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The Post Office counter charges the highest price there is for a label. Shipping software gets the commercial price for the same box. Type in both and see what the gap is worth over a year.
Retail is the price on the wall at the Post Office. Commercial is the price USPS gives anyone who buys the label through software. Free tools like Pirate Ship pass that price through; Shopify Shipping and Shippo do the same job inside a bigger tool.
The gap on the published example is $2.71 on an 8 oz box going across the country, about 29% less. Lighter boxes and closer zones have a smaller gap; heavier boxes and farther zones a bigger one.
Numbers change. USPS updates prices a few times a year. The example is from the April 26 2026 price list. Always check your own two numbers.
Not sure whether to ship it yourself? The Fulfillment Picker. When does a warehouse pay off? The 3PL Crossover.