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:
- Small Box: $10.60 (vs. $11.70 retail)
- Medium Box: $18.50 (vs. $21.05 retail)
- Large Box: $27.10 (vs. $29.95 retail)
Businesses with high volume can negotiate further discounts via the USPS Business Rate Card or Negotiated Service Agreements.
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 |
- Ship heavy items short or long distances.
- Need predictable costs.
- Want free packaging and zone-free pricing.
When to use weight-based or cubic:
- 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
- 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.
USPS Flat Rate Boxes remain one of the most straightforward and reliable ways to ship packages nationwide with predictable, flat pricing and fast delivery.
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