Sizu Home › Calculators › Squaring & the Diagonal Check
Enter the case width and height and your two diagonal measurements, then press Calculate.
From the book — Chapter 3. Expected diagonal = √(w² + h²) (Pythagoras). Lean ≈ difference × diagonal ÷ (2 × width) — the rule Chapter 3 derives and checks against the exact trig.
The lean rule is accurate to well under a hundredth of an inch for ordinary cabinet sizes. Everything stays in your browser — no sign-up, nothing stored.