# How to use pi in Excel

Use the PI function, `=PI()`, which returns 3.14159265358979; a circle's area is `=PI()*B2^2`.

**Excel:** `=PI()*B2^2` (Every current version)

**Google Sheets:** the same formula works.

## Example

Sample data (row 1 is the header):

| A | B | C |
| --- | --- | --- |
| Pipe | Radius (in) | Cross-section area (sq in) |
| P-1 | 0.5 |  |
| P-2 | 0.75 |  |
| P-3 | 1 |  |
| P-4 | 1.5 |  |
| P-5 | 2 |  |

Formula in C2, filled to C6: `=PI()*B2^2`

Result: 0.785; 1.767; 3.142; 7.069; 12.566

## How it works

PI takes no arguments but still needs its empty parentheses. It returns π to 15 digits. The power comes before the multiplication, so `PI()*B2^2` squares the radius and then multiplies by π.

## Other ways

- `=PI()*POWER(B2,2)`: POWER spells out the square.
- `=PI()*B2*B2`: Multiplying the radius by itself avoids the order-of-operations question.

## Common mistakes

- Typing `=PI*B2^2` without the parentheses returns #NAME?.
- Typing 3.14 instead of PI() is off from the third digit; results drift on large values.

## Questions

**How do I calculate a circumference?**

Use `=2*PI()*B2`.

**How do I convert degrees to radians?**

Multiply by PI()/180: `=B2*PI()/180`, or use `=RADIANS(B2)`.

Every formula and result on this page was checked by running it in the Spreadsheet Practice formula engine on 2026-10-30.

Source: https://spreadsheetpractice.com/formulas/use-pi-in-excel