{
  "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": "container-check-digit-calculator",
  "title": "Container Check Digit Calculator",
  "shortTitle": "Container Check Digit",
  "canonicalUrl": "https://cargomath.com/tools/container-check-digit-calculator/",
  "endpoints": {
    "html": "https://cargomath.com/tools/container-check-digit-calculator/",
    "json": "https://cargomath.com/tools/container-check-digit-calculator.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 and validate the ISO 6346 check digit for ocean freight container numbers using owner code, equipment category, and six-digit serial number.",
  "answer": "A container check digit is calculated from the first 10 ISO 6346 characters by converting letters to numeric values, multiplying each position by powers of two, and taking the weighted sum modulo 11.",
  "audience": "Freight forwarders, importers, and cross-border operators checking container IDs before booking, gate-in, bill of lading, EDI, or tracking updates.",
  "keywords": [
    "container check digit calculator",
    "ISO 6346 check digit",
    "container number validator",
    "shipping container check digit",
    "container ID check digit"
  ],
  "faq": [
    {
      "q": "What is a container check digit?",
      "a": "It is the final digit in an ISO 6346 container number, used to detect typing errors in the owner code, category letter, and six-digit serial number."
    },
    {
      "q": "Can this validate a full container number?",
      "a": "Yes. Paste an 11-character container number such as MSKU1234565 and the calculator compares the supplied final digit with the computed digit."
    },
    {
      "q": "What does the U category mean?",
      "a": "U is the standard ISO 6346 equipment category for freight containers. J is used for detachable equipment and Z for trailers or chassis."
    },
    {
      "q": "Why can the remainder 10 become check digit 0?",
      "a": "ISO 6346 uses modulo 11, but the printed check digit must be one decimal digit, so a remainder of 10 is represented as 0."
    },
    {
      "q": "Does a valid check digit prove the container exists?",
      "a": "No. It only proves the number passes the ISO 6346 arithmetic check; it does not confirm ownership, availability, location, or carrier release."
    },
    {
      "q": "Where should freight teams use this?",
      "a": "Use it before sending container numbers to carriers, terminals, customs brokers, customers, EDI systems, or shipment-tracking workflows."
    }
  ],
  "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-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 check digit."
      }
    ],
    "formula": "check_digit = (sum(character_value * 2^position_index) mod 11); use 0 when the remainder is 10",
    "limitations": [
      "Validates the ISO 6346 arithmetic only; it does not verify live container ownership or tracking events.",
      "Owner 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"
}