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Shipping Box Size Calculator

Calculate dimensional (DIM) weight for FedEx, UPS, and USPS. Determine billable weight, box cubic volume, girth, and oversize packaging surcharges.

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What Is a Shipping Box Size Calculator?

The Shipping Box Size Calculator calculates the billable shipping weight, cubic volume, girth, and length-plus-girth of cardboard cartons and packages for major carriers including FedEx, UPS, and USPS based on dimensional weight (DIM weight) pricing rules.

How to Use This Calculator

Enter package length, width, and height in inches.
Enter the package’s actual scale weight in pounds.
Compare FedEx/UPS commercial DIM weight (divisor 139) vs USPS retail DIM weight (divisor 166).
Check if your carton exceeds the 130-inch Oversize threshold or 165-inch maximum carrier limits.

Dimensional Weight & Girth Equations

\text{DIM Wt}_{139} = \left\lceil\frac{L \times W \times H}{139}\right\rceil, \quad \text{Girth} = 2(W + H), \quad L + \text{Girth} = L + 2W + 2H

Carriers bill at the greater of actual scale weight or dimensional weight. Packages with Length + Girth > 130 inches incur substantial Large Package surcharges.

Worked Example

Scenario: Shipping a 20" × 14" × 12" carton weighing 15 lbs via FedEx Ground

Cubic volume: 20 × 14 × 12 = 3,360 cu in (1.94 cu ft).

DIM Weight: 3,360 / 139 = 24.17 → 25 lbs billable.

Actual scale weight: 15 lbs.

Girth: 2 × (14 + 12) = 52 inches; Length + Girth = 20 + 52 = 72 inches (Under 130" limit).

Result: Billable weight is 25 lbs (DIM weight applies instead of 15 lbs scale weight).

Tips & Key Notes

Always use the smallest box possible: trimming 2 inches from each dimension can save $10–$25 per package in DIM billing.
Measure the package at its thickest bulge, not just the flat carton edges, as carrier laser scanners measure peak dimensions.
Use corrugated cardboard with appropriate burst test ratings (e.g. 200 lb test / 32 ECT) for items over 20 lbs.

Frequently Asked Questions

What is dimensional weight (DIM weight)?

Dimensional weight is a pricing technique used by freight and parcel carriers that converts a package’s volume into an equivalent weight, ensuring light but bulky boxes pay their fair share of cargo truck space.

What DIM divisor do FedEx and UPS use?

Both FedEx and UPS use a divisor of 139 for all domestic and international shipments. USPS uses a divisor of 166 for Priority Mail packages exceeding 1 cubic foot.

How is package girth calculated?

Girth is the distance around the two smallest dimensions of the package: Girth = 2 × Width + 2 × Height. Total size is Length + Girth = Length + 2(Width + Height).

What happens if a box exceeds 130 inches Length + Girth?

Packages with Length + Girth exceeding 130 inches incur an Oversize or Large Package surcharge (typically $100 to $150+ per box). Packages exceeding 165 inches are refused for standard parcel delivery and must ship via LTL Freight.

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What Is a Shipping Box Size Calculator?

How to Use This Calculator

Enter package length, width, and height in inches.
Enter the package’s actual scale weight in pounds.
Compare FedEx/UPS commercial DIM weight (divisor 139) vs USPS retail DIM weight (divisor 166).
Check if your carton exceeds the 130-inch Oversize threshold or 165-inch maximum carrier limits.

Dimensional Weight & Girth Equations

\text{DIM Wt}_{139} = \left\lceil\frac{L \times W \times H}{139}\right\rceil, \quad \text{Girth} = 2(W + H), \quad L + \text{Girth} = L + 2W + 2H

Carriers bill at the greater of actual scale weight or dimensional weight. Packages with Length + Girth > 130 inches incur substantial Large Package surcharges.

Worked Example

Scenario: Shipping a 20" × 14" × 12" carton weighing 15 lbs via FedEx Ground

Cubic volume: 20 × 14 × 12 = 3,360 cu in (1.94 cu ft).

DIM Weight: 3,360 / 139 = 24.17 → 25 lbs billable.

Actual scale weight: 15 lbs.

Girth: 2 × (14 + 12) = 52 inches; Length + Girth = 20 + 52 = 72 inches (Under 130" limit).

Result: Billable weight is 25 lbs (DIM weight applies instead of 15 lbs scale weight).

Tips & Key Notes

Always use the smallest box possible: trimming 2 inches from each dimension can save $10–$25 per package in DIM billing.

Measure the package at its thickest bulge, not just the flat carton edges, as carrier laser scanners measure peak dimensions.

Use corrugated cardboard with appropriate burst test ratings (e.g. 200 lb test / 32 ECT) for items over 20 lbs.

Frequently Asked Questions

What is dimensional weight (DIM weight)?

What DIM divisor do FedEx and UPS use?

Both FedEx and UPS use a divisor of 139 for all domestic and international shipments. USPS uses a divisor of 166 for Priority Mail packages exceeding 1 cubic foot.

How is package girth calculated?

Girth is the distance around the two smallest dimensions of the package: Girth = 2 × Width + 2 × Height. Total size is Length + Girth = Length + 2(Width + Height).