USPS Cubic Pricing Calculator
Find your Priority Mail Cubic and USPS Ground Advantage Cubic tier for boxes and soft packs, under the rules in force since July 12, 2026.
Your numbers
Your result · updates as you type
Your cubic pricing tier
Tier 0.4
12 × 9 × 6.25 in after rounding each side down to the nearest ¼ in = 675 cubic inches = 0.391 cubic feet. Priority Mail Cubic and USPS Ground Advantage Cubic both price it at tier 0.4.
- Cubic feet
- 0.391
- Priority Mail Cubic
- Tier 0.4
- Ground Advantage Cubic
- Tier 0.4
Cubic prices depend on tier and zone, not weight, so any weight up to 20 lb costs the same. To drop to tier 0.3, the height would need to be 4.75 in or less, with the other sides unchanged.
Breakdown
- Measured
- 12.1 × 9.1 × 6.3 in
- Rounded down to ¼ inch
- 12 × 9 × 6.25 in
- Volume
- 675 cubic inches ÷ 1,728 = 0.391 cu ft
- Without rounding down
- 0.401 cu ft (would be tier 0.5)
- Weight
- 9 lb (limit 20 lb)
- Longest side
- 12.1 in (limit 22 in)
- Priority Mail Cubic
- Tier 0.4 (up to 0.5 cu ft)
- USPS Ground Advantage Cubic
- Tier 0.4 (up to 1 cu ft)
How the cubic tier is worked out
Cubic pricing charges by size tier and zone instead of by weight. For boxes, round each side down to the nearest ¼ inch, multiply them, and divide by 1,728 to get cubic feet. The tier is the next 0.1 cubic foot at or above that. For soft packs and padded envelopes, round the length and width down to the nearest ¼ inch and add them; thickness doesn't count.
Example
- Measured
- 12.1 × 9.1 × 6.3 in
- Rounded down to ¼ in
- 12 × 9 × 6.25 in
- Volume
- 675 cubic inches ÷ 1,728 = 0.391 cubic feet
- Weight
- 9 lb
0.391 cubic feet is tier 0.4 for both Priority Mail Cubic and USPS Ground Advantage Cubic. Without rounding down it would be 0.401 cubic feet, a tier higher. To reach tier 0.3, the height would need to be 4.75 in or less.
| Tier | Boxes (cubic feet) | Soft packs (length + width) |
|---|---|---|
| 0.1 | Up to 0.10 | Up to 21 in |
| 0.2 | Over 0.10, up to 0.20 | Over 21 in, up to 27 in |
| 0.3 | Over 0.20, up to 0.30 | Over 27 in, up to 31 in |
| 0.4 | Over 0.30, up to 0.40 | Over 31 in, up to 34 in |
| 0.5 | Over 0.40, up to 0.50 | Over 34 in, up to 36 in |
| 0.6 to 1.0 | USPS Ground Advantage only, in 0.1 steps up to 1.00 | Not available |
Who qualifies, and what changed in July 2026
- Weight: 20 lb or less. Up to that, weight doesn't change the price.
- Size: Priority Mail Cubic goes up to 0.5 cubic foot and USPS Ground Advantage Cubic up to 1 cubic foot.
- Longest side: 22 in or less. USPS raised this from 18 in on July 12, 2026.
- Soft packs: length plus width up to 36 in. Since July 12, 2026, Ground Advantage uses the same five soft pack tiers as Priority Mail, down from ten.
- Not eligible: rolls and tubes. Pleated or expandable mailers are measured like boxes.
- Who can buy it: commercial customers, such as users of USPS-approved PC Postage and label software, and permit imprint mailers.
Some help pages still showed the old 18 in limit in September 2026, including Shopify's USPS page. The Domestic Mail Manual is the rule.
The calculator doesn't show postage, because prices change by zone and at every USPS price change. Look up your tier's price in your label software or USPS Notice 123, then switch on Compare with the price by weight to see which is cheaper.
Using cubic pricing in Shopify and WooCommerce
- 01
Shopify
Shopify Shipping's USPS labels include cubic pricing for packages, soft packs and padded envelopes. Save your real boxes and mailers in Settings → Shipping and delivery → Packages, using the Soft pack type for poly mailers, so labels are rated on accurate sizes.
- 02
WooCommerce
WooCommerce doesn't buy postage itself. Use a label service or plugin that sells commercial USPS postage with cubic pricing, and enter accurate box sizes for each package.
- 03
Design boxes to the tier
A box that sits just over a tier line pays for the higher tier on every label. The result shows how much you'd need to trim to drop a tier.
Questions people ask
What is USPS cubic pricing?
Commercial pricing for Priority Mail and USPS Ground Advantage that charges by a parcel's size tier and zone instead of its weight, for parcels up to 20 lb.
What is the maximum size for cubic pricing?
0.5 cubic foot for Priority Mail Cubic and 1 cubic foot for Ground Advantage Cubic, with the longest side no more than 22 in (since July 12, 2026) and a weight of 20 lb or less.
How do you calculate cubic feet for USPS?
Round each side down to the nearest ¼ inch, multiply length × width × height, and divide by 1,728. For soft packs, add the rounded length and width instead.
When is cubic cheaper than normal postage?
Usually for small, heavy parcels, because the price stays the same up to 20 lb. For a large, light parcel, the weight-based price can be lower, so compare both for your zone.
Do padded envelopes get cubic pricing?
Yes. Soft packs and padded envelopes are tiered by length plus width, up to 36 in, not by volume. Expandable (pleated) mailers are measured like boxes.
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Last reviewed 30 September 2026.
Sources: USPS Domestic Mail Manual 223: Priority Mail Commercial prices (1.3 Cubic) · USPS Domestic Mail Manual 283: USPS Ground Advantage Commercial prices (1.3 Cubic) · USPS Notice 123: Price List · Federal Register: Domestic Competitive Products Pricing and Mailing Standards Changes (May 15, 2026)