Floor Joist and Rafter Calculator

Estimated spans, rafter length and birdsmouth cut.

Project Details
Enter your measurements and requirements
Results
Calculated estimates for your project
Estimated span limit15 ft 4 in
Span needed14 ft 0 in
Span checkWithin this estimate. Have it confirmed before you build
Members16 2x10
Checked againstIRC 2021 R301.7, not yet reviewed by a licensed professional

Turn these numbers into a build plan.

  • 15 ft 4 in estimated limit
  • 14 ft 0 in needed
  • 16 2x10 members
Materials List
Recommended materials and quantities
2x10 lumber16

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Project plan · built from your numbers

Frame floor joists, 14 ft span

2x10 members at 16 in on center. Estimated limit 15 ft 4 in against 14 ft 0 in needed.

Materials
$358
Time
2 weekends
Level
Advanced
5 steps 4 tools 3 materials
  1. 1

    Check the design

    These spans are estimates. Have your building department or an engineer confirm them.

  2. 2

    Lay out

    Mark 16 in centers on the bearing members.

  3. 3

    Crown and cut

    Sight each joist and set every crown up.

01 · Your numbers
Estimated limit
15 ft 4 in
Needed
14 ft 0 in
Members
16 2x10
02 · The plan

5 steps · 4 tools · 3 materials

2 more steps, the full tool list and a shopping list you can check off as you go.

03 · Finished

Your plan is 60% built. Save it.

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Frame floor joists, 14 ft span

Finished in 2 weekends · $358 DIY

Built for your estimated limit of 15 ft 4 in. Your first plan saves free. No card needed.

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How joist and rafter spans are estimated

These are calculated estimates checked against published rules that no licensed reviewer has signed off here, so confirm them with your building department. See the framing guide and roof pitch conversions.

  1. Pick the lumber. Species, grade, size and spacing all change the span.
  2. Set the load. Floors use a live load by room type. Roofs use your snow or roof live load.
  3. Compare limits. The span is the shorter of what bending and deflection allow.
  4. Cut rafters. Rafter length is the run plus overhang, times the slope factor.

Estimated floor joist spans at 16 in on center

Calculated for a 40 psf live and 10 psf dead load, deflection limited to span / 360. Not code table values.
Species2x62x82x102x12
Spruce-pine-fir No. 29 ft 3 in12 ft 3 in15 ft 4 in17 ft 10 in
Douglas fir-larch No. 29 ft 8 in12 ft 9 in15 ft 7 in18 ft 1 in
Hem-fir No. 29 ft 1 in11 ft 11 in15 ft 1 in17 ft 7 in
Southern pine No. 29 ft 3 in11 ft 9 in14 ft 0 in16 ft 6 in

Frequently asked questions

How far can a 2x10 joist span?

At 16 in on center under a 40 psf living load, No. 2 spruce-pine-fir estimates at about 15 ft 4 in here. Species, grade and spacing change that, and your local tables decide.

Is this a span table from the building code?

No. The spans are calculated from beam formulas and published lumber values, which can differ slightly from printed tables.

How deep can a birdsmouth cut be?

A common guide is no more than a quarter of the rafter depth. The calculator warns you when a cut goes deeper.

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