Skip to main content
Calculator Daily

Compare Shipping Boxes Calculator

Check which of two boxes fits your item and leaves less empty space. Optionally compare estimated billable weights using each finished parcel’s measurements.

Enter decimal numbers without commas or units. Lengths: equivalent of 0.000001 to 1,000,000 cm; packed weights: equivalent of 0.000001 to 1,000,000 kg. Clearance may be zero. Divisor: 0.000001 to 1,000,000 in its displayed units.

Changing setup converts measurements and reloads its example weight rules.

Item’s outside dimensions (in)

Added on both sides of every axis. Blank means zero. Choose the allowance for your packing method.

Box A

Usable inside dimensions (in)

Box B

Usable inside dimensions (in)

Which box should you use?

Enter the item and both usable inside box sizes. Results update automatically; blank clearance means zero.

Reset clears measurements; your unit setup and weight rules are retained.

The smaller box is useful only if the item and its packing allowance fit. This calculator tests fit first, then compares inside volume. If you enter outside dimensions and packed weights, it can compare estimated billable weights under one shared rule.

How to compare the two boxes

  1. Measure the item’s outside dimensions and choose any clearance per side. Enter the usable inside dimensions of both boxes.
  2. Read the fitting orientation and remaining space. A failed box is excluded from the recommendation, even if its total volume looks sufficient.
  3. For a weight comparison, enter each fitting box’s finished outside dimensions and actual packed weight. Check the shared divisor and rounding settings, then compare the estimates.

How fit and weight are checked

Each rotated item dimension needs item dimension + 2 × clearance per side. An orientation passes only when all three requirements fit within the corresponding inside box dimensions. All six assignments of item length, width, and height are tested; a fitting orientation with the most room on its tightest axis is shown.

When weight comparison is off, the smaller fitting inside volume wins. Empty-volume percentage is 100 × (1 − item volume ÷ inside box volume); it does not measure the amount of packing material to buy.

When weight comparison is on, each outside dimension is rounded according to your setting. Raw dimensional weight = rated outside length × width × height ÷ divisor. Both dimensional and actual packed weight are rounded upward by the selected weight increment, if enabled. Estimated billable weight is the greater of those two values. Each fitting box needs its own packed weight before a weight winner is selected.

Two worked examples

A large volume that still does not fit

An item is 10 × 8 × 4 inches with 0.5 inch clearance per side. Its required envelope is 11 × 9 × 5 inches, or 495 in³. A box measuring 12 × 10 × 4.9 inches inside has 588 in³, yet fails every tested orientation: its shortest side is less than the required 5 inches. Volume alone would give the wrong decision.

The larger box has lower billable weight

For that same item, Box A measures 11 × 9 × 5 inches inside and 11.5 × 9.5 × 5.5 outside; its packed weight is 8.2 lb. Box B measures 12 × 10 × 6 inside and 12.5 × 10.5 × 6.5 outside; its packed weight is 5.1 lb. These are hypothetical measurements.

With divisor 139 and upward whole-inch and whole-pound rounding, A uses 12 × 10 × 6 ÷ 139 ≈ 5.1799 lb, rounded to 6 lb DIM. Its actual weight rounds to 9 lb, so its estimated billable weight is 9 lb. B uses 13 × 11 × 7 ÷ 139 ≈ 7.2014 lb, rounded to 8 lb DIM; its actual rounds to 6 lb. B’s estimate is 8 lb. The larger box wins the weight comparison, but the final price still depends on the carrier’s actual quote.

Before choosing a winner

Use inside dimensions for fit and outside dimensions for dimensional weight. Enter the same axes consistently; the outside size cannot be less than the corresponding inside size. Packed weights can differ because the boxes and packing materials differ. A tight geometric fit does not establish adequate protection or easy closure. Thresholds, prices, surcharges, box strength, and minimum billable weights are outside this model.

Frequently asked questions

Why do I need inside and outside box dimensions?
Usable inside dimensions decide whether the item fits. Finished outside dimensions determine the volume used for dimensional weight. Enter matching length, width, and height axes for each box.
Does a smaller box always have lower billable weight?
No. A smaller outside box can have a lower dimensional weight yet a higher actual packed weight. When actual weight controls, a larger, lighter packed box may have the lower estimated billable weight.
Can I compare shipping weights without both packed weights?
The tool waits for every fitting box’s packed weight before choosing a weight winner. It does not compare one box’s known billable weight with the other box’s dimensional weight alone. You can turn off weight comparison to compare fit and inside volume.
Can I use a volume comparison to prove fit?
No. The calculator first checks the three inside dimensions against all six right-angle item orientations, including your clearance. Empty-volume percentage is shown only for boxes that pass that fit test.
Is the recommended box the cheapest option?
The result identifies the smaller fitting box or the lower estimated billable weight, depending on your chosen comparison. It does not apply shipping prices, service thresholds, surcharges, minimum billable weights, or packaging costs.

Sources and measurement guidance

The Uline box guide distinguishes inside dimensions from outside shipping measurements. FedEx’s dimensional-weight guidance illustrates unit-specific divisors and dimension rounding. Confirm the current rule for your exact service; the loaded settings are examples.

Related packing decisions

Use the Shipping Box Size Calculator if neither box works. Use the Shipping Box Fit Calculator for a detailed single-box orientation check, or the Dimensional Weight Calculator to inspect one finished parcel.