How to Read a Glass Bottle Specification Sheet

Two bottles can look identical in a photo and be completely incompatible with your closure. The difference is in the numbers. This guide explains every line on a glass packaging spec sheet — so you can place an order that fits the first time.

The anatomy of a spec sheet

A proper specification has two parts: a drawing (dimensions with tolerances) and a parameter table (the numbers). Both matter. The drawing tells you if it fits your label and shelf; the table tells you if it fits your cap and filling line.

Core parameters, line by line

Decoding neck finishes — the part people get wrong

A neck finish is written as two numbers, like 18/415:

• First number (18) — the outer diameter of the opening in millimetres
• Second number (415) — a code for the thread style and height (the "GPI finish")

Common finishes and what they are used for:

Critical rule: the bottle finish and the closure finish must match exactly. An 18/415 cap will not seal an 18/410 bottle, even though both are "18". This mismatch is the most common cause of a failed first order.

Capacity versus brimful — why 30 ml is not 30 ml

A "30 ml bottle" holds about 30 ml of product, but its physical volume to the brim is larger — typically 33–36 ml. That headroom exists because:

• Closures displace volume when inserted
• Liquids expand with temperature
• Filling lines need a safety margin to avoid overflow

If you are designing a label or calculating freight, use the brimful figure. If you are selling to consumers, use the nominal capacity.

Tolerances: why ±1 mm changes everything

Glass is formed at high temperature, so dimensions vary slightly. Standard tolerances are roughly:

• Height: ±1.0 mm
• Diameter: ±1.0 mm (often ±1.5 mm on larger bottles)
• Weight: ±5%
• Capacity: ±3% typical

These matter when you have automated filling or tight label tolerances. If your equipment is sensitive, say so up front — tighter tolerances are possible but affect price and yield.

What to send a supplier (and what to demand back)

Send this

• Capacity, preferred shape and closure type
• Neck finish if you already have a closure (or the closure you plan to buy)
• Product type — oil, alcohol-based, acidic, carbonated
• Quantity and decoration requirements
• Any filling-line constraints

Demand this back

• A dimensioned drawing, not just a photo
• The full parameter table including brimful capacity and weight
• Neck finish stated explicitly in the GPI format
• Stated tolerances
• Material and compliance statement (FDA / EU food contact as applicable)
• A physical sample for fit testing before production

Quick reference: reading a drawing

1. H — overall height (body + neck)
2. D — body diameter (widest point)
3. d — neck / bore diameter
4. T — thread height on screw finishes
5. S — the "T" dimension on a crimp finish (the crimp ring diameter)

If a drawing is missing any of these, ask. A supplier who cannot produce a proper drawing is probably not the supplier for a production order.