Most zippers that arrive at the wrong length were not made wrong. The buyer and the supplier measured different things: one measured the whole tape, the other only the chain, and both numbers were correct.
The fix is simple. Zipper length has a standard meaning, and once both sides use it, a length in an inquiry means the same thing to everyone.
What zipper length refers to
Zipper length is the length of the chain, the section with teeth, measured between the parts that end it. It does not include the extra tape beyond the teeth, and the slider is not an end point.
Two habits make the measurement reliable:
- Close the zipper fully before measuring.
- Lay it flat without stretching the tape.
If the part names are new to you, our guide to the parts of a zipper explains each one.
Measuring a closed-end zipper
A closed-end zipper has top stops at one end and a bottom stop at the other.
Measure from the top edge of the top stops to the bottom edge of the bottom stop. That is the length a closed-end zipper is ordered by, and the one a supplier will work from.
Measuring an open-end zipper
An open-end zipper has no bottom stop. Its lower end is the insertion pin and the box.
Measure from the top edge of the top stops to the bottom edge of the box. The box, not the tip of the pin, is the lower reference point. Our comparison of closed-end and open-end zippers covers where each structure is used.
Measuring a two-way zipper
A two-way zipper has a slider at each end, and how it ends depends on the structure:
- Two-way closed-end: there is a stop at each end. Measure from the outer edge of one to the outer edge of the other.
- Two-way open-end: there is no fixed box at the bottom, because the lower slider does that job. The usual reference is the bottom of the reinforced section at the base of the chain.
Conventions for two-way zippers vary more than for the other structures, so it is worth saying which end points you used when you send the length.
Tape ends are not part of the length
Most zippers have some extra tape above the top stops, and often below the bottom end as well. That tape is there to be sewn into a seam or trimmed, and it is never part of the stated length.
When you measure an existing zipper, start at the first metal or plastic part, not at the edge of the fabric. When you receive zippers, expect the tape to extend past the length you ordered.
Working back from the garment or bag
If you are choosing a length rather than copying one, start from the finished opening, not from the pattern piece. The pattern includes seam allowances; the opening is where the chain will actually sit.
How the chain relates to the opening depends on the construction. A zipper that runs into a collar, a waistband, or a bag gusset is set differently from one that stops short of the edge. When the construction is new, a sample is the quickest way to confirm the length before bulk production, and sampling for standard specifications usually takes about 3 days.
How to state length in an inquiry
A length on its own is easy to misread. A complete line includes:
- the length and the unit, for example 60 cm
- the structure: closed-end, open-end, or two-way
- how it was measured: from the top stop to the bottom stop, or to the bottom of the box
Written that way, "60 cm open-end, measured from the top stop to the bottom of the box" leaves nothing to interpret. If you have a reference zipper, a photo with a ruler beside it helps as much as the number. Our guide to preparing a zipper inquiry lists the other details worth sending.
Conclusion
Zipper length is the chain between its end parts, measured closed and flat: top stop to bottom stop on a closed-end zipper, top stop to the bottom of the box on an open-end one. The tape beyond those points is extra.
When you are ready, send your lengths through our quote page and say how you measured them. We will confirm each one against the structure before sampling.