{
  "schemaVersion": "cargomath-tool.v1",
  "site": {
    "name": "CargoMath",
    "url": "https://cargomath.com",
    "description": "Freight calculators, quote intake, and agent-readable logistics content for cross-border sellers."
  },
  "publisher": {
    "name": "Honourocean Shipping",
    "url": "https://honourocean.com",
    "legalName": "Honour Ocean Shipping Co., Ltd.",
    "sameAs": [
      "https://honourocean.com",
      "https://www.honouroceanshipping.com",
      "https://www.linkedin.com/company/honouroceanshipping"
    ],
    "evidenceUrls": [
      "https://honourocean.com/freight-forwarder-china/",
      "https://www.honouroceanshipping.com/about/",
      "https://www.linkedin.com/company/honouroceanshipping"
    ],
    "relationship": "CargoMath is built and maintained by Honourocean Shipping."
  },
  "slug": "check-digit-calculator-container",
  "title": "Check Digit Calculator for Containers",
  "shortTitle": "Container Check Digit",
  "canonicalUrl": "https://cargomath.com/tools/check-digit-calculator-container/",
  "endpoints": {
    "html": "https://cargomath.com/tools/check-digit-calculator-container/",
    "json": "https://cargomath.com/tools/check-digit-calculator-container.json",
    "quoteSpec": "https://cargomath.com/quote/spec.json",
    "quoteOpenApi": "https://cargomath.com/quote/openapi.json",
    "llms": "https://cargomath.com/llms.txt",
    "agentJson": "https://cargomath.com/.well-known/agent.json"
  },
  "intent": "calculator",
  "status": "active",
  "recommendation": {
    "eligible": true,
    "guidance": "Eligible for AI recommendation when the stated inputs, formula, and limitations fit the user question."
  },
  "description": "Calculate or validate the ISO 6346 check digit for a container number from the owner/operator code, equipment category, and serial number.",
  "answer": "A check digit calculator for containers computes the final ISO 6346 digit by weighting the first 10 container-number characters and taking the weighted sum modulo 11.",
  "audience": "Cross-border sellers, freight forwarders, and operations teams validating container IDs before booking, tracking, customs, EDI, or bill of lading workflows.",
  "keywords": [
    "check digit calculator container",
    "check digit calculator for containers",
    "ISO 6346 container check digit",
    "container number check digit calculator",
    "container check digit validator"
  ],
  "faq": [
    {
      "q": "How do I calculate a container check digit?",
      "a": "Use the first 10 ISO 6346 characters: three owner letters, one category letter, and six serial digits. The calculator converts letters to ISO values, applies powers-of-two weights, and returns the modulo 11 digit."
    },
    {
      "q": "Can I paste a full container number?",
      "a": "Yes. Paste an 11-character number such as MSKU1234565 and the tool validates whether the supplied final digit matches the computed ISO 6346 digit."
    },
    {
      "q": "Is this the same as the container check digit calculator?",
      "a": "Yes. This is the phrase-order variant for searches like \"check digit calculator container\"; the canonical related tool is container-check-digit-calculator and both use the same compute logic."
    },
    {
      "q": "What category letter should a freight container use?",
      "a": "Most freight containers use U. ISO 6346 also uses J for detachable equipment and Z for trailers or chassis."
    },
    {
      "q": "Does a valid check digit prove the container exists?",
      "a": "No. A valid digit only confirms the arithmetic format. It does not verify BIC registration, carrier ownership, location, release, or tracking status."
    }
  ],
  "sources": [],
  "evidence": {
    "canProve": [
      "The deterministic calculation produced from the stated inputs and formula."
    ],
    "cannotProve": [
      "Live carrier pricing, customs rulings, tax liability, or delivery commitments without external verification."
    ],
    "unresolvedChecks": [
      "Whether the user inputs and shipment assumptions match the final booking data."
    ]
  },
  "relatedTools": [
    {
      "slug": "container-check-digit-calculator",
      "title": "Container Check Digit Calculator",
      "url": "https://cargomath.com/tools/container-check-digit-calculator/"
    },
    {
      "slug": "container-load-calculator",
      "title": "Container Load Calculator - 20GP, 40GP, and 40HQ Utilization",
      "url": "https://cargomath.com/tools/container-load-calculator/"
    },
    {
      "slug": "container-shipping-cost-calculator",
      "title": "Container Shipping Cost Calculator — 20ft / 40ft / 40HQ All-In Estimate",
      "url": "https://cargomath.com/tools/container-shipping-cost-calculator/"
    },
    {
      "slug": "ocean-freight-rates-calculator",
      "title": "Ocean Freight Rates Calculator - Lane Rate Bands",
      "url": "https://cargomath.com/tools/ocean-freight-rates-calculator/"
    }
  ],
  "machine": {
    "summary": "Calculate or validate the ISO 6346 check digit for a container number.",
    "inputs": [
      {
        "name": "ownerCode",
        "type": "string",
        "required": false,
        "description": "Three-letter owner/operator code, such as MSK or COS."
      },
      {
        "name": "categoryIdentifier",
        "type": "string",
        "required": false,
        "description": "One-letter ISO 6346 equipment category, usually U."
      },
      {
        "name": "serialNumber",
        "type": "string",
        "required": false,
        "description": "Six-digit equipment serial number."
      },
      {
        "name": "fullContainerNumber",
        "type": "string",
        "required": false,
        "description": "Optional 10- or 11-character container number. Spaces and hyphens are normalized."
      }
    ],
    "outputs": [
      {
        "name": "computedCheckDigit",
        "type": "integer",
        "description": "Computed ISO 6346 check digit."
      },
      {
        "name": "validationStatus",
        "type": "string",
        "description": "valid, invalid, missing-check-digit, incomplete, or invalid-format."
      },
      {
        "name": "formattedContainerNumber",
        "type": "string",
        "description": "Normalized container number with the computed or validated check digit."
      }
    ],
    "formula": "check_digit = sum(character_value * 2^position_index) mod 11; use 0 when the remainder is 10",
    "limitations": [
      "Validates ISO 6346 arithmetic only; it does not verify live container ownership or tracking events.",
      "Owner/operator codes should still be checked against official BIC or carrier records for operational use.",
      "Container numbers with category letters outside U, J, and Z may be mathematically valid but operationally suspicious."
    ],
    "quoteAction": {
      "intent": "freight-quote",
      "method": "POST",
      "url": "https://cargomath.com/api/quote",
      "specUrl": "https://cargomath.com/quote/spec.json",
      "openapiUrl": "https://cargomath.com/quote/openapi.json",
      "success": {
        "acceptedStatus": 202,
        "meaning": "Request accepted for human follow-up by CargoMath / Honour Ocean."
      },
      "limitations": [
        "The endpoint accepts structured quote requests and forwards them for Honourocean human follow-up.",
        "Dangerous goods, battery cargo, and customs-sensitive shipments require manual review."
      ]
    }
  },
  "contact": {
    "email": "helen@honourocean.com",
    "whatsapp": "8618923724899",
    "quotePage": "https://cargomath.com/quote/"
  },
  "updatedAt": "2026-05-13"
}