Canada Post flat-rate boxes come in extra-small, small, medium and large sizes, with a 5 kg limit. Prepaid envelopes are separate products. Compare the current box price with a quote for your own packaging; neither is always cheaper.
Canada Post box options
A flat-rate box includes postage under its product conditions. Your own packaging needs a separate label priced for the selected service. Prepaid envelopes have their own rules and are not flat-rate box sizes.
| Size | Published dimensions (cm) | Maximum weight |
|---|---|---|
| Extra-small box | 22.5 × 15.5 × 7.62 | 5 kg |
| Small box | 32 × 24 × 8 | 5 kg |
| Medium box | 37.9 × 26 × 12 | 5 kg |
| Large box | 40.3 × 29.8 × 18.7 | 5 kg |
Check the current dimensions before packing. Do not alter the box shape or exceed 5 kg. A compact parcel may fit several options; compare actual totals instead of assuming the flat-rate product wins.
Watch out for dimensional weight
For parcels outside flat-rate, carriers charge the greater of actual weight and dimensional weight (L × W × H ÷ divisor). A large half-empty box can get expensive. Choose the smallest box that protects the contents, and calculate dimensional weight before buying the label.
Where to get boxes
Canada Post flat-rate boxes are available at the post office. For your own packaging, any sturdy box works. Reusing a clean box is free and eco-friendly. Make sure old labels/barcodes are removed or covered.
Compare the rate for YOUR box
Once you've picked and weighed the box, the same parcel can cost very differently by carrier. Rather than assume Canada Post flat-rate is cheapest, compare your box (real weight + dimensions) across several carriers.
Enter your packed dimensions and weight in a quote to compare available services. Confirm the service-specific dimensional-weight divisor and packaging restrictions before purchase.