard Load Assumptions
| Application | Live Load | Dead Load | Total |
|---|---|---|---|
| Floor | 40 PSF | 10 PSF | 50 PSF |
| Deck | 40 PSF | 10 PSF | 50 PSF |
| Roof (light) | 20 PSF | 10 PSF | 30 PSF |
| Roof (snow) | 30-60 PSF | 15 PSF | 45-75 PSF |
| Balcony | 60 PSF | 10 PSF | 70 PSF |
Built-Up Beam Construction
What is a Built-Up Beam?
A built-up beam is created by fastening multiple 2x boards together. This allows you to build a strong beam from readily available lumber that's easier to handle than solid timber.
Standard Built-Up Beam Configurations
| Configuration | Total Width | Spacer | Application |
|---|---|---|---|
| 2-ply (two 2x boards) | 3" | None | Light loads, short spans |
| 2-ply with spacer | 3.5" | 1/2" plywood | Match 2x4 wall framing |
| 3-ply (three 2x boards) | 4.5" | None | Medium loads |
| 3-ply with spacers | 5.25" | Two 1/2" plywood | Match 2x6 wall framing |
Proper Assembly Method
Nailing pattern for built-up beams:
| Nail Size | Pattern | Spacing |
|---|---|---|
| 16d common | Staggered rows | 16" on center |
| Rows | 2 rows for 2-ply, 3 for 3-ply | Top, middle, bottom |
| Edge distance | 1-1/2" from edges | Both sides |
Assembly steps:
- Select straight, crown-matched lumber
- Apply construction adhesive between plies
- Nail in staggered pattern from both sides
- If splicing, stagger joints by at least 4 feet
- Splices must occur over support posts, not in span
Strength Comparison
| Beam Type | Relative Strength | Notes |
|---|---|---|
| Single 2x12 | 1.0× (baseline) | Rarely used for beams |
| (2) 2x12 | 2.0× | Most common built-up |
| (3) 2x12 | 3.0× | Heavy loads |
| (4) 2x12 | 4.0× | Very heavy, consider LVL |
IRC Beam Span Tables
Floor Beam Spans (40 PSF Live + 10 PSF Dead)
Southern Pine #2 Built-Up Beams:
| Beam Size | 6' Trib. | 8' Trib. | 10' Trib. | 12' Trib. |
|---|---|---|---|---|
| (2) 2x8 | 6'-2" | 5'-5" | 4'-10" | 4'-5" |
| (2) 2x10 | 7'-10" | 6'-10" | 6'-1" | 5'-7" |
| (2) 2x12 | 9'-6" | 8'-4" | 7'-5" | 6'-9" |
| (3) 2x8 | 7'-9" | 6'-9" | 6'-0" | 5'-6" |
| (3) 2x10 | 9'-9" | 8'-6" | 7'-7" | 6'-11" |
| (3) 2x12 | 11'-10" | 10'-4" | 9'-3" | 8'-5" |
Douglas Fir-Larch #2:
| Beam Size | 6' Trib. | 8' Trib. | 10' Trib. | 12' Trib. |
|---|---|---|---|---|
| (2) 2x8 | 5'-9" | 5'-0" | 4'-5" | 4'-1" |
| (2) 2x10 | 7'-3" | 6'-4" | 5'-8" | 5'-2" |
| (2) 2x12 | 8'-10" | 7'-8" | 6'-10" | 6'-3" |
| (3) 2x10 | 9'-1" | 7'-11" | 7'-1" | 6'-6" |
| (3) 2x12 | 11'-0" | 9'-8" | 8'-7" | 7'-10" |
Deck Beam Spans (IRC R507.5)
Southern Pine or Douglas Fir #2:
| Beam Size | 6' Joist Span | 8' Joist Span | 10' Joist Span |
|---|---|---|---|
| (2) 2x6 | 6'-1" | 5'-4" | 4'-9" |
| (2) 2x8 | 8'-1" | 7'-1" | 6'-4" |
| (2) 2x10 | 9'-8" | 8'-6" | 7'-7" |
| (2) 2x12 | 11'-6" | 10'-1" | 9'-0" |
