Accurately determining the physical size of a package is the foundational step in preparing any shipment for transit. Precise measurement directly influences the final cost of shipping, ensuring the package qualifies for the quoted rate and avoids unexpected fees or surcharges applied by the carrier. Failing to measure correctly can lead to significant delays, potential rejection of the package at the point of sorting, or unexpected fees. Understanding the proper techniques for calculating dimensions ensures a smooth and predictable shipping process.
Essential Tools and Terminology
The most reliable instrument for obtaining package dimensions is a standard, retractable tape measure or a measuring stick. Shipping measurements rely on three standardized terms: Length, Width, and Height, which define the three-dimensional space the package occupies.
Length is always the longest side of the package’s exterior surface. Width is the second-longest side, measured perpendicular to the length. Height (sometimes referred to as Depth) is the distance between the top and bottom faces of the box. All readings must be taken from the outer edges of the package, including any bulging or protruding labels, to capture the maximum space the package consumes.
Step-by-Step Measurement of a Standard Shipping Box
The process begins by laying the box flat on a surface and identifying the longest side to establish the Length. Place the tape measure at one corner, ensuring the tape is pulled straight along the entire edge to prevent slack that could skew the reading. Record this measurement.
Next, measure the side perpendicular to the Length to define the Width. Maintaining a perpendicular alignment is necessary to avoid measuring diagonally across the face. Pull the tape measure straight across the full width of the box, ensuring it is flat against the surface.
Finally, measure the distance from the base of the box to the highest point of the sealed top flap to determine the Height. The tape must be held perpendicular to the base to capture the true vertical distance, especially if the box is slightly misshapen.
Once all three dimensions are recorded, standard shipping practice is to round each individual measurement up to the nearest whole inch. For example, a box measured at 14.2 inches in Length is recorded as 15 inches. This rounding method accounts for minor variations, bulges, or machine tolerances during automated scanning, establishing the final billable dimensions used by transportation companies.
Calculating Dimensional Weight (DIM Weight)
Accurate measurements are crucial for calculating the package’s billable weight, which is often determined by Dimensional Weight (DIM Weight). Transportation companies use DIM Weight to account for the space a package occupies in a truck or airplane, rather than just its physical mass. The billable weight is always the greater of the package’s actual scale weight or its calculated DIM Weight.
Dimensional Weight is calculated by multiplying the three dimensions (Length x Width x Height) and then dividing that total volume by a specific number known as the DIM Divisor. The formula is expressed as (Length x Width x Height) / DIM Divisor. This calculation yields a weight in pounds that represents the package’s density.
The DIM Divisor is not a universal constant and changes based on the carrier, the service level, and whether the shipment is domestic or international. A common divisor for domestic ground shipments is 166 for dimensions measured in inches. For international or higher-speed air services, a more aggressive divisor, such as 139, is often applied, resulting in a higher DIM Weight for the same package volume.
Shippers must use the divisor provided by their specific carrier and service agreement to obtain the accurate DIM Weight. If the resulting DIM Weight exceeds the actual weight, the shipper will be charged based on the higher dimensional weight. This system incentivizes shippers to use the smallest possible packaging to reduce the billable size.
Measuring Irregular and Non-Box Shapes
Packages that are not standard rectangular boxes require a different approach to determine their billable dimensions. Items like mailing tubes or irregularly shaped custom packaging must still be assigned three dimensions. The general rule for irregular items is the “cubing out” method.
Cubing out involves placing the non-standard item into the smallest possible rectangular box that would completely enclose it. The shipper then measures the Length, Width, and Height of that container. This method ensures the carrier bills for the maximum space the item will occupy within the sorting and transport system.
Mailing tubes are measured by recording the actual length of the tube, end-to-end, as the Length. The Width and Height are calculated using the tube’s Girth, which is the circumference around the outside of the tube. By treating the tube as a square package whose width and height equal the diameter, the carrier can process the circular shape within their cubing system.
Carrier-Specific Measurement Requirements
While measuring Length, Width, and Height follows general principles, specific transportation providers impose unique requirements that affect the final calculation. One common variation is the rounding policy; some carriers mandate rounding up to the next full inch, while others may require rounding up to the nearest half-inch increment. Shippers must consult their specific carrier agreement, as miscalculating the rounding can lead to automatic dimension corrections and fees.
All major carriers enforce maximum size and weight limits that packages cannot exceed. These limits are typically expressed as a maximum combined dimension, such as Length plus Girth, often capped around 130 inches. Packages that exceed these thresholds are classified as “oversize” or “large packages” and trigger substantial surcharges. Exceeding the absolute maximum limit can result in the package being rejected entirely by the carrier network.