Postage Calculator
Estimate USPS postage costs from package weight, dimensions, and destination type.
Returns First Class, Priority Mail, and Media Mail rate comparisons.
Postage cost estimation depends on weight, size (dimensions), mail class (speed of delivery), destination (domestic vs. international), and any add-on services. Understanding these factors helps avoid overpaying at post offices and enables accurate cost forecasting for businesses.
US Postal Service (USPS) rate structure (2024 approximate):
First-Class Mail (letters/flats):
- Letter (up to 3.5 oz): First ounce $0.68 + $0.24 per additional ounce
- Large envelope/flat (up to 13 oz): First ounce $1.39 + $0.24 per additional ounce
- Maximum weight for First-Class: 13 oz (above = Priority Mail)
Priority Mail (2–3 business days):
- Starts at ~$9.25 for packages up to 1 lb (flat rate zones 1–4)
- Flat rate boxes: Small (
$10.40), Medium ($17.25), Large (~$23.95) — regardless of weight up to 70 lbs - Break-even vs. flat rate: calculate at your specific zone
USPS Ground Advantage (formerly Parcel Select Ground):
- Economical for 1–70 lb packages
- Starts at ~$5.25 for 1 lb, Zone 1–4
International — USPS First-Class International:
- Documents/small packets up to 4 oz: $1.55–$3.75 depending on destination
- Priority Mail International: ~$42–$85 for packages
Size-based pricing rules — surcharges apply for:
- Oversize (USPS): Length > 22 inches or girth + length > 108 inches → surcharge
- Non-machinable surcharge: $0.40 extra for letters that are rigid, odd-shaped, or have clasps
Dimensional weight (DIM weight) — for commercial carriers (UPS/FedEx): DIM Weight (lbs) = (L × W × H in inches) ÷ 139
Carrier charges the greater of actual weight or DIM weight. Large, light packages are priced by DIM weight. Example: A box 18″ × 14″ × 12″ = 3,024 cubic inches ÷ 139 = 21.8 lbs DIM weight. If actual weight is 8 lbs, you pay for 22 lbs.
Worked example: Sending a 6 oz letter-sized envelope domestically (US) via First-Class Mail:
- First ounce: $0.68
- Additional 5 oz: 5 × $0.24 = $1.20
- Total postage: $1.88
Sending a 5 lb package across the country (Zone 8):
- USPS Priority Mail: ~$28.50
- USPS Ground Advantage: ~$16.75
- UPS Ground: ~$18.20 (after DIM weight check — actual weight applies if box is small)
- Cheapest option for non-urgent shipment: USPS Ground Advantage at $16.75