| (3) 2x8 | 9'-8" | 8'-6" | 7'-7" |
| (3) 2x10 | 11'-6" | 10'-1" | 9'-0" |
| (3) 2x12 | 13'-6" | 11'-10" | 10'-7" |
Engineered Lumber Options
LVL (Laminated Veneer Lumber)
| Width | Depths Available | Max Span (typical) | Cost/LF |
|---|---|---|---|
| 1.75" | 7.25", 9.25", 11.25", 11.875", 14", 16", 18" | 20-32' | $4-12 |
| 3.5" (double) | Same | 24-36' | $8-24 |
| 5.25" (triple) | Same | 28-40' | $12-36 |
LVL advantages:
- Consistent strength (no knots affecting capacity)
- Longer spans than dimensional lumber
- Won't crown, twist, or warp
- Available in long lengths (up to 60')
PSL (Parallel Strand Lumber)
| Size | Max Span | Best For | Cost/LF |
|---|---|---|---|
| 3.5" × 9.25" | 16-20' | Headers, short beams | $10-18 |
| 3.5" × 11.875" | 18-24' | Floor beams | $14-24 |
| 5.25" × 11.875" | 22-28' | Long spans | $20-35 |
| 7" × 11.875" | 26-34' | Heavy loads | $28-45 |
PSL advantages:
- Higher capacity than LVL for same size
- Can be exposed (architectural appearance)
- Handles point loads better
Glulam (Glue-Laminated Timber)
| Width | Depth | Max Span | Applications |
|---|---|---|---|
| 3.125" | 9", 10.5", 12" | 16-22' | Residential |
| 5.125" | 9"-18" | 20-30' | Commercial/residential |
| 6.75" | 12"-24" | 28-45' | Commercial |
Glulam advantages:
- Can be curved or arched
- Attractive for exposed applications
- Available in very large sizes
- Multiple appearance grades
2026 Beam Pricing Guide
Current pricing for beam materials:
Dimensional Lumber (per linear foot):
| Size | Standard #2 | Select Structural |
|---|---|---|
| 2x8 | $1.10-1.60 | $1.80-2.40 |
| 2x10 | $1.50-2.20 | $2.50-3.50 |
| 2x12 | $2.00-3.00 | $3.50-5.00 |
| 4x6 | $2.50-3.50 | $4.00-6.00 |
| 4x8 | $4.00-5.50 | $6.50-9.00 |
| 4x10 | $5.50-7.50 | $9.00-13.00 |
| 4x12 | $7.00-10.00 | $12.00-18.00 |
| 6x6 | $4.50-6.50 | $8.00-12.00 |
| 6x8 | $7.00-10.00 | $12.00-18.00 |
| 6x10 | $10.00-14.00 | $17.00-25.00 |
Built-Up Beam Costs (materials only):
| Configuration | Cost/LF | 12' Beam | 16' Beam |
|---|---|---|---|
| (2) 2x10 | $3.00-4.40 | $36-53 | $48-70 |
| (2) 2x12 | $4.00-6.00 | $48-72 | $64-96 |
| (3) 2x10 | $4.50-6.60 | $54-79 | $72-106 |
| (3) 2x12 | $6.00-9.00 | $72-108 | $96-144 |
Engineered Lumber Pricing:
| Type | Size | Cost/LF | 16' Beam |
|---|---|---|---|
| LVL 1.75" | 9.25" deep | $5.50-7.00 | $88-112 |
| LVL 1.75" | 11.875" deep | $7.50-9.50 | $120-152 |
| LVL 1.75" | 14" deep | $9.00-12.00 | $144-192 |
| Double LVL | 11.875" deep | $15.00-19.00 | $240-304 |
| PSL 3.5" | 11.875" deep | $16.00-22.00 | $256-352 |
| Glulam 3.125" | 12" deep | $14.00-20.00 | $224-320 |
| Glulam 5.125" | 12" deep | $22.00-32.00 | $352-512 |
Note: Prices reflect 2026 market with Canadian lumber tariffs (35%) in effect.
