Contractor Job Estimator
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BuyIRC Joist Span Tables
Species × size × spacing grids from IRC 2021 — bookmarkable reference, still a starting point
These grids are the same cells the joist span calculator returns. Floor values are IRC 2021 Table R502.3.1(2) for residential living areas (40 psf live / 10 psf dead, L/360, No. 2). Deck values are IRC 2021 Table R507.6 for 40 psf live load, No. 2, wet service, no cantilever. They are not local law by themselves.
How to use a cell: guide. Floor vs deck: comparison. Existing bounce: troubleshooting.
Look up one combination.Floor or deck, species, size, spacing.
Open Calculator →Floor Joists — IRC 2021 Table R502.3.1(2)
Residential living areas. No. 2 grade. 40 psf live / 10 psf dead. L/360. Dry service. Spans in feet-inches.
IRC 2021 Table R502.3.1(2) — Floor joists — residential living areas. 40 psf live load; 10 psf dead load; L/360; No. 2. Dry service (interior floor)
| Species / grade | Size | 12" o.c. | 16" o.c. | 24" o.c. |
|---|---|---|---|---|
| Southern Pine #2 | 2x6 | 10′-3″ | 9′-4″ | 7′-7″ |
| 2x8 | 13′-6″ | 11′-10″ | 9′-8″ | |
| 2x10 | 16′-2″ | 14′-0″ | 11′-5″ | |
| 2x12 | 19′-1″ | 16′-6″ | 13′-6″ | |
| Douglas Fir-Larch #2 | 2x6 | 10′-9″ | 9′-9″ | 8′-3″ |
| 2x8 | 14′-2″ | 12′-9″ | 10′-5″ | |
| 2x10 | 18′-0″ | 15′-7″ | 12′-9″ | |
| 2x12 | 20′-11″ | 18′-1″ | 14′-9″ | |
| Hem-Fir #2 | 2x6 | 10′-0″ | 9′-1″ | 7′-11″ |
| 2x8 | 13′-2″ | 12′-0″ | 10′-2″ | |
| 2x10 | 16′-10″ | 15′-2″ | 12′-5″ | |
| 2x12 | 20′-4″ | 17′-7″ | 14′-4″ | |
| Spruce-Pine-Fir #2 | 2x6 | 10′-3″ | 9′-4″ | 8′-1″ |
| 2x8 | 13′-6″ | 12′-3″ | 10′-3″ | |
| 2x10 | 17′-3″ | 15′-5″ | 12′-7″ | |
| 2x12 | 20′-7″ | 17′-10″ | 14′-7″ |
Deck Joists — IRC 2021 Table R507.6
40 psf live load row. No. 2 grade. Wet service. No cantilever. DF-L, Hem-Fir, and SPF share one IRC row.
IRC 2021 Table R507.6 — Deck joists — 40 psf live load, no cantilever. 40 psf live load (snow not concurrent); 10 psf dead load; L/360 at main span; No. 2, wet service factor included. Wet service. DF-L / Hem-Fir / SPF include incising factor and share one IRC row.
| Species / grade | Size | 12" o.c. | 16" o.c. | 24" o.c. |
|---|---|---|---|---|
| Southern Pine #2 | 2x6 | 9′-11″ | 9′-0″ | 7′-7″ |
| 2x8 | 13′-1″ | 11′-10″ | 9′-8″ | |
| 2x10 | 16′-2″ | 14′-0″ | 11′-5″ | |
| 2x12 | 18′-0″ | 16′-6″ | 13′-6″ | |
| Douglas Fir-Larch #2 | 2x6 | 9′-6″ | 8′-4″ | 6′-10″ |
| 2x8 | 12′-6″ | 11′-1″ | 9′-1″ | |
| 2x10 | 15′-8″ | 13′-7″ | 11′-1″ | |
| 2x12 | 18′-0″ | 15′-9″ | 12′-10″ | |
| Hem-Fir #2 | 2x6 | 9′-6″ | 8′-4″ | 6′-10″ |
| 2x8 | 12′-6″ | 11′-1″ | 9′-1″ | |
| 2x10 | 15′-8″ | 13′-7″ | 11′-1″ | |
| 2x12 | 18′-0″ | 15′-9″ | 12′-10″ | |
| Spruce-Pine-Fir #2 | 2x6 | 9′-6″ | 8′-4″ | 6′-10″ |
| 2x8 | 12′-6″ | 11′-1″ | 9′-1″ | |
| 2x10 | 15′-8″ | 13′-7″ | 11′-1″ | |
| 2x12 | 18′-0″ | 15′-9″ | 12′-10″ |
Source and Limits
Values transcribed from IRC 2021 Table R502.3.1(2) and IRC 2021 Table R507.6 as published in the Massachusetts Residential Code, 10th edition (IRC 2021 based) on UpCodes. Floor Table R502.3.1(2) was cross-checked against the 2021 Seattle Residential Code Chapter 5 PDF (same IRC 2021 table). No values were interpolated or rounded off the published feet-inches.
Not included: sleeping-area 30 psf table, 20 psf dead-load columns, 19.2" o.c., Select Structural / #1 / #3 floor rows, deck snow-load rows, or cantilever columns. Those are real IRC rows — they are just not this chart. If your job needs them, open the adopted code or the AWC span calculator, or hire a licensed engineer.
Citation: 2021 International Residential Code Tables R502.3.1(2) and R507.6; Massachusetts Residential Code, 10th edition (UpCodes); 2021 Seattle Residential Code Chapter 5 PDF for floor-table cross-check.
One combination, not the whole grid?Use the calculator. The yellow starting-point flag is on the result.
Open Calculator →FAQ
Why bookmark this instead of only the calculator?
Because a crew comparing three sizes at two spacings wants the grid. The calculator is for one cell. Both are starting points.
Why do DF-L, Hem-Fir, and SPF match on the deck grid?
Because Table R507.6 prints them as one row. The floor grid prints them separately. That is the code, not a simplification we invented.
Can I use these numbers as the permit documents?
No. Attach the adopted local tables or engineering. This page is a reference to the 2021 IRC cells listed above.
Any trade
Checkout opens here — you stay on this page.
Framing Layout Gear
Confirm the stamp and the bay. Then layout. The table does not replace a square or a level on an existing sag.
16×24 Framing Square
Mark joist layout after the table says the size reaches. Same square for the deck stairs off that frame.
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Swanson Speed Square
Quick 90s and crown checks. The calculator still wants species and grade from the stamp, not from memory.
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48" Box Beam Level
Existing bounce and sag are a field measurement first. Compare that to the tabulated span second.
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7-1/4" Circular Saw
Do not cut a joist longer than the table allows and hope. Change size, spacing, or get engineering.
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Johnson Stair Gauges
When the deck also needs stairs, lock the square. Span and stringer math are separate.
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Look Up the Table Cell
Species, size, spacing, floor or deck. Starting point only — verify local code and the stamp.
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