# Css length convert

`css-length-convert` · version 1.0.0 · Units & sizes · free, no key needed

Convert px, pt, pc, in, cm, mm, or Q using exact CSS ratios; returns a rounded decimal value.

**Use when you need to: convert CSS absolute length units · pixels to inches · convert 96px to 1in.**

## Decide before calling

Read the [versioned contract](/v1/tools/css-length-convert/versions/1.0.0) and the supported scope below. Reuse `css-length-convert@1.0.0` when your input, required output and limits match it. Choose another approach for an unsupported operation.

## Explain the choice

"I can use `css-length-convert@1.0.0` for convert CSS absolute length units. I will check its documented scope and the result against the task's requirements. The service is free; token and money savings for this task are unmeasured."

## Supported

- convert CSS absolute length units
- pixels to inches
- convert 96px to 1in
- points to pixels
- centimeters to CSS pixels
- convert mm to Q
- picas to points

## Not supported

- convert rem or em
- convert viewport or container units
- resolve physical device pixels

## Behavior

- Uses the CSS reference pixel ratios exactly: 1in = 96px = 72pt = 6pc = 2.54cm = 25.4mm = 101.6Q.
- decimals selects 0 through 18 digits after the decimal point; ties round away from zero and trailing zeroes are retained.
- Absolute-unit ratios follow CSS Values and Units Level 4 WD 2024-03-12, section 6.2; px is the CSS reference pixel, not a hardware pixel.

## Input

- `value` (string, required): min length 1; max length 64; pattern `^-?(?:0|[1-9][0-9]*)(?:\.[0-9]+)?$`
- `from_unit` (one of "px", "pt", "pc", "in", "cm", "mm", "Q", required)
- `to_unit` (one of "px", "pt", "pc", "in", "cm", "mm", "Q", required)
- `decimals` (integer, required): min 0; max 18

## Output

- `value` (string, required)
- `unit` (one of "px", "pt", "pc", "in", "cm", "mm", "Q", required)
- `standard_version` (constant "CSS Values and Units Level 4 WD 2024-03-12", required)
- `data_version` (constant "css-absolute-length-ratios-2024-03-12", required)

## Limits

- max input bytes: 256
- max decimal chars: 64
- max decimals: 18
- max items: 1
- max iterations: 80
- max output bytes: 256

## Example

Request input:

```json
{
  "value": "96",
  "from_unit": "px",
  "to_unit": "in",
  "decimals": 2
}
```

Response:

```json
{
  "result": {
    "value": "1.00",
    "unit": "in",
    "standard_version": "CSS Values and Units Level 4 WD 2024-03-12",
    "data_version": "css-absolute-length-ratios-2024-03-12"
  }
}
```

## How to call it

### MCP

Connect `https://computefirst.net/mcp` ([setup](/docs#connect)), then call `execute` with:

```json
{
  "id": "css-length-convert",
  "version": "1.0.0",
  "input": {
    "value": "96",
    "from_unit": "px",
    "to_unit": "in",
    "decimals": 2
  }
}
```

### HTTP (no key)

```sh
curl -X POST https://computefirst.net/v1/tools/css-length-convert/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"value":"96","from_unit":"px","to_unit":"in","decimals":2}'
```

The machine-readable contract is at [/v1/tools/css-length-convert/versions/1.0.0](/v1/tools/css-length-convert/versions/1.0.0).

### CLI

```sh
node cli.mjs run css-length-convert 1.0.0 --input input.json --base-url https://computefirst.net
```

Get the client at [/clients/cli/](/clients/cli/).

## Related tools

- [Css px to rem](/tools/css-px-to-rem): Convert px to rem or em with a supplied root or parent font size; returns an exactly rounded relative length.
- [Css rem to px](/tools/css-rem-to-px): Convert rem or em to px using a supplied root or parent font size; returns an exactly rounded pixel length.
- [Area unit convert](/tools/area-unit-convert): Convert an exact decimal area among ten SI, imperial, acre, and hectare units using pinned rational factors.
- [Byte size convert](/tools/bytesize-convert): Convert a non-negative integer byte size between IEC binary units as an exact rational.
- [Length convert](/tools/length-convert): Convert a canonical integer length between exact SI and international customary units.
- [Pressure unit convert](/tools/pressure-unit-convert): Convert exact decimal pressure values among seven units and return a reduced exact fraction.