Endpoint: Cost Estimate

Method + path

GET /convert/estimate/{from}/{to}

Auth

Requires X-Fast-Api-Key header.

Path params

• from: source format (e.g. heic, pdf, wav)
• to: target format (e.g. jpg, png, mp3)

Query params

All optional. Provide the relevant parameter for the converter's costing strategy to receive an estimatedCredits value.

If both fileSizeBytes and fileSizeMb are provided, fileSizeBytes takes precedence.

Important: If the required input for the strategy is omitted, estimatedCredits returns the base cost — this is the minimum cost, not a calculated estimate. For example, a 200-page PDF-to-JPG conversion costs 20 credits, but omitting pageCount returns estimatedCredits: 1. Always provide the relevant input parameter for an accurate estimate.

The costing formula and limits are always returned so clients can calculate or display the rate.

Response

200 OK with CostEstimateResponse.

Example response (PerMegabyte strategy — no inputs)

When no size input is provided, estimatedCredits returns the base cost (minimum).

{
  "job": "image.heic-to-jpg",
  "category": "images",
  "estimatedCredits": 1,
  "costing": {
    "strategy": "PerMegabyte",
    "baseCost": 1,
    "increment": 5,
    "incrementUnit": "mb",
    "displaySuffix": "per 5 MB",
    "costVariants": null
  },
  "inputs": {
    "fileSizeBytes": null,
    "fileSizeMb": null,
    "pageCount": null,
    "durationMinutes": null
  },
  "limits": {
    "maxFileSizeBytes": 1073741824,
    "maxPages": null,
    "maxDurationMinutes": null
  }
}

Example response (PerPage with input)

{
  "job": "document.pdf-to-jpg",
  "category": "documents",
  "estimatedCredits": 10,
  "costing": {
    "strategy": "PerPage",
    "baseCost": 1,
    "increment": 5,
    "incrementUnit": "pages",
    "displaySuffix": "per 5 pages",
    "costVariants": null
  },
  "inputs": {
    "fileSizeBytes": null,
    "fileSizeMb": null,
    "pageCount": 50,
    "durationMinutes": null
  },
  "limits": {
    "maxFileSizeBytes": 1073741824,
    "maxPages": 2000,
    "maxDurationMinutes": null
  }
}

Example response (PerPage without input — minimum only)

Caution: This response shows estimatedCredits: 1 because pageCount was omitted — this is not the cost of converting a multi-page PDF. Pass pageCount for an accurate estimate.

{
  "job": "document.pdf-to-jpg",
  "category": "documents",
  "estimatedCredits": 1,
  "costing": {
    "strategy": "PerPage",
    "baseCost": 1,
    "increment": 5,
    "incrementUnit": "pages",
    "displaySuffix": "per 5 pages",
    "costVariants": null
  },
  "inputs": {
    "fileSizeBytes": null,
    "fileSizeMb": null,
    "pageCount": null,
    "durationMinutes": null
  },
  "limits": {
    "maxFileSizeBytes": 1073741824,
    "maxPages": 2000,
    "maxDurationMinutes": null
  }
}

Example response (PerMinute with cost variants)

Converters with cost variants include a costVariants object in the costing response. Use the variant query parameter to select a non-default cost tier.

{
  "job": "audio.audio-to-txt",
  "category": "audio",
  "estimatedCredits": 50,
  "costing": {
    "strategy": "PerMinute",
    "baseCost": 2,
    "increment": 1,
    "incrementUnit": "minutes",
    "displaySuffix": "per minute",
    "costVariants": {
      "optionKey": "transcription.mode",
      "label": "Transcription mode",
      "default": "fast",
      "variants": {
        "fast": { "cost": 2, "label": "Fast" },
        "quality": { "cost": 5, "label": "Quality" },
        "meeting-intelligence": { "cost": 8, "label": "Meeting Intelligence" }
      }
    }
  },
  "inputs": {
    "fileSizeBytes": null,
    "fileSizeMb": null,
    "pageCount": null,
    "durationMinutes": 10.0
  },
  "limits": {
    "maxFileSizeBytes": 1073741824,
    "maxPages": null,
    "maxDurationMinutes": 300
  }
}

Examples

# PerMegabyte (no inputs — returns base cost)
curl -sS "https://api.tools.fast/convert/estimate/heic/jpg"

# PerMegabyte with file size (bytes)
curl -sS "https://api.tools.fast/convert/estimate/heic/jpg?fileSizeBytes=52428800"

# PerMegabyte with file size (MB convenience alias)
curl -sS "https://api.tools.fast/convert/estimate/heic/jpg?fileSizeMb=50"

# PerPage with page count
curl -sS "https://api.tools.fast/convert/estimate/pdf/jpg?pageCount=50"

# PerMinute with duration
curl -sS "https://api.tools.fast/convert/estimate/wav/mp3?durationMinutes=12.5"

# PerMinute with cost variant (quality mode = 5 credits/min)
curl -sS "https://api.tools.fast/convert/estimate/mp3/txt?durationMinutes=10&variant=quality"

# Unsupported pair (returns 400)
curl -sS "https://api.tools.fast/convert/estimate/heic/mp3"

# PerMegabyte (no inputs — returns base cost)
Invoke-RestMethod "https://api.tools.fast/convert/estimate/heic/jpg"

# PerMegabyte with file size (bytes)
Invoke-RestMethod "https://api.tools.fast/convert/estimate/heic/jpg?fileSizeBytes=52428800"

# PerMegabyte with file size (MB convenience alias)
Invoke-RestMethod "https://api.tools.fast/convert/estimate/heic/jpg?fileSizeMb=50"

# PerPage with page count
Invoke-RestMethod "https://api.tools.fast/convert/estimate/pdf/jpg?pageCount=50"

# PerMinute with duration
Invoke-RestMethod "https://api.tools.fast/convert/estimate/wav/mp3?durationMinutes=12.5"

# PerMinute with cost variant (quality mode = 5 credits/min)
Invoke-RestMethod "https://api.tools.fast/convert/estimate/mp3/txt?durationMinutes=10&variant=quality"

# Unsupported pair (returns 400)
Invoke-RestMethod "https://api.tools.fast/convert/estimate/heic/mp3"

Error responses

400 Bad Request if the format pair is not supported:

{
  "error": "estimate.unsupported_format_pair",
  "detail": "Conversion from 'heic' to 'mp3' is not supported.",
  "sourceFormat": "heic",
  "targetFormat": "mp3",
  "supportedTargets": ["avif", "jpg", "png", "webp"]
}

400 Bad Request if an invalid cost variant is specified:

{
  "error": "estimate.invalid_variant",
  "detail": "Cost variant 'bogus' not found for option 'transcription.mode'. Valid: fast, quality, meeting-intelligence"
}