SankalpROPP cap sizes are written as diameter by height in millimetres, for example 28mm by 18mm. The diameter is set by the bottle’s neck finish, and the height depends on the neck length and the seal you need. Always confirm the exact figures against a physical sample or drawing.
How to read a ROPP size (diameter by height)
An aluminium ROPP closure starts as a plain shell and is threaded onto the bottle during capping, so it does not carry pre-formed threads the way a moulded plastic cap does. Two numbers describe it:
- Diameter: the outer diameter of the shell in millimetres. This must match the bottle’s neck finish.
- Height (or skirt length): how far the cap skirt runs down the neck, again in millimetres.
So a size quoted as 28mm by 18mm means a 28mm diameter shell with an 18mm skirt height. Get the diameter right first. The height then follows the length of the threaded neck and the position of the pilfer band.
Standard ROPP cap size chart
The table below lists diameters that are widely used for aluminium ROPP closures, with typical height ranges and common Indian applications. Treat the heights as indicative ranges, not exact specifications. The correct height for any given bottle depends on its neck finish, so confirm before ordering.
| Diameter | Typical height range | Common application in India |
|---|---|---|
| 18mm | 15mm to 24mm | Pharma syrups, small tincture and essence bottles |
| 20mm | 15mm to 24mm | Pharma syrups, small edible-oil and flavouring bottles |
| 22mm | 18mm to 30mm | Liquor miniatures, syrups, speciality bottles |
| 25mm | 17mm to 30mm | Liquor and spirits, some pharma and food bottles |
| 28mm | 15mm to 24mm | Packaged drinking water, carbonated soft drinks, juices |
| 30mm | 18mm to 60mm | Liquor and spirits (including tall pilfer-proof skirts) |
| 31.5mm | 24mm to 60mm | Liquor and spirits, premium and export bottles |
| 38mm | 18mm to 33mm | Edible oils, wide-neck food and beverage bottles |
Heights vary widely within a single diameter because the same neck diameter can carry a short or a long skirt. Spirits bottles often use tall skirts for a fuller pilfer-proof band, while water and soft-drink bottles usually use shorter ones. Use the diameter to shortlist, then match the height to your actual bottle.
How to measure a bottle’s neck diameter and required cap height
You can get a close reading with a simple caliper and a clean, empty bottle:
- Measure the outer diameter of the neck at the point where the cap will seal, across the threads. This gives you the diameter figure to match.
- Measure from the top rim of the neck down to where you want the cap skirt to end. This gives you the approximate height.
- Note the neck finish type if it is stamped or documented, along with any drawing number from the bottle supplier.
A caliper reading gets you into the right size band, but it is a starting point, not a final specification. Threads, rim thickness, and glass or PET tolerances all affect fit, so verify with samples.
How the neck finish determines the size
The neck finish is the shaped, threaded top of the bottle: its diameter, thread profile, thread pitch, rim, and overall height. A ROPP shell is formed onto that finish during capping, so the finish, not the cap, drives the size. If the neck diameter is 28mm, you need a 28mm shell; a 30mm shell will not seal correctly on it.
Glass and PET bottles are made to defined neck-finish standards, and different bottle makers may use slightly different finishes at the same nominal diameter. So two 28mm bottles are not automatically interchangeable. Treat the neck finish as the single source of truth and match the closure to it, rather than assuming a nominal size guarantees a fit.
How to specify a size when ordering
When you request ROPP closures, give the supplier enough detail to match your exact neck finish:
- State the diameter and target height in millimetres, for example 28mm by 18mm.
- Name the segment and product so the seal and liner suit the contents (water, carbonated drink, spirit, or syrup).
- Share the bottle’s neck-finish drawing or standard reference if you have one.
- Send a physical bottle sample wherever possible. A sample removes ambiguity that a drawing alone can leave.
- For carbonated products, flag the pressure requirement so the closure and liner are rated for it.
Confirming against a sample or drawing before a full production run is the most reliable way to avoid leakers, poor thread pickup, or pilfer bands that sit at the wrong height. A short approval step up front is cheaper than reworking a filled batch.
Related guides
Frequently Asked Questions
How is a ROPP cap size measured?
A ROPP cap size is expressed as diameter by height in millimetres, such as 28mm by 18mm. The diameter is the outer diameter of the aluminium shell and must match the bottle’s neck finish. The height is the skirt length running down the neck. Diameter is fixed by the bottle; height depends on neck length and seal needs.
What are the most common ROPP cap diameters?
Widely used aluminium ROPP diameters include 18mm, 20mm, 22mm, 25mm, 28mm, 30mm, 31.5mm, and 38mm. Smaller diameters suit pharma syrups and miniatures, 28mm is common for water and soft drinks, and 30mm to 31.5mm are frequent on liquor and spirits. The right one is set by your bottle’s neck finish, so confirm against a sample.
Which ROPP cap size is used for packaged drinking water?
Packaged drinking water bottles in India commonly use a 28mm diameter ROPP closure with a tamper-evident band, though the exact height depends on the specific bottle’s neck finish. Because water bottle finishes vary between suppliers, verify the diameter and height against your actual bottle before ordering rather than assuming a nominal 28mm size will fit.
Are ROPP caps of the same diameter interchangeable between bottles?
Not always. Two bottles quoted at the same nominal diameter, such as 28mm, can still have slightly different neck finishes depending on the bottle maker. Thread profile, rim, and tolerances all affect fit. Treat the neck finish as the deciding factor and check a closure against your specific bottle before committing to a production quantity.
Do ROPP caps come with pre-formed threads?
No. A ROPP closure starts as a plain aluminium shell without threads. The threads and the pilfer-proof band are formed onto the shell during capping, when rollers press the metal against the bottle’s neck finish. This is why matching the shell diameter to the neck finish matters so much: the finish, not the cap, shapes the final thread.
How do I confirm the correct ROPP cap size for my bottle?
Measure the neck outer diameter and required skirt height with a caliper to shortlist a size, then verify with a physical sample or the bottle’s neck-finish drawing. Share the segment (water, soft drink, spirit, or syrup) and any pressure requirement with your supplier. Approving samples before a full run is the most reliable way to avoid fit issues.
R Vision Pvt. Ltd manufactures aluminium ROPP closures to your bottle’s neck-finish specification, from Nashik, Maharashtra.