Header Sizing for Wall Openings
What is a Header?
A header is a horizontal beam over windows, doors, or other openings in load-bearing walls. It transfers the load from above to the jack studs on each side.
Header Sizing Table (Single Story Above)
| Opening Width | Non-Load Bearing | Load Bearing |
|---|---|---|
| Up to 4' | (2) 2x4 | (2) 2x6 |
| 4' to 5' | (2) 2x4 | (2) 2x8 |
| 5' to 6' | (2) 2x6 | (2) 2x10 |
| 6' to 8' | (2) 2x8 | (2) 2x12 |
| 8' to 10' | (2) 2x10 | (3) 2x12 or LVL |
| 10' to 12' | (2) 2x12 | LVL required |
| Over 12' | Engineering required | Engineering required |
Header Sizing Table (Two Stories Above)
| Opening Width | Load Bearing |
|---|---|
| Up to 4' | (2) 2x10 |
| 4' to 6' | (2) 2x12 |
| 6' to 8' | (3) 2x12 or LVL |
| 8' to 10' | LVL 9.25" or larger |
| Over 10' | Engineering required |
Header Installation Requirements
| Component | Requirement |
|---|---|
| Jack studs | Minimum 2 per side (1 per side for non-load bearing) |
| Cripple studs | Above header to top plate |
| Nailing | Through king stud into header ends |
| Bearing | Header must rest fully on jack studs |
Post and Bearing Requirements
Post Sizing for Beam Support
| Load Carried | 4x4 Post | 6x6 Post |
|---|---|---|
| Up to 12,000 lbs | ✓ OK | Overkill |
| 12,000-17,000 lbs | Marginal | ✓ Recommended |
| 17,000-25,000 lbs | Not permitted | ✓ OK |
| Over 25,000 lbs | Engineering required | Engineering required |
Height also matters: Long posts may buckle. For heights over 10 feet, consider:
- 6x6 minimum for 10-14' heights
- 8x8 or engineered for taller applications
- Add bracing in both directions
Beam-to-Post Connections
| Connection Type | Load Capacity | Cost |
|---|---|---|
| Toenailing only | NOT RECOMMENDED | Low |
| Post cap (light) | 4,000-8,000 lbs | $8-15 |
| Post cap (heavy) | 8,000-16,000 lbs | $15-30 |
| Post cap (adjustable) | 12,000-20,000 lbs | $25-45 |
| Through-bolted | Depends on bolts | $5-15 |
| Welded steel bracket | 20,000+ lbs | $50-150 |
Post-to-Footing Requirements
| Post Location | Minimum Footing Size |
|---|---|
| Deck post | 16" × 16" × 8" deep |
| Interior floor post | 24" × 24" × 8" deep |
| Bearing wall above | Per engineering |
Critical: Posts must bear on concrete footings, not directly on soil. Footings must extend below frost line in cold climates.
