# How to use the PI function

**What is the PI function?**

The PI function returns the number pi (ΒΆ).

### Table of Contents

- What is the number pi?
- PI Function Syntax
- PI Function Arguments
- PI Function Example
- How to convert radians to fractions of pi
- How to calculate the area of a circle
- How to calculate the circumference of a circle
- How to calculate the volume of a sphere
- How to calculate the area of a sphere
- How to calculate the volume of a cone

**1. What is the number pi?**

Pi is a irrational number meaning it cannot be expressed as a ratio of two integers. In other words, it has an infinite number of decimal places with no repeating pattern.

It is calculated by the ratio of the circumference of a circle to its diameter.

Ο = circumference / diameter

or

circumference = diameter * Ο

or

circumference = 2 * Ο * radius

this means that the diameter = 2 x radius.

**What is the circumference of a circle?**

The circumference is the linear distance enclosing the circle. The math formula for calculating the circumference is **C = 2Ο r**, read section 6 below for a detailed example.

**What is the diameter of a circle?**

The diameter of a circle is the straight line distance that passes through the center of the circle connecting one point on the circumference to another, going all the way across the circle. The diameter is the radius * 2

The math formula for calculating the **diameter (d)** based on the **circumference of a circle (c)** isΒ **d = c / Ο**

The math formula for calculating the **diameter** ** (d)** based on the **area of a circle (a)** isΒ **d = β(4 a / Ο)**

**What is the radius of a circle?**

The radius of a circle is the distance from the center point to any point on the circle's edge or circumference. The radius is the diameter / 2

The math formula for calculating the **radius (r)** based on the **area of a circle (a)** isΒ **r = β(a / Ο)**

The math formula for calculating the **radius** **(r)** based on the **circumference of a circle (c)** isΒ **r = c / (2 Ο)**

**Why is the PI function useful?**

The trigonometric functions in Excel accept radians as the angular measurement. The basic trigonometry ratios like sine, cosine and tangent come from the ratios of sides in a right triangle. Sine, cosine and tangent ratios relate the lengths of sides to angles in a right triangle. If you know one side and angle, you can use these ratios to find the other sides. The ratios link geometry and angles together.

**What is the relationship between the number pi and radians?**

Radians measure angles by the length of the arc they make in a circle rather than degrees. The full circumference of any circle is 2Ο multiplied by the circle's radius (2Οr).

Since the circumference goes all the way around a circle, that means the full circle measures 2Ο radians. Half a circle would be Ο radians (half of 2Ο). A quarter circle is 2Ο/4 = Ο/2 radians. An eighth of a circle is 2Ο/8 = Ο/4 radians.

**What is a segment in a circle?**

A segment (also called chord) connects two points on a circle's edge by a straight line, and can be used to analyze geometric aspects of the circle like angles, area, and tangents.

**What is an arc in a circle?**

The arc in a circle is a segment of the circle's circumference. Arcs are an angle measured in degrees or radians.

**What is a sector?**

A sector of a circle is the section enclosed by two radii and an arc.

**What is radii?**

The plural form of the word "radius".

**What is the connection between a circle and trigonometry?**

The geometry of the circle underlies the theory, definitions, models, identities, and applications of trigonometry. The circle and trigonometry are deeply mathematically connected.

**What is the relationship between radians and degrees?**

The circumference of a circle is 360 degrees or 2Ο radians.

360 degrees = 2Ο radians

which is

degrees = radians x (180 / Ο)

## 2. PI Function Syntax

PI()

## 3. PI Function Arguments

PI function has no arguments.

## 4. PI Function example

Formula in cell B3:

The PI function returns 15 digits and is useful, for example, when graphing a SIN, COS or TAN curve. It is also useful for calculating circumferences, areas and volumes of circles, spheres, and cones etc.

## 5. How to convert radians to fractions of pi

The formula in cell D3 converts the radian decimal value to fractions of pi.

Formula in cell D3:

### Explaining the formula in cell D3

#### Step 1 - Divide radian by pi

The first operation is the division between the radian number and pi.

C3/PI()

becomes

6.28318530717959/PI()

The PI function returns the number pi (ΒΆ).

Function syntax: PI()

6.28318530717959/PI()

becomes

6.28318530717959/3.14159265358979

and returns 2

#### Step 2 - Calculate fractions

The TEXT function converts a value to text in a specific number format.

Function syntax: TEXT(value, format_text)

TEXT(C3/PI(),"?/?")

becomes

TEXT(2,"?/?")

and returns "2/1".

#### Step 3 - Display the PI character

The CHAR function converts aΒ number to the corresponding ANSI character determined by your computers character set.

Function syntax: CHAR(text)

The CHAR function inserts the pi symbol using ANSI code 182.

