Text fit in a box API

Estimates characters per line, lines, and total character/word capacity for a box from font size, glyph width and line-height. Answers 'How much text fits in a 400x300px box at 16px?', 'Roughly how many words can this box hold?'.

Price$0.04per request

MethodPOST

Route/v1/design/text-fit-box

StatusLive

MIME typeapplication/json

Rate limit120/minute

Cache0s public

designtypographytext-fitcapacityboxcharacters-per-linelayoutestimate

API URLhttps://x402.hexl.dev/v1/design/text-fit-box

Integration docs

Example request

{
  "boxWidthPx": 400,
  "boxHeightPx": 300,
  "fontSizePx": 16
}

Example response

{
  "boxWidthPx": 400,
  "boxHeightPx": 300,
  "fontSizePx": 16,
  "charWidthPx": 8,
  "lineHeightPx": 22.4,
  "charactersPerLine": 50,
  "lines": 13,
  "capacityCharacters": 650,
  "capacityWords": 108,
  "interpretation": "≈50 chars/line × 13 lines ≈ 650 characters (~108 words)."
}

Input schema

{
  "type": "object",
  "required": [
    "boxWidthPx",
    "boxHeightPx",
    "fontSizePx"
  ],
  "properties": {
    "boxWidthPx": {
      "type": "number",
      "description": "Box width in px",
      "examples": [
        400
      ]
    },
    "boxHeightPx": {
      "type": "number",
      "description": "Box height in px",
      "examples": [
        300
      ]
    },
    "fontSizePx": {
      "type": "number",
      "description": "Font size in px",
      "examples": [
        16
      ]
    },
    "avgCharWidthEm": {
      "type": "number",
      "description": "Average glyph width in em (default 0.5)",
      "examples": [
        0.5
      ]
    },
    "lineHeight": {
      "type": "number",
      "description": "Line-height multiplier (default 1.4)",
      "examples": [
        1.4
      ]
    },
    "avgWordLength": {
      "type": "number",
      "description": "Average characters per word (default 5)",
      "examples": [
        5
      ]
    }
  }
}

Output schema

{
  "type": "object",
  "additionalProperties": true
}