When Standard Tables Don't Apply
Situations Requiring Structural Engineering
| Situation | Why Engineering is Needed |
|---|---|
| Spans over 14-16' | Exceed prescriptive table limits |
| Point loads | Tables assume distributed loads |
| Multiple stories above | Accumulated loads exceed tables |
| Unusual tributary widths | Tables have limited options |
| Cantilevers | Special calculations required |
| Seismic/high-wind zones | Additional load factors apply |
| Removing load-bearing walls | Must verify load path |
| Historic structures | Unknown existing conditions |
Getting Structural Engineering
| Service Type | Typical Cost | Turnaround |
|---|---|---|
| Pre-designed catalog beams | $0-50 | Instant |
| Standard beam calculation | $150-400 | 3-7 days |
| Beam + connection design | $300-800 | 5-10 days |
| Full structural plans | $1,000-5,000 | 2-4 weeks |
| Stamped engineering | +$100-300 | Same |
Alternatives to Large Beams
| Option | Application | Benefit |
|---|---|---|
| Steel I-beam | Very long spans | Smaller depth |
| Flitch plate | Upgrade existing beam | Adds capacity |
| Additional posts | Reduce beam span | Smaller beam works |
| Truss system | Open floor plans | Very long spans |
| Load-bearing wall | Alternative to beam | May simplify |
Installation Best Practices
Proper Beam Installation
| Step | Requirement | Purpose |
|---|---|---|
| 1. Verify bearing | Min 3" on posts, 1.5" on walls | Load transfer |
| 2. Check level | Shim posts, not beam | Proper load distribution |
| 3. Crown up | Orient crown toward load | Use natural bow |
| 4. Secure connections | Post caps or through-bolts | Prevent uplift/lateral |
| 5. Block at joists | Solid blocking at each end | Prevent rotation |
| 6. Check plumb | Posts must be plumb | Prevent eccentric loading |
Common Installation Errors
| Error | Problem | Solution |
|---|---|---|
| Insufficient bearing | Crushing, settlement | Minimum 3" on posts |
| No post caps | Beam can shift | Install proper hardware |
| Posts not plumb | Eccentric loading | Re-set posts plumb |
| Beam twisted | Uneven loading | Install crown up, block |
| Splices in span | Weak point | Splice only over posts |
| Wrong fasteners | Inadequate connection | Use structural hardware |
Flush Beam vs. Drop Beam
Flush beam (joists hang from beam with hangers):
- Pros: Maximum headroom, clean look
- Cons: Requires strong hangers, more complex
Drop beam (joists rest on top of beam):
- Pros: Simpler connection, easier framing
- Cons: Reduces headroom, beam visible
| Situation | Recommended |
|---|---|
| Basement with tight headroom | Flush beam |
| New construction | Either works |
| Retrofit | Usually drop beam easier |
| Deck | Drop beam standard |
Pro Tips
- 💡Always verify beam sizing with local building codes—some jurisdictions require engineered plans even for prescriptive table applications.
- 💡Support posts must bear on adequate concrete footings extending below frost line—never set posts directly on soil or floating slabs.
- 💡Use proper post caps and bases to connect beams to posts; toenailing alone is not code-compliant for structural connections.
- 💡For flush beams where joists hang from the side, use joist hangers rated for the load and install with all required fasteners.
- 💡When building multi-ply beams, stagger splices by at least 4 feet and ensure all splices occur directly over support posts.
- 💡Crown all beam lumber in the same direction (crown up) to prevent sagging; check for straight, dry lumber without excessive twist.
- 💡Consider headroom when sizing beams—a 14" deep beam in a basement may create clearance problems; LVL can provide the same strength in less depth.
- 💡For removing load-bearing walls, always install temporary shoring before cutting and leave it in place until the new beam is fully supported.
- 💡Allow 1/8" gap between beam ends and abutting surfaces for expansion; tight fits can cause buckling or cracking sounds.
- 💡Document your beam installation with photos before covering with drywall—inspectors may require this, and it helps with future modifications.
- 💡When splicing engineered lumber, follow manufacturer instructions exactly—improper splices void warranties and can fail.
- 💡For exposed beams, consider Glulam or wrapped LVL for appearance; raw LVL is not attractive and doesn't take stain well.
Frequently Asked Questions
Sandwich 1/2" plywood between two 2x boards to create a 3.5" wide beam that matches wall framing. Apply construction adhesive between plies, then nail with 16d nails in a staggered pattern at 16" on center from both sides. For 3-ply beams, use two plywood spacers or adhesive alone. All splices must occur over support posts—never splice in the middle of a span.
