About Annulus Area Calculator
This annulus area calculator subtracts the inner circle from the outer one: A = π(R² − r²). Use it for washers, pipes in cross section and ring-shaped paths. It is free, needs no sign-up and runs in your browser, so nothing you enter is uploaded.
Radii 10 and 6 give π × 64, about 201.06. The outer radius must be larger than the inner one.
How to use Annulus Area Calculator
- Choose the shape from the list.
- Type its dimensions, such as length and width or radius. The labels in each box name the measurement.
- Pick the unit you measured in, and the unit you want the area converted to.
- Read the area, the converted value and the table of every unit.
- Compare your shape with the labelled diagram to make sure each number is the right measurement.
- Open the step-by-step working to see the formula with your numbers in it.
Features
- Eleven shapes, each with formula, working and diagram.
- Eight length units for the inputs, from millimetres to miles.
- Result converted to square metres, feet, yards, kilometres, miles, acres and hectares.
- Bangladesh land units: decimal (shotangsho), katha and bigha.
- Perimeter or circumference where the inputs allow it.
- Regular polygon for any number of sides from 3 to 1000.
- Sector area from the angle in degrees, annulus from outer and inner radius.
- Clear errors, such as an inner radius larger than the outer one.
Annulus area
The difference of two circle areas.
A = π (R² − r²)Worked examples
R = 10, r = 6 gives 201.0619 square units
π × (100 − 36).
Privacy: how it works
- All calculations run in your browser tab. The measurements you enter are not sent to Ulkaa or to any other server, and there is nothing to sign in to.
Tips
- Measure everything in the same unit before you enter it, or set the unit selector to match.
- The height of a triangle, trapezoid or parallelogram is the perpendicular distance, not the slanted side.
- For an L-shaped room, split it into two rectangles, find each area and add them.
- A rhombus needs its two diagonals, not its side length.
Frequently asked questions
Is it really free?
Yes. There is no price, no trial and no credit card. Ulkaa Tool does the work with your own device, so there is no server bill to pass on to you.
Do I need an account?
No. There is no sign-up and no login. Open the page and use it. An Ulkaa account is not needed for anything on this tool.
Does it run in my browser?
Yes. Your measurements are processed by code running in your browser tab, on your own device.
Is my data uploaded?
No. Your measurements are never sent to Ulkaa or to anyone else. You can check this yourself by watching the Network tab in your browser developer tools while you use the tool.
What is an annulus?
The region between two concentric circles, shaped like a flat ring.
Is it the same as the difference of the radii squared?
No. It is π times the difference of the squares, not the square of the difference.
More Area Calculator pages
- Area CalculatorPick a shape, enter its dimensions and get the area with the formula, the working and a labelled diagram, in the unit you need.
- Square Area CalculatorEnter the side of a square to get its area and perimeter.
- Rectangle Area CalculatorEnter the length and width of a rectangle to get its area and perimeter.
- Triangle Area CalculatorEnter the base and the perpendicular height of a triangle.
- Circle Area CalculatorEnter the radius of a circle to get its area and circumference.
- Ellipse Area CalculatorEnter the two semi-axes of an ellipse.
- Trapezoid Area CalculatorEnter the two parallel sides and the height.
- Parallelogram Area CalculatorEnter the base and the perpendicular height.
- Rhombus Area CalculatorEnter the two diagonals of a rhombus.
- Sector Area CalculatorEnter the radius and the central angle of a sector.
- Regular Polygon Area CalculatorEnter the number of sides and the side length.
- Hexagon Area CalculatorEnter the side of a regular hexagon.
- Land Area CalculatorEnter the sides of a plot and read its area in katha, decimal, bigha, acres and square feet.