Standard Carrier Shipping Boxes
Shipping, Boxes & Logistics · 8 specs
Direct Answer
Standard parcel carriers (USPS, FedEx, UPS) define standardized rigid carton tiers, flat rate boxes, and dimensional weight divisor formulas (e.g. Length × Width × Height ÷ 139) that determine billable freight charges across domestic and international logistics networks.
Source: USPS DMM / FedEx Service Guide / UPS Rate & Service Guide Standards · Last reviewed Aug 28, 2026
Specs
| Governing Standards | USPS Domestic Mail Manual / FedEx Express / UPS Ground Standards |
| USPS Small Flat Rate Box | 8-11/16" × 5-7/16" × 1-3/4" (22.1 × 13.8 × 4.4 cm) | Max 70 lbs (31.8 kg) |
| USPS Medium Flat Rate (Side) | 11-1/4" × 8-3/4" × 6" (28.6 × 22.2 × 15.2 cm) | Top-loading standard carton |
| USPS Medium Flat Rate (Top) | 14" × 12" × 3-1/2" (35.6 × 30.5 × 8.9 cm) | Shallow wide footprint for clothing/books |
| USPS Large Flat Rate Box | 12-1/4" × 12-1/4" × 6" (31.1 × 31.1 × 15.2 cm) | Max 70 lbs domestic |
| FedEx Small / Medium / Large Box | Small: 12.25×10.9×1.5" | Medium: 13.25×11.5×2.38" | Large: 17.5×12.38×3" |
| Standard Dimensional Weight Divisor | DIM Divisor = 139 (Domestic Commercial & International) | DIM Wt (lbs) = (L × W × H in inches) ÷ 139 |
| Maximum Standard Parcel Size | Maximum Length: 108" (274 cm) | Maximum Length + Girth: 130" (UPS/FedEx Ground) or 165" (Freight) |
USPS Priority Mail Flat Rate Box Dimensions & Interior Volumes
| USPS Flat Rate Box Tier | Interior Dimensions (Inches) | Interior Dimensions (cm) | Interior Volume (Cubic Inches) | Maximum Allowed Weight |
|---|---|---|---|---|
| Small Flat Rate Box | 8-11/16" × 5-7/16" × 1-3/4" | 22.1 × 13.8 × 4.4 cm | ~82 cu in (1.3 L) | 70 lbs (31.8 kg) |
| Medium Flat Rate (Side Load) | 11-1/4" × 8-3/4" × 6" | 28.6 × 22.2 × 15.2 cm | ~590 cu in (9.7 L) | 70 lbs (31.8 kg) |
| Medium Flat Rate (Top Load) | 14" × 12" × 3-1/2" | 35.6 × 30.5 × 8.9 cm | ~588 cu in (9.6 L) | 70 lbs (31.8 kg) |
| Large Flat Rate Box | 12-1/4" × 12-1/4" × 6" | 31.1 × 31.1 × 15.2 cm | ~900 cu in (14.7 L) | 70 lbs (31.8 kg) |
| APO/FPO Military Large | 12-1/4" × 12-1/4" × 6" | 31.1 × 31.1 × 15.2 cm | ~900 cu in (14.7 L) | 70 lbs ($1.50 discount) |
Dimensional Weight (DIM) & Girth Calculation Rules
-
Dimensional Weight (DIM) Formula: If a package is lightweight but bulky, carriers charge based on volumetric weight:
DIM Weight (lbs) = (Length × Width × Height in inches) ÷ 139 -
Length and Girth Rule: Girth equals distance around the thickest part:
Girth = 2 × (Width + Height). Packages exceeding 130 inches total (Length + Girth) incur steep oversize surcharge penalties.