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What is the 3/4/5 rule in carpentry?
Answer: The 3-4-5 rule uses a right triangle (3×4×5) to create a perfect 90° layout line. Carpenters rely on it to square rooms, walls, decks, and tile before any cuts or fastening. In Myrtle Beach and the Grand Strand, Jordan Ross Construction pairs 3-4-5 with lasers so your cabinets, tile, and trim align perfectly.
Why square layout matters
Square layout prevents crooked backsplashes, door binds, uneven gaps, and “pinched” corners. We strike reference lines, check diagonals, and adjust framing before finish work begins. That way crown moulding lands tight, cabinet reveals are consistent, and tile edges finish cleanly.
How to apply the 3-4-5 rule on site
- Snap a baseline along the longest wall.
- From one point on the baseline, measure out 3 units and mark.
- From the same starting point, measure out 4 units roughly perpendicular and mark.
- Adjust the 4-unit line until the diagonal between the two marks reads exactly 5 units—now you’re at 90°.
- Extend both squared lines and use them as your layout references for framing, cabinets, or tile.
We typically scale the triangle (e.g., 6-8-10 or 9-12-15) for large rooms and verify with a laser before fastening.
Common uses of 3-4-5
- Cabinet installs: establish square reference lines before setting bases and uppers
- Framing: partitions, soffits, and closet walls for straight drywall and trim
- Decks & stairs: align joists and stringers for true treads and railings
- Tile layout: avoid slivers and keep grout joints consistent
Get layout-true carpentry
Straight lines at the start save time at the finish. Whether you’re planning built-ins, a feature wall, or a full remodel, we’ll square the space and sequence trades for an efficient, clean result. Book a layout-true site visit with Jordan Ross Construction.