Every Bottle Has Two Volumes
Fill a bottle labelled "500 ml" to the brim with water, measure it, and you will get more than 500. That is not an error; every bottle has two separate volumes, and each serves a different purpose.
Nominal volume is the volume the bottle is sold as and that is declared on the label: 50 ml, 100 ml, 500 ml. Brimful capacity is the amount of liquid the bottle holds when filled right up to the overflow point. The difference between them is the headspace: the gap left above the liquid.
Technical drawings and spec sheets usually state the brimful capacity, because that is the value that can be measured and given a tolerance. Product names, on the other hand, use the nominal volume. Confusing the two comes back to you as overflowing bottles on the filling line, or products that look half full.
Why Leave Headspace?
Headspace is not waste; it answers three separate needs.
Thermal expansion. Liquids expand as they warm, and ethanol expands noticeably more than water. A perfume filled in winter gains volume in a hot car or warehouse in summer. Without headspace, the pressure forces the valve, the gasket or the plug, and leakage begins.
The valve and dip tube. In a pump bottle, the valve body and tube take up space inside the bottle. When the closure is fitted, the liquid rises by that volume. Fitting a valve to a bottle filled to the brim means spilling.
Filling tolerance. No filling system delivers exactly the same amount into every bottle, and the internal volume of the bottles themselves varies within the production tolerance. Headspace absorbs both deviations.
Examples with Real Bottles
The values below are taken from the technical drawings of products on esans.com.tr. Note the difference between the brimful capacity and the volume in the product's name.
| Bottle | Volume in the name | Brimful capacity | Difference | Difference relative to the named volume |
|---|---|---|---|---|
| Glass perfume bottle (Core) | 100 ml | 105 ml | 5 ml | 5% |
| Glass perfume bottle (And) | 100 ml | 111 ml | 11 ml | 11% |
| Aluminium bottle (T36255) | 250 ml | 295 ml | 45 ml | 18% |
| Aluminium bottle (T36256) | 500 ml | 620 ml | 120 ml | 24% |
The table tells us two things. First, two bottles with the same nominal volume can have different brimful capacities; there is a 6 ml difference between two 100 ml glass bottles. Second, storage and shipping bottles have a wider margin: the product inside is usually sold by weight and takes up a different volume depending on its density.
500 grams of a fragrance oil with a density of 0.95 g/ml comes to about 526 ml. A bottle that is nominally 500 ml but holds 620 ml brimful carries those 526 ml with comfortable headspace. If the bottle held exactly 500 ml, half a kilo of the same oil would not fit.
How to Calculate the Fill Quantity
Work out the target fill for your own product in this order.
- Find the brimful capacity
Take it from the spec sheet or technical drawing. If there is no document, weigh the bottle, fill it to the brim with water and weigh it again; the difference in grams gives the approximate millilitres.
- Subtract the volume taken up by the valve
You can find it by measuring the water displaced from a full bottle with and without the valve fitted. For small perfume valves this is a few millilitres.
- Set aside expansion headspace
For alcohol-based products, leaving at least 3 to 5 percent of the remaining volume empty is a common starting point. If your product is going to a hot climate, increase the margin.
- Compare with the declared volume
The remaining volume must not be smaller than the volume you will declare on the label. If it is, either choose a larger bottle or lower the declaration; underfilling is a legal problem.
- Verify by weight
Check the fill on a scale: target grams = target ml × the product's density. In an alcohol-based perfume the density is below 1; 100 ml of product weighs less than 100 grams.
Frequently Asked Questions
Questions about volume come up most often in the first production run, when the bottles arrive at the filling table.
What is the difference between nominal volume and brimful capacity?
Can I fill exactly 100 ml into a 100 ml bottle?
Why does my bottle look underfilled?
How much headspace should there be?
What does brimful capacity mean?
Which volume should I put on the label?
How do I check volume by weight?
Why do two bottles of the same volume have different brimful capacities?
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