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Circle Calculator to Calculate Area, Circumference, Diameter, Radius

Calculator Preferences
Circle Calculator Sign
Circle Calculator

This calculator will solve for the three unknown circle measurements from one known measurement (area, circumference, diameter, or radius). Plus, the calculator displays the steps, formulas, and sequence used to calculate each unknown measurement in the results. The Learn tab includes a circle diagram depicting each measurement, accompanied by a brief definition of each and the method of solving for them.

Learn More

Selected Data Record:

A Data Record is a set of calculator entries that are stored in your web browser's Local Storage. If a Data Record is currently selected in the "Data" tab, this line will list the name you gave to that data record. If no data record is selected, or you have no entries stored for this calculator, the line will display "None".

DataData recordData recordSelected data record: None
Convert Ft/In to DecimalConvert Feet/Inches to DecimalConvert Feet/Inches to DecimalConvert Feet/Inches to Decimal

Enter the feet, inches, and fraction of an inch, and then click the Convert to Decimal button. You can then copy the appropriate decimal and paste into the circle calculator.

Feet:
Inches:
-/
Feet:
Inches:

Convert Feet/Inches to Decimal:

If you need to convert a tape measurement into a decimal number, tap the button in this row to expand the converter.

Dec places:Decimal places:Number of decimal places:Number of decimal places to round result to:

Number of decimal places:

Select how many decimal places you would like the result rounded to. Note that you can change the number of places before or after calculating the circle measurement. Also note that the circle calculator will always display the raw results (out to 14 places) in the steps that will appear beneath the calculator.

Area (A):

Select the known value and just start typing.

Circle Area Calculator
A =

Mini Circle Area Calculator:

Select the known circle measurement from the drop-down menu and then enter the selected measurement in decimal format. The circle's area (A) will be calculated as you type. Click the Clear button to clear both fields.

Area (A):

If you know the area of the circle and would like to calculate the circumference, diameter, and radius, enter the area on this line. Enter only digits 0-9 and a decimal point (if applicable). Non-numeric characters will not compute.

Or, tap the plus (+) to expand the mini calculator if you need to find the area.

Note that the area of a circle is expressed as the square of the particular unit of measurement being used (square mm, square inches, etc.).

 
Circumference (C):
Circumference Calculator
C =

Mini Circumference Calculator:

Select the known circle measurement from the drop-down menu and then enter the selected measurement in decimal format. The circle's circumference (C) will be calculated as you type. Click the Clear button to clear both fields.

Circumference (C):

If you know the circumference of the circle and would like to calculate the area, diameter, and radius, enter the circumference on this line. Enter only digits 0-9 and a decimal point (if applicable). Non-numeric characters will not compute.

Or, tap the plus (+) to expand the mini calculator if you need to find the circumference.

 
Diameter (D):

Select the known value and just start typing.

Diameter Calculator
D =

Mini Diameter Calculator:

Select the known circle measurement from the drop-down menu and then enter the selected measurement in decimal format. The circle's diameter (D) will be calculated as you type. Click the Clear button to clear both fields.

Diameter (D):

If you know the diameter of the circle and would like to calculate the area, circumference, and radius, enter the diameter in the field on this line. Enter only digits 0-9 and a decimal point (if applicable). Non-numeric characters will not compute.

Or, tap the plus (+) to expand the mini calculator if you need to find the diameter.

 
Radius (r):

Select the known value and just start typing.

Radius Calculator
d =

Mini Radius Calculator:

Select the known circle measurement from the drop-down menu and then enter the selected measurement in decimal format. The circle's radius (r) will be calculated as you type. Click the Clear button to clear both fields.

Radius (r):

If you know the radius of the circle and would like to calculate the area, circumference, and diameter, enter the radius in the field on this line. Enter only digits 0-9 and a decimal point (if applicable). Non-numeric characters will not compute.

Or, tap the plus (+) to expand the mini calculator if you need to find the radius.

 

If you would like to save the current entries to the secure database, tap or click on the Data tab, select "New Data Record", give the data record a name, then tap or click the Save button. To save changes to previously saved entries, simply tap the Save button. Please select and "Clear" any data records you no longer need.

Convert Decimal to Ft/InConvert Decimal to Feet/InchesConvert Decimal to Feet/InchesConvert Decimal to Feet/Inches

Enter the decimal number, tap Feet or Inches, select the maximum denominator, and then click the Convert to Feet/Inches button. The converter will round the fraction portion to the selected denominator and then reduce it to simplest form.

Decimal:
Type:
Max Denom:Max Denom:Max Denominator:Maximum Denominator:
Feet:
Inches:
-/

Convert Feet/Inches to Decimal:

If you need to convert a decimal to a tape measurement, copy a decimal from the above results and tap the button to expand the converter.

Decimal number:

Enter the decimal number you would like to convert into a tape measurement.

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Tip

Help and Tools

Help and Tools:

This section, which you can Unstick or Hide in the Calculator Preferences (just above the top of the calculator), contains the following tabs (content too long to fit within bordered frame can be scrolled up and down):

About: Click this tab for an introduction to the calculator.

Instructions: Click this tab for step-by-step instructions for using the calculator.

Terms: Click this tab for a list of the descriptions that are located within each popup help button (info icons).

PCalc: Click this tab for a handy "pocket" calculator you can use when you need to calculate an entry needed for the calculator.

Data: Click this tab to save a set of entries or a note in between visits. Entries and notes will be stored to your web browser's local storage (if supported by your browser of choice), meaning they can only be recalled with the same device and web browser you were using when you saved them. If you'd like to save entries and notes between devices you can do so by subscribing to the Ad-Free Member Version.

 

Favorites

Add or remove this page to/from my favorites.

Adjust Calculator Width:

Move the slider to left and right to adjust the calculator width. Note that the Help and Tools panel will be hidden when the calculator is too wide to fit both on the screen. Moving the slider to the left will bring the instructions and tools panel back into view.

Also note that some calculators will reformat to accommodate the screen size as you make the calculator wider or narrower. If the calculator is narrow, columns of entry rows will be converted to a vertical entry form, whereas a wider calculator will display columns of entry rows, and the entry fields will be smaller in size ... since they will not need to be "thumb friendly".

Show/Hide Popup Keypads:

Select Show or Hide to show or hide the popup keypad icons located next to numeric entry fields. These are generally only needed for mobile devices that don't have decimal points in their numeric keypads. So if you are on a desktop, you may find the calculator to be more user-friendly and less cluttered without them.

Stick/Unstick Tools:

Select Stick or Unstick to stick or unstick the help and tools panel. Selecting "Stick" will keep the panel in view while scrolling the calculator vertically. If you find that annoying, select "Unstick" to keep the panel in a stationary position.

If the tools panel becomes "Unstuck" on its own, try clicking "Unstick" and then "Stick" to re-stick the panel.