Posted on Date Posted by Dipak Patel on 27th Aug 2025
What Is the 3/4/5 Rule for Tiling (and Why It Matters)?
What Is the 3/4/5 Rule for Tiling (and Why It Matters)?
What Is the 3/4/5 Rule?
The 3/4/5 rule is a simple way to create a true right angle using tape measures and a chalk line—no maths degree needed. It’s a practical version of the Pythagorean theorem: if one side measures 3 units, the adjacent side 4 units, then the diagonal between those points should measure 5 units if the angle is exactly 90°.
Why It Matters for Tiling
Tiles highlight crooked walls and drifting lines. Starting square prevents joint creep (gaps getting wider across a room), keeps feature patterns aligned, and protects you from awkward slivers at edges.
Step‑by‑Step: Setting Out with 3/4/5
- Find your baseline. Choose the longest, straightest wall. Snap a chalk line parallel to it to act as your reference.
- Mark 3 and 4. From the starting corner on your baseline, measure 3 units (e.g., 3m) and mark it. From the same corner along your perpendicular line, measure 4 units (e.g., 4m) and mark.
- Check the diagonal. Measure the diagonal between the two marks. If it’s exactly 5 units (e.g., 5m), your corner is square. If not, adjust the perpendicular line until the diagonal reads 5.
- Scale up as needed. For bigger areas, use 6/8/10 or 9/12/15 to increase accuracy.
Where to Use It
- Floors: Large spaces where drift is noticeable.
- Walls: When a feature wall or running bond must be dead straight.
- Herringbone: Getting the launch angle wrong makes the whole pattern look off.
Balancing Cuts and Sightlines
Once square, dry‑lay a few rows to check how cuts fall at doorways, baths, and thresholds. Shift your starting line slightly to avoid thin slivers. Remember that walls in older homes won’t be perfectly square—trust your layout lines more than the plaster.
Before you mix adhesive, make sure you have the right consumables: tile spacers, quality adhesive and colour‑matched grout. Next‑day delivery available.
Pro Tips
- Use a laser if you have one, but always verify with a tape and 3/4/5.
- Snap layout lines for both directions so rows and columns have guides.
- Check for flatness as well as squareness—no layout can correct a wavy floor.
Bottom Line
Spending 10 minutes on the 3/4/5 method prevents hours of rework. Square lines are the foundation of a professional‑looking tile installation.