Overview of USPS Flat Rate Box Shipping Costs
Key Takeaway: USPS Priority Mail Flat Rate boxes offer predictable, zone-free pricing for packages up to 70 lb. Small Flat Rate Boxes ship for $11.70 at retail ($10.60 commercial), and Medium Flat Rate Boxes ship for $21.05 at retail ($18.50 commercial) regardless of weight or distance.
1. What Is Priority Mail Flat Rate Shipping?
Priority Mail Flat Rate is a USPS domestic service that lets customers ship packages in USPS-branded boxes and envelopes at a single flat price, regardless of weight (up to 70 lb) or zone. All Flat Rate packaging is provided free of charge by USPS. Key benefits include:
- Simplified pricing: one rate per box size, nationwide.
- Fast delivery: 2–3 business days to most U.S. locations.
- Up to $100 of included insurance and free USPS Tracking.
- Exemption from nonstandard fees (length, girth, volume) for Flat Rate packaging.
2. Flat Rate Box Sizes and Retail Prices
Below is a summary of the domestic Priority Mail Flat Rate Box options and their retail vs. commercial (online) prices:
(Source: USPS Priority Mail Flat Rate Products)
| Package Type | Retail Price | Commercial Price | Dimensions (External) | Max Weight |
|---|---|---|---|---|
| Small Flat Rate Box | $11.70 | $10.60 | 8 11⁄16″ × 5 7⁄16″ × 1 3⁄4″ | 70 lb |
| Medium Flat Rate Box – Top-Loading (Type 1) | $21.05 | $18.50 | 11 1⁄4″ × 8 3⁄4″ × 6″ | 70 lb |
| Medium Flat Rate Box – Side-Loading (Type 2) | $21.05 | $18.50 | 14″ × 12″ × 3 1⁄2″ | 70 lb |
| Large Flat Rate Box | $29.95 | $27.10 | 12 1⁄4″ × 12 1⁄4″ × 6″ | 70 lb |
| APO/FPO/DPO Flat Rate Box | $28.70 | $25.85 | 12 1⁄4″ × 12 1⁄4″ × 6″ | 70 lb |
| Large Flat Rate Board Game Box | $29.95 | $27.10 | 23 1⁄2″ × 11 1⁄2″ × 3 3⁄4″ | 70 lb |
| Prepaid Forever® Priority Mail Flat Rate Packaging | From $11.00 | N/A | Various | 70 lb |
2.1 Small Flat Rate Box
- Retail: $11.70
- Commercial: $10.60
- Dimensions: 8 11⁄16″ × 5 7⁄16″ × 1 3⁄4″
- Ideal for small electronics, brochures, jewelry.
2.2 Medium Flat Rate Box
USPS offers two medium box shapes at the same price:
- Top-Loading (Type 1) and Side-Loading (Type 2)
- Retail: $21.05
- Commercial: $18.50
- Dimensions:
- Type 1: 11 1⁄4″ × 8 3⁄4″ × 6″
- Type 2: 14″ × 12″ × 3 1⁄2″
- Great for shoes, office supplies, small electronics.
3. How to Ship a Flat Rate Box
- Choose the right Flat Rate box from your local Post Office or order free supplies online.
- Pack your items so the box closes within its normal folds.
- Weigh (optional)-since weight doesn’t affect price (up to 70 lb), weighing is optional.
- Print postage via Click-N-Ship (commercial pricing), at a Post Office, or online.
- Affix the label and drop off at a Post Office or schedule a free pickup.
3.1 Online Discounts
Using Click-N-Ship online grants Commercial pricing:
- Businesses with high volume can negotiate further discounts via the USPS Business Rate Card or Negotiated Service Agreements.
- Small Box: $10.60 (vs. $11.70 retail)
- Medium Box: $18.50 (vs. $21.05 retail)
- Large Box: $27.10 (vs. $29.95 retail)
4. Comparison with Other Priority Mail Options
When to use Flat Rate:
| Service | Pricing Basis | Speed | Packaging Provided | Weight Limit |
|---|---|---|---|---|
| Flat Rate Boxes | Flat price per box | 2–3 days | USPS-branded boxes | 70 lb |
| Priority Mail Weight-Based | By weight and destination zone | 2–3 days | Customer-provided | 70 lb |
| Priority Mail Cubic | By package cubic volume | 2–3 days | Customer-provided | 150 lb DIM |
| First-Class Package Service | By weight (≤ 15.999 oz), zone | 2–5 days | Customer-provided | 16 oz |
| USPS Ground Advantage | By weight and zone (ground delivery) | 2–5 days | Customer-provided | 70 lb |
- When to use weight-based or cubic:
- Ship heavy items short or long distances.
- Need predictable costs.
- Want free packaging and zone-free pricing.
- Ship lightweight or large but light packages where zone-based or cubic pricing is cheaper.
5. International Flat Rate Options
While this overview focuses on domestic shipping, USPS also offers Priority Mail International Flat Rate packaging:
- Small & large boxes up to 20 lb (envelopes up to 4 lb).
- Prices start at $30.90 retail ($29.66 commercial) for envelopes and small boxes.
6. Conclusion and Recommendations
- USPS Flat Rate Boxes remain one of the most straightforward and reliable ways to ship packages nationwide with predictable, flat pricing and fast delivery.
- For consistent, easy pricing on domestic shipments up to 70 lb, choose USPS Priority Mail Flat Rate Boxes.
- Opt for Commercial Prices via Click-N-Ship to save up to ~12% compared to retail rates.
- Select the smallest box that fits your items to avoid overpaying.
- Compare against weight-based and cubic rates for lightweight or nonconforming packages.
