Cuboid Diagonal Table: Space diagonal by Length
Reference table of space diagonal for Cuboid Diagonal across a range of length values — exact, engine-computed figures you can read off at a glance.
Cuboid Diagonal Calculator
Verified formula Updated Jun 2026 Private — runs on your device
Verified formula
Private
Space diagonal
13.0000
For general information only — not financial, tax, legal or medical advice. Verify before you rely on it.
How to use the Cuboid Diagonal Calculator
The Cuboid Diagonal Calculator works out your space diagonal in an instant. Enter length, width and height and the result updates as you type — it is free, needs no sign-up, and runs entirely in your browser so your figures stay private.
- Enter the length.
- Enter the width.
- Enter the height.
- Read off your space diagonal — the calculator updates automatically, with no button to press.
Formula
The Cuboid Diagonal Calculator uses the formula:
Space diagonal = √(Length ^ 2 + Width ^ 2 + Height ^ 2)
Worked example
For example, with length of 3 units, width of 4 units and height of 12 units, the space diagonal is 13.0000.
| Length | 3 units |
|---|---|
| Width | 4 units |
| Height | 12 units |
| Space diagonal | 13.0000 |
|---|
Results are estimates for educational use, not professional advice.
Frequently asked questions
Use d = √(l² + w² + h²). A 3 × 4 × 12 box has a space diagonal of exactly 13 units.
It is the longest straight line inside the box, running from one corner to the opposite corner through the interior.
It applies the Pythagorean theorem in three dimensions, extending √(a² + b²) to include the third edge.
An item fits if it is no longer than the space diagonal, which is why this is useful for packing long objects.
The Cuboid Diagonal Calculator uses the formula: Space diagonal = √(Length ^ 2 + Width ^ 2 + Height ^ 2). For example, with length of 3 units, width of 4 units and height of 12 units, the space diagonal is 13.0000.
Enter the length. Enter the width. Enter the height. Read off your space diagonal — the calculator updates automatically, with no button to press.
Related guides
How to Calculate Cuboid Diagonal: Formula, Steps & Examples
Learn how to calculate Cuboid Diagonal — the formula explained step by step, with worked examples and a free calculator to check your answer.