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Floor joist span calculator for wood

Calculator presetASD, NDS 2024

Design a wood floor joist in Calcs.com. Start from the Floor Joist preset, set your size and span, and check bending, shear, bearing and deflection to NDS 2024.

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How floor joist design works in Calcs.com

The Floor Joist preset sets up the Wood Beam (ASD, NDS 2024) calculator in Calcs.com, a standards-aligned calculation platform for structural engineers.

[ 01 ]

Start from the Floor Joist preset

Choose Wood Beam (ASD), then Floor Joist. You start from the member you're designing, with its loads and limits in place, rather than a blank beam. Floor Joist sets up the common indoor case: a level, dry floor joist with floor loads over its spacing. Each value below is where the preset starts. You can change any of them.

  • Loads

    Starts with Floor Load: dead 10 psf, live 40 psf, over a 16 in spacing. Change any value or the spacing, or add line, point and moment loads.

  • Deflection limits

    Starts at L/360 for live load and L/240 long term. Set the limits your project calls for.

  • Service condition

    Starts dry. Set it to wet for a member that stays damp, which usually means exterior work.

  • Member and bracing

    Starts as a repeating member, top braced for lateral torsional buckling. Change the plies or the bracing to match your framing.

Wood Beam (ASD) presets in Calcs.com, with Floor Joist picked

[ 02 ]

Change it to your floor joist

Pick a size and grade from the standard sections database, enter a custom section, or let Autosize choose one. Then set the plies, span, supports and bracing.

  • Size and grade

    Standard lumber, glulam, LVL, PSL and LSL sections, or a custom section, with Autosize beside the size field.

  • Span and supports

    Plan length, support type, position and bearing length for each support.

  • Bracing and flitch plates

    Continuous bracing for lateral torsional buckling, and optional flitch plates.

The Floor Joist preset in Calcs.com: a 2x10 D.Fir-L No. 1 from the standard sections database, with Autosize, 14 ft span

[ 03 ]

See every check as you design

Bending, shear and bearing utilization sit at the top of the sheet. Deflection is checked against the limits the preset sets.

A Floor Joist sheet in the Calcs.com Wood Beam (ASD) calculator, with its bending, shear and bearing utilization

Try the floor joist preset: change the size and span

Pick a size and a span. The sheet shows what the Wood Beam (ASD, NDS 2024) calculator returned for that floor joist.

  • Utilization at a glance

    Bending, shear and bearing as percentages at the top of the sheet, as in the calculator.

  • Deflection against the preset's limits

    Live load and long-term deflection checked against L/360 and L/240.

  • Every check, as the calculator prints it

    Moment, shear and bearing utilization and both deflections, with the value behind each percentage.

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Wood Beam (ASD, NDS 2024) - Floor JoistSavedJ1
Bending76%Shear29%Bearing17%

Key Properties

Size and Grade
Number of Plies =
Beam Plan Length =ft
Center-to-Center Spacing (= tributary width) =in
Distributed LoadsFloor Load: dead 10 psf, live 40 psf
Continuous Bracing for Lateral Torsional Buckling
Service ConditionDryWet

Checks

Moment Utilization =1712 lb-ft / 2255 lb-ft76%
Shear Utilization =489 lb / 1665 lb29%
Bearing Utilization =489 lb / 2812 lb17%
Governing Live / Short-Term Deflection =-0.274 in (L/613)59%
Governing Long-Term Deflection =-0.317 in (L/531)45%

Plies, spacing, loads and bracing are as the Floor Joist preset sets them. Every input is editable in the calculator. This sheet replays 12 solves by the Calcs.com engine on 2026-11-12: 3 sizes by 4 spans. In the calculator, any size, span, spacing or load is solved the same way.

Floor joist span table: 2x8 to 2x12

Each cell is the Floor Joist preset solved in the Wood Beam (ASD, NDS 2024) calculator at that size and span, with every other input as the preset sets it. It shows the governing check's ratio. Above 1.00 fails.

Floor joist span table, governing check ratio by member and span
Member12 ft14 ft16 ft18 ft
2x80.82BendingPasses1.22Live load deflectionFails1.82Live load deflectionFails2.59Live load deflectionFails
2x100.56BendingPasses0.76BendingPasses0.99BendingPasses1.25BendingFails
2x120.42BendingPasses0.57BendingPasses0.74BendingPasses0.94BendingPasses

13 presets on one wood beam calculator

Each member preset, from Floor Joist to Deck Beam, sets up the same calculator with its own loads and deflection limits. Rafter and Hip / Valley put the member on a slope. Deck Joist and Deck Beam set wet service.

Open the Floor Joist preset in the calculator

  1. [ 01 ]Start your free trial. You land on the app's home page.
  2. [ 02 ]Open the Wood Beam (ASD) calculator for the edition you design to.
  3. [ 03 ]Choose Floor Joist from its presets. Its values load in, ready to change.
See the full Wood Beam (ASD, NDS 2024) calculator
Edition

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Pick the edition you design to. The sheet and the steps above follow it, and each edition has a Floor Joist preset.

These results use the preset's loads and limits. Check every input against your project before you rely on a result. The engineer of record stays responsible for the design.

Frequently asked questions

Design your floor joist in Calcs.com

Start from the Floor Joist preset and check your size and span to NDS 2024.

Design your floor joistSee the full Wood Beam (ASD, NDS 2024) calculator
Linking a calculation to a column in Calcs.com, with the AISC Steel Construction Manual reference attached

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