Frequently Asked Questions About Canada Post Flat Rate Boxes
How much is a Canada Post flat rate box?
As of September 2026 the four sizes are $18.99 extra small, $21.99 small, $24.99 medium and $32.99 large, and that price is per box with postage already included. Canada Post does not publish an effective date for these, so check its flat rate box page for the current figure before you buy. One catch worth knowing: buying online means buying a pack of 12, so an order of extra small boxes is 12 x $18.99 rather than $18.99.
Does the flat rate box price include shipping?
Yes. Canada Post states that postage is included in the cost and that it is not based on destination or weight, up to 5 kg. That is the whole point of the product: one price to anywhere in Canada, with tracking and the on-time delivery guarantee included. You pay for the box and the postage together, then fill it and send it.
Can I put a Canada Post flat rate box in a mailbox?
The two smaller sizes, yes. Canada Post lists the extra small and small boxes as droppable in a street letter box or at a post office, while the medium and large boxes are post office only. If avoiding a trip to the post office matters to you, that is a real reason to choose a smaller box even when the next size up would also fit your item.
What are the Canada Post flat rate box sizes?
Four: extra small at 22.5 x 15.5 x 7.62 cm, small (2026) at 32 x 24 x 8 cm, medium at 37.9 x 26 x 12 cm, and large at 40.3 x 29.8 x 18.7 cm. All four take up to 5 kg. An older small box with different dimensions is still in circulation, so if you are measuring against a box you already have rather than buying new, check it rather than assuming the published figure.
Is a flat rate box cheaper than a regular Canada Post parcel?
Sometimes, and it depends entirely on your parcel. A normal Canada Post quote is built from the rate code for your origin and destination pair, the greater of actual or volumetric weight, and your service. Flat rate ignores all three. So flat rate tends to win on heavy, compact, long-distance parcels, and lose on light parcels travelling a short distance, where a normal quote can come in well under it. Price your actual parcel before buying a pack of 12.
Are Canada Post prepaid labels accepted everywhere in Canada?
No, and the exclusions are worth checking before you buy. Canada Post states prepaid labels are not available for oversized or unpackaged items, for shipments to Nunavut East, Nunavut West, the Northwest Territories or Yukon, for shipments to Air Stage offices, or for prepaid envelopes, which already include shipping. If you ship north, that northern exclusion matters more than anything else on this page.
What is the difference between a regional and a Canada-wide prepaid envelope?
How far it can travel, and the price gap is large. Canada Post sells Xpresspost prepaid envelopes in a regional version at roughly $16 to $23 and a Canada-wide version at roughly $25 to $41, with a similar split on the bubble envelopes and on Priority. Buying Canada-wide for a shipment staying inside your region is close to a 50% overpay on Xpresspost, so match the envelope to the distance. Commercial versions sold in tens cost less per unit again.
What happens if my item does not fit in a flat rate box?
Then flat rate is not the product for it, and forcing the fit is expensive. Over 5 kg or outside the box dimensions you are back to normal parcel pricing, where weight, volumetric equivalent and rate code all apply, and past Canada Post's hard maximums a parcel picks up surcharges instead. See our Canada Post Shipping Rates guide for how a normal quote is built, and Canada Post Surcharges for what oversized and out-of-spec parcels cost.
