# \eta

The η symbol (Greek small letter eta, U+03B7), written as \eta in LaTeX math mode.

https://texform.dev/latex/symbols/eta

## Metadata

| Field | Value |
| --- | --- |
| Topic | [Greek letters](https://texform.dev/latex/topics/greek) |
| Packages | base |
| Allowed mode | math |
| Glyph | η |
| Unicode | U+03B7 GREEK SMALL LETTER ETA |
| Delimiter | No |

## Syntax

```latex
\eta
```

Takes no arguments.

## Common tasks

### How to write a Greek eta

```latex
\eta
```

[Open in Playground](https://play.texform.dev/?input=%5Ceta)

### How to write an efficiency

```latex
\eta = \frac{P_{\mathrm{out}}}{P_{\mathrm{in}}}
```

[Open in Playground](https://play.texform.dev/?input=%5Ceta+%3D+%5Cfrac%7BP_%7B%5Cmathrm%7Bout%7D%7D%7D%7BP_%7B%5Cmathrm%7Bin%7D%7D%7D)

### How to write a Minkowski metric signature

```latex
\eta_{\mu\nu}
```

[Open in Playground](https://play.texform.dev/?input=%5Ceta_%7B%5Cmu%5Cnu%7D)

## Usage frequency

4.17% of formulas in the measured corpus contain this entry, rank 26 of 474 entries with frequency data.

## In TeXForm

TeXForm parses this entry as a character leaf mapped to U+03B7 (GREEK SMALL LETTER ETA).