system design: estimating storage

Some rules of thumb for data sizing:

• int - 4 bytes
• bigint - 8 byts
• float - 4 bytes
• date - 3 bytes
• datetime - 5 bytes
• single character - 2 bytes (depends on encoding)
• an email - 2 KB
• image (average) - 200 KB
• audio (per minute) - 1 MB
• image (good) - 2 MB
• video (per minute) - 50 MB

Examples:

• A text only tweet: 140 characters * 2 bytes = 280 bytes
• A tweet with an embedded 2 minute video = 140 characters 2 bytes + 2 50 MB = ~100 MB
• A database record tracking a transaction with the following fields:
  • created_at - 5 bytes
  • product_id - 8 bytes
  • category_id - 4 bytes
  • seller_id - 8 bytes
  • buyer_id - 8 bytes
  • quantity - 4 bytes
  • total_price - 5 bytes
  • Total: 42 bytes
• A database storing 100 million transactions of ~40 bytes = 100,000,000 * 40 = 4,000,000,000 bytes or 4 GB

Sources

• The numbers and date sizing comes from MySQL Data Type Storage Requirements.
• The character and media estimates come from ItsAllBinary
• Stanford also has estimates on sizes.