Container Numbers Explained: Your Simple Guide

If you've ever looked at a shipping container, you've seen a number painted on the side that looks like random letters and numbers. It's not random, it's a standardized system used worldwide.

Let's break down what those numbers mean using MSDU7123898 as our example.

The 4 Parts of a Container Number

MSDU7123898 breaks down like this:

• MSD (positions 1-3) = Owner code
• U (position 4) = Equipment type
• 712389 (positions 5-10) = Serial number
• 8 (position 11) = Check digit

Owner Code (First 3 Letters): MSD

This tells you who owns the container.

• MSD = Mediterranean Shipping Company
• MAE = Maersk
• COS = COSCO
• ONE = Ocean Network Express

These codes are registered internationally to ensure no two companies use the same code.

Equipment Type (4th Letter): U

This tells you what type of equipment it is.

• U = Standard freight container (95% of what you'll see)
• J = Detachable equipment
• Z = Trailers or chassis

Serial Number (Next 6 Digits): 712389

This is the unique ID number the owner assigns. No two containers owned by the same company will have the same serial number—think of it like a license plate.

Check Digit (Last Digit): 8

This is the error-catching digit, mathematically calculated from all previous characters. When you type MSDU7123898 into a system, it automatically verifies that final "8" is correct. Type MSDU7123897 instead, and the system flags the error.

Why This Matters

Tracking & Documentation

The number MSDU7123898 appears on every document: bill of lading, customs forms, delivery orders, VGM declarations, and terminal receipts. One wrong digit means your cargo can't be found.

Error Prevention

The check digit catches about 90% of common errors:

• Wrong digits: MSDU7123888
• Swapped digits: MSDU7123989
• OCR scanning errors

How The Check Digit Works

Here's what happens when validating MSDU7123898:

Step 1: Convert Letters to Numbers

A=10, B=12, C=13, D=14, E=15, F=16, G=17, H=18, I=19, J=20, K=21, L=23, M=24, N=25, O=26, P=27, Q=28, R=29, S=30, T=31, U=32, V=34, W=35, X=36, Y=37, Z=38

For MSDU: M=24, S=30, D=14, U=32

Step 2: Multiply by Position Weights

Each position has a weight: 1, 2, 4, 8, 16, 32, 64, 128, 256, 512

Step 3: Calculate

• M (24) × 1 = 24
• S (30) × 2 = 60
• D (14) × 4 = 56
• U (32) × 8 = 256
• 7 × 16 = 112
• 1 × 32 = 32
• 2 × 64 = 128
• 3 × 128 = 384
• 8 × 256 = 2048
• 9 × 512 = 4608

Total: 7,708

Step 4: Divide by 11

7,708 ÷ 11 = 700 remainder 8

The remainder (8) matches the check digit (8) = VALID

Special rule: If remainder = 10, check digit = 0

Spotting Invalid Numbers

Wrong length:

• "MSDU712389" (10 characters)
• "MSDU71238988" (12 characters)

Wrong format:

• "MSD7123898" (only 3 letters)
• "7123MSD898U" (wrong order)

Failed validation:

• "MSDU7123897" (check digit should be 8)

Real-World Impact

Scenario: You type MSDU7123897 instead of MSDU7123898 on your customs form.

Result:

1. System flags invalid check digit
2. Customs rejects submission
3. Hours or days of delay
4. OR worse—if you enter a different valid number, you might try to collect someone else's cargo