What is dimensional weight?
Dimensional weight, commonly known as DIM weight or volumetric weight, is a pricing method used by shipping carriers to account for packages that take up a lot of space but weigh relatively little. Instead of charging solely by how heavy a package is, carriers calculate a theoretical weight based on the package's volume. If that theoretical weight exceeds the actual weight on the scale, the carrier charges based on the DIM weight instead.
This pricing model exists because carrier vehicles and aircraft have both weight limits and space limits. A truck full of pillows would reach its volume capacity long before it reaches its weight limit. Without DIM weight pricing, the carrier would lose revenue hauling large, lightweight shipments because the space those packages occupy could have been filled with denser, heavier freight generating higher charges.
DIM weight pricing was introduced by major carriers in the early 2000s and has since become standard across the industry. FedEx, UPS, and USPS all use DIM weight calculations, though each carrier applies a different divisor (called a DIM factor) to convert cubic inches into pounds. Understanding how DIM weight works is essential for anyone who ships packages regularly, whether you run an e-commerce business, manage a warehouse, or just need to send a large gift.
The key takeaway is simple: carriers always bill you for whichever is greater, the actual weight or the DIM weight. If your package is compact and heavy, actual weight determines the charge. If your package is large and light, DIM weight takes over, and your shipping costs may be significantly higher than you expect.
How DIM weight is calculated
**Formula:** \`\`\` DIM Weight (lbs) = (Length x Width x Height in inches) / DIM Factor \`\`\`
The calculation is straightforward. Multiply the three package dimensions together to get the cubic size in cubic inches. Then divide by the carrier's DIM factor to convert that volume into an equivalent weight in pounds. The result is always rounded up to the next whole number.
**Example:** A box measuring 24 x 18 x 16 inches with an actual weight of 10 lbs: - Cubic size: 24 x 18 x 16 = 6,912 cubic inches - FedEx/UPS DIM weight: 6,912 / 139 = 49.7, rounded up to **50 lbs** - USPS DIM weight: 6,912 / 166 = 41.6, rounded up to **42 lbs** - Billable weight at FedEx/UPS: **50 lbs** (DIM weight exceeds actual weight) - Billable weight at USPS: **42 lbs** (DIM weight still exceeds actual weight)
In this example, even though the package only weighs 10 lbs on the scale, every carrier bills as if it weighs 42 to 50 lbs because the box occupies so much space.
For metric measurements, convert centimeters to inches (divide by 2.54) and kilograms to pounds (multiply by 2.20462) before applying the formula. This calculator handles the conversion automatically when you select metric units.
DIM factors by carrier
Each carrier uses a specific divisor called a DIM factor. A lower DIM factor produces a higher DIM weight, meaning more packages will be billed by volume rather than scale weight.
- **FedEx:** DIM factor of 139 for all domestic and international shipments (Ground, Express, Home Delivery) - **UPS:** DIM factor of 139 for all domestic and international services (Ground, Air, SurePost) - **USPS:** DIM factor of 166 for Priority Mail packages exceeding 1 cubic foot (1,728 cubic inches). Priority Mail Express and other services may differ.
Because USPS uses a higher DIM factor (166 vs 139), its DIM weight calculation is more forgiving for shippers. A package that triggers DIM weight surcharges at FedEx or UPS may still be billed by actual weight at USPS. This makes USPS Priority Mail particularly attractive for lightweight, bulky items.
Note that DIM factors are standard industry values, not pricing. They represent the mathematical divisor used in the volumetric weight formula. Actual shipping rates depend on the billable weight, service level, origin, destination, and any negotiated discounts.
How to use this calculator
1. Select your unit system: imperial (inches and pounds) or metric (centimeters and kilograms) 2. Enter your package dimensions: length, width, and height 3. Enter the actual weight of the package as measured on a scale 4. Review the results, which appear automatically as you type
The calculator shows the DIM weight for each carrier side by side, highlights which weight the carrier will bill, and tells you whether you are being charged by actual weight or DIM weight. A warning appears if any carrier will use DIM weight, along with a suggestion to optimize your packaging.
Tips to reduce DIM weight charges
- **Right-size your boxes.** Use the smallest box that safely fits your product with adequate padding. A box that is even a few inches too large in each dimension can dramatically increase DIM weight. - **Eliminate void fill.** Excessive bubble wrap, packing peanuts, or air pillows increase box size without adding product. Use fitted inserts or molded pulp trays to hold items snugly. - **Consider poly mailers.** For soft goods like clothing, poly mailers conform to the product shape and eliminate the rigid box dimensions that drive up DIM weight. - **Use custom packaging.** If you ship the same product repeatedly, invest in custom-sized boxes. The upfront cost is often offset by lower shipping charges over time. - **Compare carriers.** Because USPS uses a higher DIM factor (166), packages that trigger DIM charges at FedEx or UPS may still be billed by actual weight through USPS Priority Mail. - **Negotiate your DIM factor.** High-volume shippers can often negotiate a higher DIM factor (such as 166 or 200) with FedEx and UPS, reducing DIM weight charges across all shipments. - **Disassemble when possible.** Ship furniture or equipment disassembled in flat boxes rather than assembled in oversized cartons.
FAQs
Q: What is a DIM factor? A: A DIM factor is the divisor used to convert a package's cubic size (in cubic inches) into an equivalent weight (in pounds). FedEx and UPS use 139; USPS Priority Mail uses 166. A higher DIM factor is more favorable to the shipper because it produces a lower DIM weight.
Q: Why is my shipping charge based on DIM weight? A: Carriers charge based on whichever is greater: your package's actual weight or its DIM weight. If your box is large relative to how much it weighs, the DIM weight exceeds the actual weight, and the carrier uses DIM weight to determine your rate. This happens most often with lightweight products shipped in oversized boxes.
Q: How can I reduce dimensional weight? A: The most effective strategy is using a smaller box. Even reducing each dimension by 2 inches can significantly lower DIM weight. Other approaches include switching to poly mailers for soft goods, eliminating excessive void fill, and comparing carriers since USPS has a more forgiving DIM factor than FedEx or UPS.
Q: Does USPS always use DIM weight? A: No. USPS only applies DIM weight pricing to Priority Mail packages that exceed 1 cubic foot (1,728 cubic inches). Smaller Priority Mail packages and First-Class Package Service are billed by actual weight only.
Q: Are DIM factors the same for domestic and international shipments? A: FedEx and UPS both use a DIM factor of 139 for domestic and international shipments. USPS uses 166 for Priority Mail domestically. International services may have different factors depending on the carrier and service level.
Q: What happens if DIM weight and actual weight are equal? A: The carrier bills at that weight. There is no surcharge or penalty for the weights being equal. The carrier simply uses whichever is higher, so when they match, the result is the same either way.
Explore Similar Tools
Explore more tools like this one:
- Shipping Cost Comparison — Compare shipping costs across carriers to find the best... - Container Loading Calculator — Estimate how many boxes fit in a shipping container or... - Freight Class Calculator — Calculate NMFC freight class based on density,... - Adjusted Body Weight Calculator — Calculate ideal and adjusted body weight for dosing... - Aquarium Tank Weight Calculator — Calculate total aquarium weight including water,...