`"Joist Count" = f( W , L , 16 )`

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The Floor Joist Count calculator  computes the number of joists (joists and end plates) required for a floor or deck based on the dimension of the room or deck and the on-center joist separation. 

Floor Joist Count Instructions

1. (W) -  Enter the width of the floor across the joists
2. (L) -  Enter the length of the floor parallel to the joists
3. (oC) - Enter the On-center Separation distance between joists

Floor Joist Board Count (JC): The Floor Joist Count calculator computes the total number of boards needed for the joists and end-plates combined.   The calculator also returns the number of joist hangers (ties) needed. 

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The Math / Science

The algorithm assumes a span (Floor Length) smaller than 20 feet for normal (solid wood) joists, because it is calculating the number of joists (lumber boards) using the lumber typically available up to 20 feet at the national suppliers (Lowe's, Home Depot & Menards).  It takes the width and calculates the number of joists needed to meet the on-center spacing requirement, and includes one for the beginning and an extra for any partial space.  The algorithm then calculates the number of end pieces (plates) needed based on the width and the joist lengths.  

The algorithm will calculate a joist length based on the required board length for the span (e.g. 20' board for an 18.5' joist/span).  It is important to note, that the strength of the joist and its width are driven by the use of the floor.  A free standing outside deck for some light furniture and a few people will have a different load requirement than a deck for a hot tub.  For this reason, this calculator does not tell you what boards to be used, just how many.  The most common driving factor in joist selection is the Live Load which is the specification for the load (weight) that is placed on a square foot of the floor.  Local building codes also dictate what joist boards can be used.   The live load will most commonly drive the Maximum Joist Span.

Once the floor joists are in place, then one needs to compute the:

• number of deck boards or the
• number of 4x8 sheets that go on the joists to make the floor. 

Building Calculators

• Total Building Materials Calculator

• Maximum Joist Span
• Area of a Roof
• Pitch of a Roof
• Number of Trusses Needed for a Roof
• 4x8s needed for a roof
• Shingles needed for a roof
• Number and Length of Metal Roof Panels
• Number and Length of Purlins
• Number and Length of Rafters
• Number and Length of Rafter and Collar ties

• Number and Length of wall top and bottom wall plates
• Number of Studs for a Room
• Number of Studs in a Wall
• Room Interior Area (wall and ceiling)
• Cubic Feet in a Room (volume)
• Number of 4x8 or 4x12 Sheets for a Room

• Number and Length of Floor Joists
• Number of Joist Hangers
• Compute the Cost of Floor Joists
• Compute iJoists for larger floors
• Compute the Number of 4x8 Sheets to cover the Deck or Floor
• Compute the number of Decking Boards to cover the deck or floor