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Circular, Semi-Circular & Sector Plot Area Calculator

Calculate the area of a circular, semi-circular, or sector-shaped plot using the radius and, for a sector, the central angle. Enter measurements in your preferred length unit and get the calculated area in your selected square-area unit.

Calculate Circular, Semi-Circular & Sector Land Area

Select the plot shape and enter the required measurements to calculate the land area using the selected length and area units.

Circular land plot showing radiusA circular land plot with a radius measurement from the centre to the edge.Radius = 10 mCIRCULAR LAND PLOTArea = π × Radius²Radius measured from centre to boundary
Land area = π × Radius × Radius
Current unit: Metres (m)
Circular Land Area
314.15926536
m²
π × 10 m × 10 m = 314.15926536 m²

Circular, Semi-Circular & Sector Plot Area Formulas

The correct area formula depends on the shape of the plot. A complete circle uses the radius of the circle, a semi-circle is half of a circle, and a sector uses both the radius and its central angle.

Circular Plot: Area = π × r²

Semi-Circular Plot: Area = ½ × π × r²

Sector Plot: Area = (θ ÷ 360) × π × r²

Here, r represents the radius and θ represents the central angle of the sector in degrees. The radius and angle should describe the actual plot geometry being measured.

How to Calculate Circular Plot Area

  1. Measure the radius from the centre to the circular boundary.
  2. Choose the length unit used for the measurement.
  3. For a complete circle, use the circular plot mode.
  4. For a half-circle, use the semi-circular plot mode and enter the radius.
  5. For a sector, enter both the radius and the central angle in degrees.
  6. Select the desired square-area unit and calculate the result.

Measuring a Circular or Sector-Shaped Land Plot

For a circular plot, the radius is measured from the approximate centre of the plot to its boundary. For a semi-circular plot, measure from the centre of the diameter to the curved boundary. For a sector, identify the centre and measure the radius along each boundary line while determining the angle between those radius lines.

Measurements should be taken carefully because small errors in radius can produce a larger difference in calculated area, particularly for larger plots.

Important Land Measurement Note

This calculator provides a mathematical area calculation from the measurements entered by the user. Actual land boundaries may not form a perfect circle, semi-circle, or sector. For official land records, registration, boundary disputes, or legal purposes, verify measurements using the applicable survey or official land records.

Common Measurement Mistakes

  • Entering diameter when the calculator requires radius.
  • Using different length units for different measurements.
  • Entering a sector angle greater than 360°.
  • Estimating an irregular boundary as a perfect circle without verification.
  • Using calculated area as an official land-record measurement without verification.

Frequently Asked Questions

What measurement does this calculator require?

All three modes require the radius. The sector mode also requires the central angle in degrees.

Can I calculate a full circle using the sector option?

Yes. A sector with a central angle of 360° represents a full circle and produces the same mathematical area as the circular plot calculation.

Can I enter measurements in feet or metres?

Yes. The calculator supports metres, feet, yards, inches, centimetres, and millimetres for length measurements and corresponding square-area units for the result.

Is this suitable for official land records?

The calculator is intended for mathematical area estimation from entered dimensions. Official land records and legal measurements should be verified through the applicable survey or land-record authority.