Diagonal Calculator – Calculate Diagonal of Rectangle or Square

Need to find the diagonal of a rectangle, square, or triangle? This Diagonal Calculator is your go-to tool for quick, accurate results. Whether it's for screen measurements, geometry, or construction, our calculator helps you save time and avoid manual math.

Just input the dimensions, and get instant results using the correct diagonal formula every time!

What is a Diagonal Calculator?

A Diagonal Calculator is a simple online tool that helps you calculate the diagonal of a rectangle or square using height and width. It's perfect for:

✅ Finding screen sizes (TVs, monitors, mobile devices)
✅ Furniture and window design
✅ Construction or interior layout measurements
✅ Geometry and math projects

Using this calculator removes the need for manual math. Just enter the width and height, and you’re done!

How to Calculate Diagonal of Rectangle

The formula for calculating the diagonal of a rectangle is:

Diagonal (d) = √(width² + height²)

Where:

Width = Horizontal side of the rectangle
Height = Vertical side of the rectangle
Diagonal = The line connecting opposite corners

This is also known as the diagonal of rectangle formula, and it's based on the Pythagorean Theorem.

How to Use This Diagonal Calculator?

1️⃣ Enter the Width (e.g., 12 cm)
2️⃣ Enter the Height (e.g., 5 cm)
3️⃣ Click 'Calculate' – Your diagonal result appears instantly!

It’s fast, easy, and perfect for accurate measurements.

Example Calculation

Let’s say your rectangle is 12 cm wide and 5 cm tall:

Diagonal = √(12² + 5²) = √(144 + 25) = √169 = 13 cm

So, the diagonal length is 13 cm.

Using Diagonal Formula for Square

If you have a square, use this diagonal of square formula:

Diagonal = side × √2

For example, if each side is 10 cm: Diagonal = 10 × √2 ≈ 14.14 cm

Why Use a Diagonal Calculator?

🔹 No need to remember formulas
🔹 Quick and accurate results
🔹 Ideal for comparing dimensions
🔹 Works for both rectangles and squares
🔹 Perfect for geometry students and professionals

Other Related Tools

🔸 Diagonal Matrix Calculator – For advanced math problems involving matrices
🔸 Calculate Triangle Diagonal – Useful for scalene or isosceles triangle sides

Factors That Affect Diagonal Length

✔️ Width and Height – Larger values mean longer diagonals
✔️ Unit Consistency – Always use the same unit (inches, cm, mm)
✔️ Precision – Choose decimals if you need accurate technical measurements
✔️ Application – Construction, screen sizes, and design accuracy matter

Use this calculator to explore multiple combinations and see how different measurements affect the diagonal.

FAQs

A Diagonal Calculator is a tool that helps you calculate the length of the diagonal of a rectangle or square using the Pythagorean theorem. You input the length and width, and it calculates the diagonal.

It uses the formula √(length² + width²) to calculate the diagonal of a rectangle or square. Just enter the values for length and width, and the tool does the math instantly.

You need to enter:

Length: The length of the rectangle or square.
Width: The width of the rectangle or square.

No, this calculator is specifically designed for rectangles and squares. For other shapes like triangles or polygons, different formulas are needed.

Yes, the diagonal length is calculated in the same unit as the input values. If you enter length and width in meters, the result will be in meters.

No, the calculator works directly in your web browser. You don’t need to download or install any software.

Yes, the calculator supports decimal inputs for precise measurements and returns an accurate diagonal length.

Yes, the Diagonal Calculator is completely free to use without any login or registration required.