Measure the widest points
Include shoulders, caps, pumps, labels and other protrusions. For a round vessel, record its maximum diameter and total height. For an irregular shape, share photographs or a physical sample alongside the measurements.
Label the units
Use one unit consistently and state it clearly. Millimeters are useful for detailed packaging work. Do not mix product measurements and proposed internal box dimensions.
Allow the fit to be developed
Product dimensions are a starting point, not a finished dieline. Board thickness, insert construction and packing clearance affect the final internal dimensions.
Check with the real item
A digital drawing cannot confirm every aspect of fit. Verify the sample with the actual product and review how easily it can be packed and removed.