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Canada Post flat rate boxes are prepaid shipping boxes: one price covers the box and the postage together, anywhere in Canada, up to a 5 kg weight limit. They come in several sizes. Flat rate wins when your item is heavy for its size or going a long distance; for light items or short trips, regular parcel pricing is usually cheaper.
| Feature | How it works |
|---|---|
| Pricing | One flat price per box size; the same whether it goes across town or across the country |
| Weight limit | 5 kg maximum, as long as the box closes properly |
| Sizes | Several sizes from small to large; pick the smallest your item fits in |
| Coverage | Canada-wide; the price does not change with distance |
| Speed | Expedited-level service within Canada |
Flat rate pricing ignores two things regular parcel pricing charges for: weight (up to the limit) and distance. So it wins in exactly the two cases where those matter. A dense, heavy item near the 5 kg limit going from Halifax to Vancouver is the textbook flat rate win: regular parcel pricing would charge for both the weight and the cross-country distance, while the flat rate box charges one price. Small businesses shipping the same heavy product nationwide love flat rate boxes because the shipping cost becomes predictable: one product, one box, one price, every order.
It loses in the mirror-image cases. A light item going a short distance costs less as a regular parcel, because you are paying for what you actually ship instead of the flat rate's built-in average. And an item that does not fit any of the box sizes cannot use flat rate at all: if it fits, it ships, but there is no squeezing an oversized item into a box that will not close. The box has to close flat and tape shut normally; a bulging box that will not seal can be refused.
Buy the box at a post office or online, pack your item, seal it, and attach the included prepaid label or the label that comes with the box purchase. The postage is already paid, so there is no weighing and no zone calculation at the counter: it goes into the stream like any other parcel. Because the price is prepaid, double-check the size before you buy; an unused box is just cardboard you paid postage prices for.
Packing still matters. The box protects against crushing, but the contents can still shift, so fill dead space with crumpled paper. Fragile items need their own cushioning inside the box; the flat rate covers the shipping, not the packing. And the 5 kg limit is firm: if the sealed box weighs more, it cannot go as a flat rate parcel.
LetterAgent sells Canada-only flat-rate Xpresspost labels through a quote-approve-pay flow with your AI assistant: you describe the parcel, approve the exact quoted price, pay once through Stripe, and get a label PDF. Like Canada Post's flat rate boxes, the price does not depend on distance within Canada, and the same 5 kg maximum applies. The difference is the packaging: a LetterAgent label goes on your own box, while a flat rate box bundles the box and the postage together. If you already have boxes and ship often, labels are the flexible route; if you want one purchase that covers box plus postage, the flat rate box is simpler.
Ready to ship it? Get a shipping label with LetterAgent: describe it to your AI assistant, approve the exact quoted price, and get your label.
LetterAgent is a working name. Prices include print, postage, and our service fee. US prices in USD, Canadian prices in CAD (Canadian prices exclude applicable sales tax, added at checkout). Currently in private testing.
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