Beam Span Calculator

Determine required beam size from span, load, and wood species.

By Konstantin Iakovlev · Updated April 2026 · Source: HomeAdvisor

ft
lbs/sqft
ft

Recommended Size

2x10

Total Load

2,880.00 lbs

Max Spans — SPF

2x810 ft max
2x1013 ft max
2x1216 ft max

Use the Beam Span Calculator above to calculate your results. Enter your values and see instant results — all calculations run in your browser.

Disclaimer: This calculator is for informational purposes only and does not constitute tax, financial, or legal advice. Results are estimates based on the information you provide and current rates. Always consult a qualified tax professional or financial advisor for advice specific to your situation.

How It Works

Sizing a beam comes down to three things working together: how far it has to span, how much load it carries, and which wood species you're framing with. Feed those in and you get a beam dimension that holds up structurally and squares with 2026 building codes, so the project clears inspection instead of turning into an expensive, possibly dangerous fix.

Behind the numbers are the engineering formulas set out in the American Wood Council's (AWC) National Design Specification (NDS) for Wood Construction. The required section modulus (Sx) handles bending while the moment of inertia (Ix) governs deflection, and both are checked against the published properties of common dimensional lumber across a range of species.

Load is the input to scrutinize hardest, because lowballing it is what turns into a sagging or failed beam down the line. Treat the result as a floor rather than a target, too: it's the minimum size that works, and your local code or a stiffer floor feel may call for going up a dimension for extra margin.

Example: Deck Joist Calculation

  1. 1 Input: You're building a deck with a 12-foot (3.66m) span, supporting a total live and dead load of 60 pounds per square foot (psf) (2.87 kPa), and using Southern Pine No. 2 grade lumber.
  2. 2 Calculation: The calculator processes these inputs, determines the required bending strength and stiffness based on NDS 2026 tables for Southern Pine No. 2, and iterates through standard dimensional lumber sizes (e.g., 2x8, 2x10, 2x12) to find the smallest beam that meets both criteria.
  3. 3 Result: The calculator determines that a 2x10 Southern Pine No. 2 joist spaced at 16 inches on center (40.64 cm o.c.) is sufficient for the specified span and load, satisfying both bending and deflection limits.
  4. 4 Context: This result means that using 2x10 joists at 16 inches on center will safely support your deck's anticipated load without excessive sagging. You should still verify this against local building codes, which may have specific requirements for deck construction.

Source: HomeAdvisor · Last updated: April 2026

Frequently Asked Questions

How far can a 2x10 beam span without support?
A doubled 2x10 (two boards nailed together) in Douglas Fir can typically span 8-10 feet carrying a floor load. An engineered LVL beam of the same depth can span further. Actual capacity depends on wood species, grade, load, and spacing of supports.
What is the difference between a beam and a joist?
A beam is a primary structural member that carries loads from joists, walls, or other beams to columns or foundations. Joists are smaller repetitive members that span between beams and directly support the floor or ceiling deck.
When do I need an engineered beam instead of dimensional lumber?
Engineered beams (LVL, PSL, or glulam) are needed when spans exceed what dimensional lumber can handle, typically beyond 10-12 feet. They offer higher strength, more consistent quality, and are available in longer lengths than solid lumber.

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