How to measure a packaging box

How to Measure a Box

Accurate dimensions reduce cost, prevent fit issues, and keep shipping charges predictable. Use this guide to capture the **correct internal dimensions**—and let Influence Packaging optimize your carton and insert design.

Measure Internally Order: L × W × H Specify Units (in/mm)

The Three Box Dimensions (Internal)

DimensionWhat it meansHow to measure
Length (L) Longest side of the box opening. Measure inside edge-to-edge along the longer open side.
Width (W) Shorter side of the box opening. Measure inside edge-to-edge across the shorter open side.
Height (H) Depth from the opening down to the base. Measure inside from the top opening to the bottom panel.

Always state dimensions in the order L × W × H. Internal dimensions ensure your product and inserts fit as intended.

Step-by-Step: Measure Like a Pro

  1. Prepare the box: Set it upright with flaps open and facing up.
  2. Measure Length: Inside, along the longest open side.
  3. Measure Width: Inside, across the shorter open side.
  4. Measure Height: Inside, from the opening down to the base.
  5. Record units: Use inches (in) or millimeters (mm) consistently.
  6. Note tolerances: Corrugated production typically varies ±1/8″ (±3 mm).

Internal vs. External Dimensions

  • Internal: For product fit, inserts, and protective packaging.
  • External: For palletization, storage clearances, and carrier calculations.

We engineer both—fit on the inside, efficiency on the outside.

Cost & Shipping Tips

  • Dimensional Weight (DIM): Carriers often bill by (L × W × H) ÷ divisor (e.g., 139). Reducing 1–2″ can materially cut costs.
  • Insert Optimization: Right-sized inserts stabilize products and allow smaller cartons.
  • Material Choice: Use appropriate board grade—strong enough, not overbuilt.