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Squareness Checker (3-4-5 Rule) 📐

Use the 3-4-5 rule (Pythagorean theorem) to verify if a corner is perfectly square (90 degrees) for foundations, framing, and layout work with instant accuracy feedback.

Squareness Checker (3-4-5 Rule) 📐
📐 The 3-4-5 Triangle Method
Side A (e.g., 3 ft) Side B (e.g., 4 ft) Diagonal (should be 5 ft) 90°
Formula: a² + b² = c² → 3² + 4² = 5² → 9 + 16 = 25 ✓
Enter Your Measurements
💡 Tip: We've pre-filled the classic 3-4-5 example. Adjust to match your actual measurements!
Measurement System: Choose your preferred units
Side A (First measurement along one wall):
Side B (Second measurement along other wall):
Diagonal (Actual measured diagonal):
Tolerance: Acceptable deviation from perfect square

Embed Squareness Checker (3-4-5 Rule) 📐 Widget

About Squareness Checker (3-4-5 Rule) 📐

Verify Perfect 90° Corners with the 3-4-5 Rule
Use the classic carpenter's method based on the Pythagorean theorem to check if any corner is perfectly square. Essential for foundations, framing, tile layout, and any construction project requiring precise right angles.
📐
Pythagorean Precision
Based on the mathematical principle a² + b² = c² to verify perfect 90-degree corners.
📏
Flexible Measurements
Works with any multiple of 3-4-5 (6-8-10, 9-12-15, etc.) and both imperial and metric units.
✓
Instant Feedback
Get immediate accuracy results with angle measurements and adjustment recommendations.

How to Use the 3-4-5 Rule

The 3-4-5 rule is a simple way to establish or verify a right angle using the Pythagorean theorem. Measure 3 units along one wall, 4 units along the perpendicular wall, and the diagonal between these points should measure exactly 5 units if the corner is square. You can scale this to any size: 6-8-10, 9-12-15, or even 30-40-50 feet for large foundations.

Step-by-Step Instructions

  • Step 1: Mark a point 3 feet (or meters) from the corner along the first wall (Side A).
  • Step 2: Mark a point 4 feet (or meters) from the corner along the second wall (Side B).
  • Step 3: Measure the diagonal distance between these two points.
  • Step 4: If the diagonal measures exactly 5 feet (or meters), your corner is perfectly square (90°).
  • Step 5: If not, adjust the corner until the diagonal matches the expected measurement.

Common Applications

Application Recommended Scale Typical Tolerance
Foundation Layout 9-12-15 ft or larger ±1/4 inch
Wall Framing 6-8-10 ft ±1/8 inch
Tile/Flooring Layout 3-4-5 ft ±1/16 inch
Deck/Patio 6-8-10 ft or larger ±1/4 inch
Fence Posts 3-4-5 ft ±1/4 inch

Why Squareness Matters

Ensuring corners are perfectly square is critical for structural integrity and aesthetics. Out-of-square corners can lead to gaps in tile, uneven floors, doors that won't close properly, and cumulative errors that become worse as you build outward. Starting with square corners saves time, materials, and rework.

Reference this content, page, or tool as:

"Squareness Checker (3-4-5 Rule) 📐" at https://MiniWebtool.com/squareness-checker/ from MiniWebtool, https://MiniWebtool.com/

by miniwebtool team. Updated: Nov 03, 2025

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