Pi Calculator
Enter any one of radius, circumference, or area to automatically calculate the rest
Input
Results
What is a Pi Calculator?
A Pi Calculator is a convenient tool that automatically computes the remaining values of a circle when you input just one known value among radius, circumference, or area. There’s no need to memorize complex formulas or perform manual calculations—simply enter the value you know, and instantly get all the results you need.
Key Features
Reverse Calculation Support
Even if you don’t know the radius, you can calculate it from the circumference or area. For instance, if the circumference is 31.42cm, just input this value to automatically determine the radius of 5cm and area of 78.54cm².
High-Precision Pi Value
The calculator uses a precise pi value of 3.14159265359, providing far more accurate results than using the simplified 3.14. With results displayed to six decimal places, it’s suitable even for applications requiring high precision.
Automatic Input Management
When you enter a value in one field, the other fields automatically clear, preventing errors from multiple simultaneous inputs. This ensures you always get accurate calculation results.
Pi Formulas
Circumference Formula (C = 2πr)
The circumference of a circle equals the radius multiplied by 2π. For example, a circle with a radius of 10cm has a circumference of 2 × 3.14159 × 10 = 62.83cm. This formula helps determine the perimeter length of a circle.
Area Formula (A = πr²)
The area of a circle equals pi multiplied by the square of the radius. A circle with a radius of 10cm has an area of 3.14159 × 10² = 314.16cm². This formula calculates the space occupied by a circle on a plane.
Practical Applications
Architecture and Interior Design
Calculate material requirements and dimensions when designing circular tables, lighting fixtures, or windows. For instance, determine the area of a 1.2m diameter circular table to select the right tablecloth size.
Manufacturing and Engineering
Precise dimension calculations are essential when fabricating pipes, circular components, or gears. Knowing the circumference helps calculate material length requirements, while the area determines cross-sectional measurements.
Landscaping and Agriculture
Determine material quantities needed for circular garden beds, fountains, or ponds. With just the radius, you can instantly calculate both perimeter length and area, making material purchasing straightforward.
Education and Learning
Quickly verify calculation results when solving math assignments or problems. Students can enhance their learning by understanding formulas first, then using the calculator to validate their answers.
How to Use
- Enter the known value (radius, circumference, or area) in the corresponding input field.
- Click the Calculate button or press Enter.
- View all calculated values in the results section.
- If needed, click the copy button next to any result to copy it to your clipboard.
Calculation Examples
When Radius is Known
To find the circumference and area of a circle with a radius of 7cm, enter 7 in the radius field. The results show a circumference of 43.98cm and an area of 153.94cm².
When Circumference is Known
To find the radius and area of a circle with a circumference of 50cm, enter 50 in the circumference field. The results show a radius of 7.96cm and an area of 199.04cm².
When Area is Known
To find the radius and circumference of a circle with an area of 100cm², enter 100 in the area field. The results show a radius of 5.64cm and a circumference of 35.45cm.
Important Notes
Enter only one value at a time for radius, circumference, or area. Entering multiple values simultaneously will trigger an error message. Additionally, only positive numbers greater than zero are accepted—entering negative numbers or zero will display an input error message.
Frequently Asked Questions
Why isn’t it exactly 3.14?
The value 3.14 is an approximation of pi, while the actual value is an irrational number that continues infinitely: 3.14159265359… This calculator uses a more precise value to deliver more accurate results.
How do I choose units?
The calculator works with numbers regardless of units. Whatever unit you use for input applies to the results. For example, if you enter the radius in centimeters, interpret the circumference in centimeters and the area in square centimeters.
How many decimal places are accurate?
Results are displayed to six decimal places and calculated using JavaScript’s floating-point precision internally. This provides sufficient accuracy for general purposes.