Understanding DIM Weight: The Complete Guide
Dimensional weight (DIM weight) is one of the most important concepts in shipping. If you're shipping packages for your business, understanding DIM weight can save you hundreds—or thousands—of dollars per year.
Quick Summary: DIM weight pricing charges you based on package size, not just actual weight. Large but light packages often cost more because of DIM weight.
What Is Dimensional Weight?
Dimensional weight (also called volumetric weight or DIM weight) is a pricing technique used by shipping carriers worldwide. It calculates a theoretical weight based on the size of your package, ensuring that large but lightweight shipments are charged fairly for the space they occupy.
Think of it this way: a shipping truck has limited space. A box of feathers takes up as much room as a box of bricks the same size. Without DIM weight pricing, carriers would lose money shipping lightweight but bulky items.
Why Do Carriers Use DIM Weight?
Before the 1990s, most carriers charged purely by actual weight. This created a problem: trucks and planes would fill up with packages before reaching their weight capacity. Carriers introduced dimensional weight to optimize capacity.
- Space is valuable: Vehicles have limited cubic space
- Fair pricing: Bulky items should pay for the space they consume
- Industry standard: All major carriers now use DIM weight
The DIM Weight Formula
The basic formula is straightforward:
DIM Weight = (Length × Width × Height) ÷ DIM Divisor
The DIM divisor varies by carrier and unit system:
| Carrier | Imperial (in³/lb) | Metric (cm³/kg) |
|---|---|---|
| UPS | 139 | 5000 |
| FedEx | 139 | 5000 |
| DHL Express | 139 | 5000 |
| Canada Post (Priority) | 139 | 5000 |
| Canada Post (Regular) | 166 | 6000 |
Billable Weight: The Number That Matters
Carriers compare your package's actual weight to its DIM weight and charge you based on whichever is higher. This result is called the billable weight.
Billable Weight = MAX(Actual Weight, DIM Weight)
Real-World Example
Let's say you're shipping a box of decorative pillows via UPS:
- Box dimensions: 18" × 18" × 12"
- Actual weight: 4 lbs
Step 1: Calculate the Volume
18 × 18 × 12 = 3,888 cubic inches
Step 2: Apply the DIM Divisor
3,888 ÷ 139 = 27.97 lbs (DIM weight)
Step 3: Determine Billable Weight
Since 27.97 lbs > 4 lbs, you'll be charged for 28 lbs (rounded up).
💡 Key Insight
In this example, you're paying for 7× more weight than the package actually weighs! This is why right-sizing your boxes is so important.
How Carriers Round Dimensions
Different carriers use different rounding rules, which can significantly affect your costs:
| Carrier | Dimension Rounding | Weight Rounding |
|---|---|---|
| UPS | Round UP each dimension | Round UP to whole lb |
| FedEx | Round UP each dimension | Round UP to whole lb |
| DHL Express | Standard rounding | Round UP to 0.5 kg |
| Canada Post | Standard rounding | Round UP to 0.5 kg |
UPS and FedEx round UP each dimension. This means a box measuring 12.1" × 10.1" × 8.1" becomes 13" × 11" × 9" for DIM weight calculation—a 25% increase in volume!
When Does DIM Weight Apply?
DIM weight pricing applies to:
- Ground shipments: UPS Ground, FedEx Ground, etc.
- Express shipments: All air services
- International shipments: Virtually all
- Domestic shipments: For most carriers (with some exceptions)
Historically, ground shipments had a minimum package size threshold before DIM weight applied. As of 2015-2017, most carriers removed these thresholds, making DIM weight apply to almost all packages.
Negotiating DIM Factors
If you ship high volumes, you may be able to negotiate a more favorable DIM divisor with your carrier. Common negotiated divisors include:
- 166 (more favorable than 139)
- 194 or 200 (for large shippers)
- 250+ (for very high volume accounts)
A higher divisor means lower DIM weight, which can save significant money on bulky shipments.
Calculate Your DIM Weight
Ready to find out your package's billable weight? Use our free calculator: