Zipper Size Chart — Measure Zipper Size in mm

Size a Zipper You Are Holding

Calibrate once, close the zipper, and lay the teeth along a slot. The slot whose edges meet the edges of the teeth is the size. Measured it already? Type the width in millimetres.

Calibration 96 PPI

Lay a bank card on the outline and drag until the widths match. Every card is 85.6 mm wide.

Closed-teeth width, actual size

Or type the measured width (mm)

What a Zipper Size Number Means

The number on a zipper, #3, #5, #8, is its gauge, and it is, to a first approximation, the width in millimetres of the closed teeth. Not the tape the teeth are sewn to, and not the length: just the chain, measured across, once the zipper is shut. A #5 has a chain about 5 mm wide. A #10 is about twice that.

It is a trade label rather than an ISO dimension, so the real width runs slightly either side of the number and differs a little between coil, moulded plastic and metal. Treat the table below as the nominal size each label implies, not a tolerance.

Zipper Size Chart in mm

Size	Teeth width (nominal)	Character	Typical uses
#3	3 mm	Fine and lightweight	Skirts, dresses, pillow covers, pockets
#4.5	4.5 mm	Mid-light	Trousers, light jackets, cushions
#5	5 mm	The general-purpose size	Jeans, jackets, bags, hoodies
#8	7.5 mm	Heavy duty	Heavy coats, sleeping bags, tents, holdalls
#10	9.5 mm	Heaviest common size	Parkas, luggage, tarps, upholstery

These are the commonly stocked sizes. Others exist, such as #2 below the range and #6, #7 and #9 between the entries, but they are rarer and are not given a row here. The uses are conventions, not specifications: makers vary, and a heavier chain than the garment needs is often a deliberate design choice.

How to Measure a Zipper Size

Close the zipper so the teeth are interlocked, because an open pair of rows measures wrong. Then measure across the teeth from one outer edge to the other at the widest point of the chain, and ignore the tape. For metal and moulded plastic that is the chain you can see. For a coil zipper it is the width of the visible coil.

If the slider is still on, look at the back of it first. The number is usually stamped there, beside the maker's logo. Measuring is for when the stamp has worn off, the slider is gone, or you are matching tape without a slider at all.

The mismatch that matters

A slider is made for one chain width. One a size too big lets the teeth pop apart behind it, and one a size too small jams or splits the chain. Neighbouring sizes look nearly identical held in the hand, which is exactly why this is worth measuring rather than guessing.

Why a Printed Zipper Size Chart Can Mislead

The standard advice is to print a to-scale chart and lay the zipper on it. That works only if the sheet came out at exactly 100%, and almost nothing prints at exactly 100% by default. Browsers apply "fit to page" or shrink-to-margins scaling, and nothing on the printed page shows that it happened. These sizes are only a millimetre or two apart, so a few percent of shrinkage reads a size low.

Calibrating a screen has the same requirement, but it is done once, visibly, against a thing of known width, and it is obvious when it is wrong. The calibration is shared with the online ruler, the button size chart and the fabric count gauge, so calibrating on one calibrates the rest on that screen.

How much to trust it

The common sizes sit 1.5 to 2.5 mm apart, and a careful bank-card calibration is well inside that, so the answer is usually decisive. The failure mode is browser zoom: calibrate at 100%, and recalibrate if you change it, because zoom rescales the slots and the card outline together and the outline will still look correct. If the teeth land between two slots, type the width in millimetres and settle it against the stamp.

Frequently Asked Questions

How do I measure zipper size in mm?

Close the zipper and measure across the teeth, edge to edge, at the widest point of the closed chain. Do not include the tape. That width in millimetres is, to a first approximation, the zipper's number: about 5 mm is a #5, about 3 mm a #3. If you have no calipers, lay the closed teeth against the calibrated slots above and find the one whose edges sit on the teeth's edges.

What does the zipper size number mean?

It is the gauge, and it roughly equals the width of the closed teeth in millimetres. A #3 has a chain about 3 mm wide, a #5 about 5 mm, a #10 about 9-10 mm. It is a trade label rather than an ISO dimension, so real chains vary slightly either side and by construction.

What size is a #3 zipper, and how wide is a #5 zipper in mm?

A #3 zipper has closed teeth about 3 mm wide, and a #5 zipper size in mm is about 5. Those are nominal figures: the number is a trade label for the chain width, so a real #5 can read a fraction either side of 5 mm.

Where is the size stamped on a zipper?

Usually on the back of the slider, next to or under the manufacturer's logo, with a number such as 3, 5, 8 or 10. It wears off on old or heavily used zippers, which is the situation where measuring the teeth is the way to find it.

What is the difference between a #3, #5 and #8 zipper?

Width and duty. A #3 is fine and light, used on skirts, dresses and cushion covers. A #5 is the general-purpose size on jeans, jackets and bags. A #8 is a heavy-duty chain for coats, tents and sleeping bags. A bigger number is a wider, stronger chain, and a slider only fits the size it was made for.

Can I use a #5 slider on a #4.5 zipper?

Do not count on it. A slider is made for one chain width, and a slider that is even slightly too large lets the teeth separate, while one too small jams. The sizes sit close together on purpose, so match the slider to the measured chain, and check it against the stamp on the old slider if you still have it.

Are metal, plastic and coil zippers measured the same way?

The number means the same thing, the width of the closed teeth, but the chains look different, so measure the closed chain itself in each case. Metal teeth are measured across the metal and moulded plastic across the moulded teeth. Coil zippers are measured across the visible coil, not the tape beside it.

Why does a printed zipper size chart give wrong results?

Because printers rarely print at exactly 100%. Fit to page and shrink-to-margin scaling quietly rescale every dimension, so a printed template reads a few percent small. A zipper sizes only a millimetre or two apart, so that is enough to push it a size down. The printed chart is only trustworthy if you check it against a ruler first.

How accurate is measuring a zipper against a screen?

Accurate enough to choose between neighbouring sizes if you calibrate carefully, which is not true of every use of this technique. The gaps between the common sizes are 1.5 to 2.5 mm, comfortably above a careful bank-card calibration error. The failure mode is browser zoom: calibrate at 100% and recalibrate if you change it.

What can I use to calibrate the gauge?

Any bank, credit or ID card. They are all 85.6 mm wide by the ISO/IEC 7810 ID-1 standard, which is why the outline above is that size. Drag the slider until the outline matches a real card laid on the screen.

Does the zipper tape width matter?

Not for the size number. Tape width affects how it is sewn in, but the gauge, and so the slider you need, is set only by the closed teeth. Tape colour and length matter for a replacement but are separate from size.