Harth / Free tools
Framing & structure
Eight calculators for the framing questions that come up before a structural engineer or a span table is consulted: how far a floor joist or rafter can span, what size beam or header an opening needs, which LVL or glulam depth carries a load, how big a post must be, where a joist can be notched or drilled, how many hangers a floor takes, and how far a cross-laminated timber panel spans.
8 framing & structure tools
Free export on every toolFloor joist span calculator
Find the maximum floor joist span for a species, grade, size and spacing, with the bending, deflection and shear limits shown side by side.
Interactive tool · Free exportWood beam & header size calculator
Size a built-up 2x beam or header from its span and the floor or roof it carries, with moment, shear, reactions and every size and ply count checked.
Interactive tool · Free exportLVL & glulam beam calculator
Find the lightest LVL or glulam beam depth for a span and load, using typical published design values for each product.
Interactive tool · Free exportRafter length & span calculator
Work out common rafter length, overhang, stock length and rafter count from run and pitch, then check the rafter span for your size, species and roof load.
Interactive tool · Free exportJoist notch & hole calculator
Check a notch or bored hole in a sawn joist against the IRC depth, length, edge-distance and middle-third limits.
Interactive tool · Free exportWood post & column size calculator
Estimate the axial load a 4x4 to 8x8 wood post can carry with the NDS column stability factor, and the lightest size that works.
Interactive tool · Free exportJoist hanger & connector schedule
Count joist hangers and fasteners for every ledger, beam and header, and check each hanger's reaction against its catalogue rating.
Interactive tool · Free exportCLT floor panel span calculator
Estimate the maximum single span of a PRG 320 CLT floor panel from bending, shear, deflection and vibration, and the thinnest layup for your span.
Interactive tool · Free exportAbout the framing & structure tools
The span and sizing tools use published reference design values for common species and grades and the allowable stress method behind the American Wood Council span tables. Each one shows bending, deflection and shear separately, says which governs and lists every adjustment factor it applied, so you can follow the arithmetic. The notch and hole checker applies the residential code limits for sawn joists, and the CLT tool adds the vibration-controlled span that usually governs mass timber floors.
Imperial is the default, with feet, inches, psf and plf, and a metric switch converts every input and result. Results export as PDF or CSV with the inputs, factors and assumptions recorded.
These are preliminary estimates, not structural designs. They do not check point loads, connections, bearing, lateral bracing or local code amendments. Confirm sizes with the governing span tables, the manufacturer's literature or a structural engineer before you build.
Start with: Floor joist span calculator, Wood beam & header size calculator, Rafter length & span calculator.
Popular questions
How far can a 2x10 floor joist span?
A Douglas Fir-Larch No.2 2x10 at 16 in centres spans 15′-7″ under 40 psf live and 10 psf dead load at L/360, and 18′-0″ at 12 in centres. Other species, grades and loads change the figure.
From the Floor joist span calculator
What size header do I need for a 6 ft opening?
It depends on what the header carries. Under 8 ft of floor at 40 psf live and 10 psf dead, a single Douglas Fir-Larch No.2 2x12 passes on paper, and two plies fill a 2x4 wall. Under 8 ft of roof at 30 psf snow and 15 psf dead, a 2x10 passes.
From the Wood beam & header size calculator
What size LVL do I need for a 16 ft span?
Carrying 8 ft of floor at 40 psf live and 10 psf dead (400 plf), a two-ply 1¾ × 11⅞ in LVL 2.0E passes with typical values at 91% utilisation. Confirm with the manufacturer's tables.
From the LVL & glulam beam calculator
How do I calculate rafter length?
Multiply the horizontal run (less half the ridge thickness) by the slope factor √(1 + (rise/12)²), then add the overhang times the same factor. For a 12 ft run at 6:12 with an 18 in overhang and a 1½ in ridge, that is 15.02 ft.
From the Rafter length & span calculator
How big a hole can I drill in a 2x10 joist?
Up to one-third of the depth under IRC R502.8.1. A 2x10 is 9¼ in deep, so the maximum is 3.08 in, and the hole must stay at least 2 in from the top and bottom edges.
From the Joist notch & hole calculator
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