Joist and Beam Calculator

In construction, the joists and beams refer to a vital part of the structural system that transfers loads in floors, ceilings, and roof support. Smaller horizontal members are joists that usually are spaced closely together to support the floor or ceiling deck. Beams are structural members that are larger than joists and accept the load from the joist down to the foundation or other structural member. Proper sizing of the joists and beams in a building is critical to making sure that a building is safe, stable, and long-lived.

A joists and beam calculator is used by a contractor, engineer, or builder to determine the size and spacing between joists and beams to be used in specific building requirements. This process calculates load, span, material type, and local building codes in its calculations for the best-fitted specifications.

Joists and Beam Calculation Procedure

An accurate count and size of joists and beams in a structural system are necessary. The size of the beams and joists is decided after carefully analyzing the material’s properties, conditions, and deflection criteria. For precise calculations for accurate quantities of materials and thus costs of materials in tune with project requirements and budgets, utilizing material estimation can give you an exact amount and cost of materials needed for project management and budget adherence.

The following sections explain the core calculation principles and steps for determining the correct dimensions for your beam and joist.

Joists Calculation

They are horizontal framing members that support the flooring or ceiling material. Typical span is the distance between the walls or beams spaced regularly.

• Span length: Distance between the support where the joists rest
• Load: The weight that must be supported by each joist, which includes both live and dead loads.
• Material: Type of material for joists because it has a bearing on load capacity.
• Joist Spacing: Distance between joists, typically 16 inches on center for most residential construction.

Determine the Total Load per Square Foot

The total load per square foot is the sum of the live and dead loads.

Total load = 40 per square foot + 10 per square foot = 50 per square foot

Formula: To calculate the load per linear foot 

• Load per linear foot  = total load  × joist spacing
• 50psf x 1.33 feet = 66.5 pounds per line foot, signifying each joist will support 66.5 pounds per linear foot. 

Example: Assume that you are designing a floor system for a house subject to the following conditions:

• Span: 14 feet, the distance between the support for the joists.
• Load: 50 pounds per square pound of food for the dead load (building materials) and 40 pounds per square foot for the live load (people, furniture, etc.)
• Material: Softwood (for example, pine) with a strength of 1,400,000 psi
• Joists spacing 16 inches on the center

Application of The Bending Moment Formula

The bending moment M determines the force acting on the joist and calculates whether it will bend too much from the load. The formula of the bending moment is:  M = w x L2/ 8 

For Example: w= Load per linear foot(66.5 PLF) L = Span length (14 feet)

• M = 66.5 X (14 feet)2 / 8 + 1.629 foot-pound 

Section Modulus Requirement

This indicates the strength of a joist and its capacity to resist bending.

Formula: S = M/FB

Example: let’s suppose that 

• M= Bending moment (1,629 foot-pounds)
• FB = Allowable bending stress for Southern Pine (about 875 psi)

We first convert the bending moment into inches

• M = 1, 629 foot pound x 12 inches = 19, 548 inch pound

We now calculate the section modulus

• S = 19 548 inch pounds / 875 per square inch = 22.3 in3

Size Determination of The Joist

For this calculated value of the section modulus, you could determine the appropriate size of the joist. To check if the section modulus is adequate, we utilize a 2×10 Southern Pine joist.  

Calculation for Beams

Bemes sizing is complicated since beams carry loads from several joists, and the beam distributes these loads to walls or columns. It must be large enough to carry loads from all the joists. Calculating a beam’s proper size requires understanding its total load, span, and material strength.

Calculate the Total Load Supported by The Beam

You are tasked with installing a beam that will be carrying 12-foot joists. The beam you are tasked with has to cover a distance of 20 feet.

For Example : You have 4 joists, which carry 66.5 pounds per linear foot. The total load will fall on the beam.

• Total load from the joists: 4,000 pounds.
• Span of the Beam: 20 feet (the distance the beam will span).
• Material: Steel, which has a material strength factor of 50,000 psi

Apply the Beam Sizing Formula

The formula to calculate the beam size is: Beam size total load x span 2 / material strength factor

For Instance:

• Total load: 4000 pounds
• Span: 20 feet (convert to inches, 20 x 12= 240 inches)
• Material Strength Factor for Steel = 50,000 psi
• Beam size = 4,000 x (240)2 / 50,000 = 4,608

The above estimate indicates that the beam must carry a load of 4,608 pounds throughout 20 feet.

Final Result 

• Size of Joist: For a 14-foot span with 50 per square feet load, an acceptable joist size will be 2×10 Southern Pine joists spaced 16 inches in the center.
• Beam Size: For a 20-foot span, the beam must support 4,000 pounds. Considering the strength of the material, a steel I-beam would be used, depending on the size of a standard chart or structural engineer.

Frequently Asked Question

Q: Can I Also Input Data on Residential Buildings and Commercial Buildings? 

Yes, the calculator can be used for residential and commercial buildings, although some larger and more complex commercial structures might need specialized calculations. In that case, a call to a structural engineer is always wise.

Q: does the Calculator Adjust for Differences in Materials?

Most joist and beam calculators allowed the selection of materials for joists and beams, be it wood with a material like Southern Pine, steel, or engineered wood. Strength properties vary by type, and the calculator will size for your chosen material.