Flat Rate Shipping: When It Saves You Money
Flat rate shipping charges one price regardless of weight - perfect for heavy, dense items. Compare all flat rate options and learn when to use them.
When should I use flat rate shipping?
Use flat rate shipping when your package is heavy but fits in a flat rate box. The break-even point is typically around 4-5 lbs for small boxes and 7-10 lbs for medium boxes. USPS Flat Rate boxes are best for dense, heavy items shipping cross-country. If your package is light or shipping locally, weight-based rates are usually cheaper.
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| Carrier | Service | Price | Delivery Time | |
|---|---|---|---|---|
| USPS | Small Flat Rate Box | $9.85 | 1-3 Days | |
| USPS | Medium Flat Rate Box | $17.10 | 1-3 Days | |
| USPS | Large Flat Rate Box | $22.45 | 1-3 Days | |
| USPS | Padded Flat Rate Envelope | $9.45 | 1-3 Days | Cheapest |
| USPS | Legal Flat Rate Envelope | $8.70 | 1-3 Days | |
| USPS | Regional Rate Box A | $10.20-14.50 | 1-3 Days |
Small Flat Rate Box
Medium Flat Rate Box
Large Flat Rate Box
Padded Flat Rate Envelope
Legal Flat Rate Envelope
Regional Rate Box A
* Prices shown are discounted ShipWave rates. Actual rates vary by exact dimensions, weight, and origin/destination.
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Understanding USPS Flat Rate Shipping
USPS Priority Mail Flat Rate charges one price regardless of weight (up to 70 lbs) or destination. The price only depends on the box or envelope size you choose:
Flat Rate Envelopes:
- Legal Flat Rate Envelope - $8.70 (15" x 9.5")
- Padded Flat Rate Envelope - $9.45 (12.5" x 9.5")
Flat Rate Boxes:
- Small Flat Rate Box - $9.85 (8.6" x 5.4" x 1.6")
- Medium Flat Rate Box - $17.10 (11" x 8.5" x 5.5" OR 13.6" x 12" x 3.4")
- Large Flat Rate Box - $22.45 (12" x 12" x 5.5")
Boxes are free from USPS - order online or pick up at any post office.
When Flat Rate Beats Weight-Based
Flat rate saves money in specific situations:
- Heavy packages - The heavier the package, the more you save. A 20 lb package in a Medium Flat Rate Box ($17.10) would cost $30+ at weight-based rates.
- Cross-country shipments - Weight-based rates increase with distance. Flat rate is the same coast to coast.
- Dense items - Small but heavy items like books, tools, or hardware maximize flat rate value.
- Jewelry and coins - Heavy metals ship cheaply in padded flat rate envelopes.
When to avoid flat rate:
- Light packages under 3-4 lbs (weight-based is cheaper)
- Regional shipments (USPS Ground Advantage or Regional Rate often wins)
- Oddly shaped items that do not fit standard boxes
Regional Rate: The Middle Ground
USPS Regional Rate boxes are a hybrid between flat rate and weight-based pricing. The price varies by distance zone but is often cheaper than standard flat rate for regional shipments:
Regional Rate Box A: Similar size to Small Flat Rate. Prices range from $10.20 (zone 1-2) to $14.50 (zone 8).
Regional Rate Box B: Similar size to Medium Flat Rate. Prices range from $12.85 (zone 1-2) to $18.60 (zone 8).
When to use Regional Rate: Shipping heavy packages to nearby zones (1-5). Compare Regional Rate to standard Flat Rate - for zones 1-4, Regional Rate often wins.
When to use Flat Rate: Shipping to far zones (6-8) where flat rate price is lower than zone-based Regional Rate.
Pro Tips to Save More
Know Your Break-Even Weights
Small Flat Rate: ~4-5 lbs. Medium Flat Rate: ~7-10 lbs. Large Flat Rate: ~10-15 lbs. Below these, weight-based is cheaper.
Order Free Boxes Online
USPS delivers free Priority Mail Flat Rate boxes to your door. Order at usps.com/ship. Stock up to always have options.
Use Padded Envelopes for Small Heavy Items
The $9.45 padded flat rate envelope is perfect for jewelry, coins, small electronics, or small books.
Compare Regional Rate for Nearby Zones
For zones 1-4, Regional Rate boxes often beat Flat Rate prices. Check both options before shipping.
Consider Two Medium Boxes
For very heavy shipments, two Medium Flat Rate boxes ($34.20) may be cheaper than one Large ($22.45) plus weight-based.
If It Fits, It Ships
You can ship up to 70 lbs in a flat rate box. Pack it full to maximize value - there is no weight penalty.
Use Flat Rate for Returns
Include a prepaid flat rate return label in shipments. Predictable cost regardless of what customers send back.
Frequently Asked Questions
- USPS Flat Rate boxes have a 70 lb weight limit. You can ship any weight up to 70 lbs for the same price. This makes flat rate extremely valuable for heavy, dense packages that fit in the standard box sizes.
- Yes, USPS Priority Mail Flat Rate boxes and envelopes are free. You can order them online at usps.com/ship for free delivery to your address, or pick them up at any post office. You must use them for Priority Mail shipments.
- Flat rate becomes cheaper when your package exceeds the break-even weight: roughly 4-5 lbs for Small Flat Rate, 7-10 lbs for Medium, and 10-15 lbs for Large boxes. It also saves money for cross-country shipments where zone-based pricing adds up.
- No, you must use official USPS Flat Rate boxes or envelopes to get flat rate pricing. Using your own box means you will be charged weight-based Priority Mail rates. The boxes are free, so there is no cost benefit to using your own.
- UPS offers Simple Rate for packages up to 50 lbs with three price tiers based on box size (XS, S, M). FedEx One Rate is similar, with pricing based on package size. Both are typically more expensive than USPS Flat Rate but may have advantages for specific shipments.
- Flat Rate is the same price regardless of destination zone. Regional Rate prices vary by zone - cheaper for nearby zones (1-4), potentially more expensive for far zones (6-8). Compare both for your specific route.
- Yes, USPS offers Priority Mail International Flat Rate boxes and envelopes. Prices vary by destination country. International Flat Rate can be very economical for heavy packages, though customs and import fees may apply.
- USPS Priority Mail Flat Rate delivers in 1-3 business days domestically. It is the same Priority Mail service level - the only difference is how the price is calculated (box size vs weight).
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