Arch Calculator

Calculate the properties of a circular arch, such as radius, angle, and length, from its span and rise.

Updated: November 2025 • Free Tool

Arch Calculator

Results

Arch Radius
0
Arch Angle 0°
Arch Length 0
Area 0
Perimeter 0

What is an Arch Calculator?

An Arch Calculator is a free construction tool that helps you determine the key dimensions of a circular arch. It calculates the arch's radius, angle, length, area, and perimeter based on its span (width) and rise (height). This tool is indispensable for a variety of users, from professional architects and builders to DIY enthusiasts undertaking home improvement projects. By simply inputting the two basic measurements of span and rise, users can instantly obtain the detailed geometric properties required for accurate planning and construction.

This calculator is useful for:

  • Architects and Designers - for designing structures with arches, ensuring aesthetic appeal and structural integrity.
  • Builders and Contractors - for constructing arches with accurate dimensions, minimizing material waste and ensuring a precise fit.
  • DIY Enthusiasts - for home projects involving arched openings, such as doorways, windows, or garden structures.
  • Students - for learning about the geometric properties of arches and applying mathematical formulas in a practical context.

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For building stairs, try our Stair Calculator to get the dimensions for risers, treads, and stringers.

To estimate materials for wall construction, check our Framing Calculator to determine the number of studs and plates needed.

How This Arch Calculator Works

The calculation is based on the geometric properties of a circular segment. The formulas used are:

Radius (R) = (Span² + 4 × Rise²) / (8 × Rise)
Angle (θ) = 2 × arcsin(Span / (2 × R))
Arch Length (L) = R × θ (θ in radians)
Area (A) = (R² / 2) * (θ - sin(θ))
Perimeter (P) = L + Span

Where:

  • Span = The width of the arch.
  • Rise = The height of the arch.
  • Radius = The radius of the circle of which the arch is a part.
  • Angle (θ) = The central angle of the arch.
  • Arch Length (L) = The length of the curved part of the arch.
  • Area (A) = The area of the segment enclosed by the arch and the span.
  • Perimeter (P) = The total length of the arch and the span.

Key Concepts Explained

Span

The span is the horizontal distance between the two points where the arch begins. It is the primary measurement that defines the width of the opening or structure.

Rise

The rise, also known as the height, is the vertical distance from the midpoint of the span to the highest point of the arch. The rise determines the arch's curvature.

Radius

For a circular arch, the radius is the distance from the center of the circle to any point on the arch. A larger radius results in a flatter arch, while a smaller radius creates a more pronounced curve.

Arch Length

The arch length is the distance along the curve of the arch. This measurement is crucial for determining the amount of material needed for the arch itself.

How to Use This Calculator

1

Enter Span

Input the total width of the arch. Ensure the measurement is accurate for precise results.

2

Enter Rise

Input the height of the arch from the center of the span. This value must be less than or equal to half of the span.

3

Get Results

The calculator will instantly provide the radius, angle, arch length, area, and perimeter of the arch.

Benefits of Using This Calculator

  • •
    Accuracy: By using precise mathematical formulas, the calculator eliminates the guesswork and potential for human error in complex geometric calculations.
  • •
    Efficiency: Instantly obtain all the necessary dimensions without the need for manual calculations or complex drawings, saving valuable time in the planning phase.
  • •
    Material Estimation: The calculated arch length and area help in accurately estimating the amount of materials required, reducing waste and controlling project costs.
  • •
    Versatility: The calculator can be used for a wide range of applications, from small decorative arches to large structural elements.

Factors That Affect Your Results

1. Span and Rise Accuracy

The precision of the calculated dimensions is directly dependent on the accuracy of the input span and rise measurements. Double-check your measurements before using the calculator.

2. Measurement Units

Ensure that both the span and rise are entered in the same unit of measurement (e.g., inches, feet, meters). The results will be in the same unit.

3. Arch Type

This calculator is designed for circular (segmental) arches. The formulas will not be accurate for other types of arches, such as elliptical or parabolic arches.

Arch Calculator - Free online calculator to calculate arch dimensions with instant results and detailed breakdown
Professional calculator interface for calculating arch dimensions. Features include real-time calculations, detailed results, and mobile-friendly design.

Frequently Asked Questions (FAQ)

Q: What is an arch calculator?

A: An arch calculator is a tool used to determine the dimensions of an arch, such as its radius, angle, and length, based on its span and rise.

Q: What is the span of an arch?

A: The span is the horizontal distance between the two ends of the arch.

Q: What is the rise of an arch?

A: The rise is the vertical distance from the baseline to the highest point of the arch.

Q: What unit of measurement should I use?

A: You can use any unit of measurement (e.g., feet, meters, inches), as long as you are consistent for both the span and rise.