NOTES FROM THE WORKBENCH
Paper weight is not paper thickness
The number on a paper pack usually describes mass per area. The box model needs a different property when it asks for thickness.
Reviewed October 27, 2026
Read the units on the label
GSM means grams per square metre. It tells you how much a sheet of a given area weighs. Caliper or thickness tells you how far apart the two sheet surfaces are. These properties can be related for a particular stock, but they are not interchangeable.
Two papers with the same GSM can differ in fibre composition, coating and bulk. There is no universal conversion factor that turns every 250 gsm paper into one accurate millimetre thickness.
Find a value for the actual stock
Look for a caliper specification in the manufacturer's data for the exact product, or measure the stock with an appropriate instrument and method. Record the units. If you measure a stack, avoid treating an uneven or heavily compressed stack as a precise single-sheet reading.
The 0.30 mm used in FoldParcel's examples is an illustrative thickness input. It is not the default thickness of all cardstock and should not be substituted simply because the pack has a familiar weight.
Understand what the model changes
The simplified tuck-box model adds one thickness to each approximate inside target to estimate fold-line spans. The two-piece model also estimates the outside of the base before adding lid clearance. A wrong thickness can therefore change several related measurements.
That does not mean an accurate caliper guarantees a perfect finished fit. Scoring, bending, glue and fabrication variation still affect the object.
Keep stock information with the project
Name the paper product and record the thickness source with your project notes. When trying a different paper, duplicate the project instead of silently overwriting the working settings.
Make a fresh trial in the new stock and check print scale first. This keeps a material comparison separate from a printer-scaling problem and gives you a useful record for the next version.
Sources and methods
Ready to make something?
Set the dimensions. Check the folds. Make a small test box.