CHAR(182)

returns ΒΆ

#### Step 4 - Join values

Lastly, the ampersands concatenate the values.

TEXT(C3/PI(),"?/?")&"*"&CHAR(182)

becomes

"2/1"&"*"&ΒΆ

and returns "2/1*ΒΆ".

## 6. How to calculate the area of a circle

The PI function lets you calculate the area of a circle based on the diameter or radius. The math formula for calculating the area of a circle is **A = Ο rΒ².**

**A** is the area

**Ο** is pi

**r** is the radius

The formula in cell C6 calculates the area of a circle based on the specified radius in cell C4.

Formula in cell C6:

Area = Ο 5Β² = approx. 78.54

### Explaining the formula

#### Step 1 - Calculate the pi

PI() returns an approx. 3.14159265358979

#### Step 2 - Raise the radius to the power of 2

The caret character ^ lets you raise number to the power of n. It is the same as the POWER function but only one character making the formula smaller.

C4^2

becomes

5^2

equals 25

#### Step 3 - Multiply pi by the radius^2

PI()*C4^2

becomes

3.14159265358979 * 25

equals 78.5398163397448

## 7. How to calculate the circumference of a circle

The PI function lets you calculate the circumference of a circle based on the diameter or radius. The math formula for calculating the area of a circle is **C = 2Ο r.**

**C** is the circumference

**Ο** is pi

**r** is the radius

Formula in cell C6:

### Explaining the formula

#### Step 1 - Calculate the pi

PI() returns an approx. 3.14159265358979

#### Step 2 - Multiply the radius by 2

C4*2

becomes

5*2

equals 10

#### Step 3 - Multiply pi by the product

PI()*C4*2

becomes

3.14159265358979 * 10

equals 31.4159265358979

## 8. How to calculate the volume of a sphere

The PI function lets you calculate the volume of a sphere based on the diameter or radius. The math formula for calculating the volume of a sphere is **V = 4/3 Ο r ^{3}.**

**V** is the volume

**Ο** is pi

**r** is the radius

**What is a sphere?**

A sphere is a perfectly round 3-dimensional geometric shape. The distance from the center to any point on the surface is called the radius. All radii of a sphere are equal.

The rounded surface has no edges and curves smoothly. Spheres have rotational symmetry, they look the same when rotated in any direction.

Formula in cell C6:

### Explaining the formula

#### Step 1 - Raise the radius to the power of three

C4^3

becomes

5^3

and returns 125

#### Step 2 - Multiply constants

4/3*PI()*C4^3

becomes

4/3*PI()*125

and returns approx. 523.599

**How to calculate the radius based on the volume of a sphere?**

The math formula for calculating the radius (r) based on the volume of a sphere (V) is **r = ^{3}β(3V/(4Ο))**

## 9. How to calculate the area of a sphere

The PI function lets you calculate the area of a sphere based on the diameter or radius. The math formula for calculating the area of a sphere is **A = 4 Ο r ^{2}.**

**A** is the area

**Ο** is pi

**r** is the radius

Formula in cell C6:

### Explaining the formula

#### Step 1 - Raise the radius to the power of three

C4^2

becomes

5^2

and returns 25

#### Step 2 - Multiply constants

4*PI()*C4^2

becomes

4*PI()*25

and returns approx. 314.159

**How to calculate the radius based on the area of a sphere?**

The math formula for calculating the radius (r) based on the area of a sphere (A) is **r = β(A/(4Ο))**

## 10. How to calculate the volume of a cone

The PI function lets you calculate the volume of a cone based on the radius and the height. The math formula for calculating the volume of a cone is **V =Β 1/3 Ο r ^{2}Β h**

**V** is the volume

**Ο** is pi

**r** is the radius

**h** is the height

Formula in cell C6:

### Explaining the formula

#### Step 1 - Square the radius

The caret character ^ lets you raise number to the power of n. It is the same as the POWER function but only one character making the formula smaller.

C4^2

becomes

5^2

equals 25

#### Step 1 - Multiply constants

1/3*PI()*C6*C4^2

becomes

1/3*3.14159265358979*9*25

equals

235.619

**How to calculate the height of a cone based on the volume and radius?**

**h = 3V/(Ο r ^{2})**

**V** is the volume

**Ο** is pi

**r** is the radius

**h** is the height

**How to calculate the radius of a cone based on the volume and height?**

**r = β(3V/(Ο h))**

**V** is the volume

**Ο** is pi

**r** is the radius

**h** is the height

### Get Excel *.xlsx file

Convert radians to fractions of pi.xlsx

### 'PI' function examples

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### Functions in 'Math and trigonometry' category

The PI function function is one of 73 functions in the 'Math and trigonometry' category.

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Very good source of information on converting radians to the fractions of pi. Thanks to the writer for sharing this very important information.