Beam Size Calculator

An advanced beam size calculator is a tool used in structural engineering and construction to determine the appropriate dimensions of beams for various building projects.

This calculator utilizes a specific formula that takes into account multiple factors to provide accurate and reliable beam size recommendations.

The core formula used in this is:

Required Beam Size = (Load × Span²) / (Wood Type Factor × Beam Type Factor)

Beam Size Calculation Formula

The fundamental equation used in this beam size calculator is:

Required Beam Size = (Load × Span²) / (Wood Type Factor × Beam Type Factor)

Where:

Required Beam Size is the cross-sectional area of the beam in square inches
Load is the total load on the beam in pounds per linear foot
Span is the length of the beam in feet
Wood Type Factor is a dimensionless coefficient based on wood species strength
Beam Type Factor is a dimensionless coefficient based on beam configuration

This formula simplifies the complex interactions between load, span, and material properties into a single, easy-to-use equation.

More Calculators:

How do I calculate what size beam I need?

To calculate the required beam size using this formula, follow these steps:

Determine the load: Calculate the total load the beam must support, including dead loads (permanent weight) and live loads (variable weight). Express this in pounds per linear foot.
Measure the span: Measure the distance between supports where the beam will be placed, in feet.
Choose the wood type: Select the wood species and identify its corresponding Wood Type Factor from standard tables.
Identify the beam type: Determine the beam configuration (e.g., simply supported, cantilever) and find the appropriate Beam Type Factor from engineering tables.
Apply the formula: Use the equation: Required Beam Size = (Load × Span²) / (Wood Type Factor × Beam Type Factor)
Interpret the result: The result will be in square inches. Choose a beam with a cross-sectional area equal to or greater than this value.
Verify code compliance: Ensure the chosen beam size meets local building code requirements.

What size beam do I need for a 16 foot span?

Load: 40 pounds per linear foot (plf)
Span: 16 feet
Wood Type: Douglas Fir-Larch (Wood Type Factor: 1200)
Beam Type: Simply supported (Beam Type Factor: 20)

Applying the formula:

Required Beam Size = (40 plf × 16² ft²) / (1200 × 20)
                   = 10,240 / 24,000
                   = 0.427 square inches

The closest standard lumber size that exceeds this area would be a 2×4 (actual dimensions 1.5″ x 3.5″ = 5.25 square inches).

In practice, a larger beam, such as a 2×8 or 2×10, might be more appropriate to meet all design criteria.

How to calculate the span of a beam?

While our formula focuses on calculating beam size, we can rearrange it to solve for the maximum span given a known beam size:

Span = √((Required Beam Size × Wood Type Factor × Beam Type Factor) / Load)

To use this:

Measure the beam’s cross-sectional area in square inches.
Identify the Wood Type Factor for the beam material.
Determine the Beam Type Factor based on support conditions.
Estimate the expected load in pounds per linear foot.
Apply the rearranged formula to calculate the maximum span.

How to calculate steel beam size?

Our formula is primarily designed for wood beams. For steel beams, a modified version of the formula could be used:

Required Steel Beam Size = (Load × Span²) / (Steel Grade Factor × Beam Type Factor)

The process would be similar to wood beams, but with different factors:

Determine design loads and span.
Choose steel grade and identify its corresponding Steel Grade Factor.
Identify the Beam Type Factor based on support conditions.
Apply the formula to calculate the required steel beam size.
Select a standard steel section that meets or exceeds the calculated size.
Verify deflection and shear capacity using additional calculations or software.

Beam Size Calculation Chart

We’ll assume Douglas Fir-Larch wood (Wood Type Factor: 1200) and simply supported conditions (Beam Type Factor: 20) for all examples.

Span (ft)	Load (plf)	Calculated Beam Size (sq in)	Closest Standard Size
10	30	0.125	2×4 (5.25 sq in)
12	40	0.288	2×4 (5.25 sq in)
16	50	0.533	2×6 (8.25 sq in)
20	60	1.000	2×8 (11.25 sq in)
24	70	1.680	2×10 (15.25 sq in)

Beam Size Calculator – Calculate Size of Beam