If the ends of a stripe meet at the top of a tumbler but miss at the bottom, do not immediately widen the artwork. The sheet may be sitting crooked, the bottom of the print may reach onto a curve, or the pattern itself may not match. A plain-paper proof lets you tell those problems apart before you use a coated blank.

This test uses JoyClub's 20oz sublimation tumblers with a straight body and flat bottom. Measure a cup from the pack you intend to decorate. Capacity tells you how much it holds, not where a full-wrap graphic should start or stop.

Put a ruler mark on the proof

Cut a strip of plain paper long enough to circle the unheated cup. Set it on the straight portion, mark where its ends meet, then lay it flat and measure that distance. Measure the usable height separately, leaving out the lip and the lower curve. A flat base does not mean that the entire sidewall is straight.

Add a one-inch reference mark outside the artwork in your proof file. Print at actual size, then check the mark with a ruler. If it measures less than an inch, look for a fit-to-page setting before changing the design. Otherwise you may resize a perfectly good file to compensate for a printer setting.

Read the gap before changing the artwork

• A uniform gap: If the reference mark is correct, compare the proof width with your paper-strip measurement. A print cropped at one edge can look like a template that is too narrow.
• A wedge-shaped gap: Reseat the paper squarely on the straight wall. If the wedge remains, check whether the proof extends onto the lower curve. Widening the whole file may solve one end and spoil the other.
• Edges meet but the pattern jumps: Put the left and right edges of the design side by side on screen. A flower stem or stripe that changes height there will also jump on the finished cup.

Give the join a deliberate place

For a personalized gift, place the name opposite the join and turn the proof as though you were showing it to the recipient. Can you read the whole name in one view? For a repeating floral design, let a stretch of background meet at the join rather than cutting through a flower. This small change can save more work than adjusting the width again.

Where the paper ends meet is a measurement reference, not a universal overlap allowance. Use the transfer system's guidance for bleed and overlap. Remove the ruler mark from the final print file so it does not become part of the gift.

Separate fit problems from transfer problems

Use the blank and equipment instructions for one decorated sample. Once it has cooled safely, compare the join with the paper proof. If the proof aligns but the print has a faint second edge, check whether the transfer shifted before resizing the file. Keep the approved proof and a photo of the finished join with the artwork version.

Still comparing blank styles? The 20 oz tumbler buying guide covers the differences between the cup body, the base, and the accessories in a pack.