Floor Joist Count

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

`(W)"Floor Width (the ends)"`

`(L)"Floor Length (span of joists)"`

`(oC)"On-center Separation"`

Floor Joist Count Instructions

(W) Width of Floor (across joists)
(L) Length or Span of Floor (parallel to joists)
(oC) 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 40 feet for normal (solid wood) joist or I-joists. It uses spans less than 40 feet for two reasons. First, it does not consider the use of a beam and overlapping joists. See the Joists on a Beam Calculator for spans over 40` or if on or more beams will be used. Second, because it is calculating the number of joists using the lumber typically available at the national suppliers (Lowe's, Home Depot & Menards). Menards carries I-joists up to 40' as of this writing . 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.

AS ALWAYS, CONFORM TO LOCAL BUILIDING CODES AND CONSULT PROFESSIONAL ENGINERING SPECIFICATIONS FOR ALL CONSTRUCTION AND DO NOT RELY SOLELY ON THESE CALCULATIONS. CONFIRM THEM WITH AUTHORITATIVE SOURCES!

Deck Builder Calculator provides estimates for a simple rectangular deck project. Calculator functions include the following:

Deck Board Count: Computes the number of decking boards needed for your deck based on the size of the deck and the size of the decking boards.
Deck Boards Cost: Computes the cost of deck board flooring based on a computed number of deck boards and the price per board.
Decking Cost Estimate: Estimates the cost of wood board decking based on total area and unit pricing in dollars per square feet.
Subfloor 4x8 Sheets: Computes the number of 4x8 sheets to cover floor/deck area.
Subfloor Cost: Computes the cost of 4x8 sheets to cover fool/deck area.
Deck Joist Count: Computes the number of floor joists needed for a deck. It returns the number of joists and plate boards, square feet of area and the length of the diagonal.
Joists on Beams: Computes the number of joists (2x dimensional lumber or i-joists), number of beams, number of joist hangers, and length of plate boards needed for a floor or deck with a span that might require one or more beams.
Deck Joist Cost: Computes the total cost of the floor joist boards.
Deck Stain and Sealer: Computes the amount of stain and sealer needed for a deck.

Joist Calculators

Floor Joist Count: Computes the number of joists (joists and end plates) and joist ties required for a floor or deck based on the dimension of the room or deck and the on-center joist separation.
Floor Joist Cost: Estimates the cost of Floor Joist boards (joists and end plates) required for a floor or deck based on the dimensions of the deck, spacing of joists and unit cost of joist boards.
Joist Hanger Count: Computes the number of joist hangers required for a deck based on the width of the deck and the spacing of joists.
I-Joist Count: Computes the the number of I-Joist boards required to cover a span (width) based on the size of the span and spacing of the I-Joists.
Maximum Joist Span: Computes the span length of a (1,200 pounds per square inch fiber stress) wood joist based on the live load, spacing, board width (e.g., 2x6 vs 2x10) and whether the joist need to be extra stiff for materials attached such as plaster below them.
Joists on Beams: Computes the number of joists (2x dimensional lumber or i-joists), number of beams, number of joist hangers, and length of plate boards needed for a floor or deck with a span that might require one or more beams.
On Center Spacing: Computes the even spacing between a number of objects (e.g. posts, studs, joists, rafters, trusses, lights, rebars) over a specified length or distance.