Canada Post Flat Rate Boxes

What Canada Post Flat Rate Boxes Are

A flat rate box is a Canada Post box with the postage already paid for. You buy the box, fill it, and send it, and the price does not move whether it goes across town or across the country, for anything up to 5 kg that fits inside.

Tracking and the on-time delivery guarantee are included as well. The catch is that a fixed price is only a good price for some parcels, so this page gives you the numbers and then the honest answer on when flat rate wins. For how a normal Canada Post quote is built instead, see our Canada Post Shipping Rates guide.

Source: Canada Post: Flat rate boxes

Box Sizes and Costs

Four sizes, all capped at 5 kg. The drop off row is the one most people miss, and it can matter more than the price difference.

The extra small and small boxes can go straight into a street letter box. The medium and large cannot, and have to be dropped at a post office. So if your item fits either size, the smaller one does not just cost less, it saves you the trip and the queue entirely. That is worth checking before you default to the next size up for a bit of extra room.

Two notes on the numbers. Prices are per box, with postage included, but buying online means buying a pack of 12, so an order of extra small boxes is 12 times $18.99 rather than $18.99. And Canada Post publishes no effective date against these figures, so treat them as current rather than fixed and check the flat rate box page or the Canada Post store before you order.

One more practical warning: an older small box with different dimensions is still in circulation. If you are measuring an item against a box you already have rather than one you are about to buy, measure the box rather than trusting the published figure.

The large box is not stocked everywhere. Canada Post states it "is not available at all Canada Post locations but can be requested at the post office", so if your item only fits the large box it is worth asking before making the trip.

Source: Canada Post: Flat rate boxes

How to Buy and Ship a Flat Rate Box

Three steps, and each one has a detail that trips people up.

1

Buy a box

Buy a single box at any post office across Canada, or a 12 pack online. Twelve is the online minimum, not the minimum overall, so you do not need a pack to send one parcel.

2

Pack it, without reshaping it

Pack the box without changing its dimensions or shape, and secure the contents. Keep it under 5 kg: Canada Post states that overweight boxes will not be shipped, so this is a refusal rather than a surcharge.

3

Address and send it

Ship from any post office, or drop an extra small or small box into a street letter box. Note that the delivery standard period starts when the box is first scanned, so a box sitting in a letter box has not started its clock yet.

The scanning point deserves emphasis, because it cuts against the convenience of the letter-box drop. The delivery standard period starts when the box is first scanned, not when you post it. Drop a box into a street letter box on a Friday evening and the clock does not begin until it is collected and scanned, which on top of Canada Post's business-day counting can add real time. If a date matters, take it to a post office.

Source: Canada Post: Flat rate boxes

What Is Included, and What You Cannot Add

Every flat rate box comes with:

• Prepaid postage, with no destination or weight variable up to 5 kg
• Tracking and the on-time delivery guarantee, which Canada Post notes varies by destination
• Up to $100 of liability coverage for loss or damage
• Carbon-neutral shipping

Then the part that matters more, and that most coverage of flat rate boxes leaves out. Canada Post states that "no additional features and options can be added such as additional liability, coverage or signature." In practice that means:

• Additional liability coverage. Coverage is capped at $100 and cannot be topped up, where a normal parcel can be insured at $2.75 per additional $100 up to $5,000
• Signature on delivery. Not purchasable on a flat rate box at all, where it costs $2.00 on a normal parcel
• Any other option. Canada Post states plainly that no additional features and options can be added

So if the contents are worth more than $100, a flat rate box is the wrong product. There is no way to insure above the included coverage and no way to require a signature on delivery. On a normal parcel both are available, as our Canada Post Surcharges guide sets out. That single constraint decides the product for a lot of shipments, and it is worth checking before buying a pack of twelve.

Source: Canada Post: Flat rate boxes

Prepaid Envelopes, and the Regional Trap

Alongside the boxes, Canada Post sells prepaid envelopes on the same principle: buy the envelope, the postage is inside the price. The difference is that envelopes come in two coverage versions, and picking the wrong one is an expensive, silent mistake.

Match the envelope to the distance. If most of what you send stays inside your region, buy regional envelopes and keep a few Canada-wide ones for the exceptions. If you ship regularly, the commercial versions sold in packs of ten work out cheaper per envelope again.

These are retail store prices with no effective date attached, so check the Canada Post store for the current figures.

Source: Canada Post store: flat rate and prepaid products

Where Prepaid Labels Are Not Accepted

This is the part worth reading before you buy anything, because it is a hard no rather than a surcharge. Canada Post states that prepaid labels are not available for:

• Oversized or unpackaged items
• Shipments to Nunavut East, Nunavut West, the Northwest Territories and Yukon
• Shipments to Air Stage offices
• Prepaid envelopes, which already include the cost of shipping

Source: Parcel Services Customer Guide, effective 29 May 2026

When Flat Rate Beats a Normal Quote

A flat price is not automatically a good price. Because flat rate ignores distance, weight and volumetric equivalent, it wins in exactly the situations where those three would have worked against you, and loses where they would have worked in your favour.

The honest test is arithmetic rather than instinct: price the parcel you actually ship most often both ways, once as a flat rate box and once as a normal quote, and buy the pack of 12 only if flat rate wins. Buying twelve boxes for a parcel profile that a standard quote handles more cheaply is the common mistake here.

Sources

All sizes, weight limits, drop-off rules and prices on this page are sourced from official Canada Post documentation. Canada Post publishes no effective date against the prices, so confirm before ordering. Last updated: September 30, 2026.

• Canada Post: Flat rate boxes, including the "Box sizes and costs" table. canadapost-postescanada.ca
• Canada Post store: flat rate and prepaid products. store.canadapost-postescanada.ca
• Parcel Services Customer Guide, effective May 29, 2026, on prepaid label exclusions. canadapost-postescanada.ca