Three numbers on a bottle drawing decide whether your product can be filled at all. Fill volume is how much goes in. Headspace is the air left above it. Tare weight is the empty bottle before anything goes in. Send a bottle without these three and the filler cannot quote the run, size the pump or set the checkweigher target.
Quick answer
- Headspace is not spare room; it absorbs thermal expansion, foam collapse and pump vacuum, and removing it causes container failure.
- Tare weight has to be known before filling because gravimetric fillers weigh the container to set the dose.
- Brimful capacity, nominal fill, neck finish and bottle weight belong on the same drawing as the filling note.
What do fill volume, headspace and tare weight mean?
These three terms come from the filling line, not from the design studio, and they are often used as if they were interchangeable. They describe three different physical facts about the same container.
| Term | What it measures | Who needs it | What goes wrong without it |
|---|---|---|---|
| Fill volume | The volume of product the filled pack is required to contain, at the nominal target | Filler, QA, the label claim | Under-filling breaks a volume claim; over-filling raises spill, weight and closure torque problems |
| Headspace | The volume between the product surface and the underside of the closure, expressed as volume or as a percentage of brimful capacity | Formulator, filler, closure supplier | Expansion pressure, foam collapse void or pump vacuum can split the pack or make it impossible to seal |
| Tare weight | The weight of the empty, decorated bottle plus its closure and liner, before product | Filler, checkweigher, materials buyer | A gravimetric filler cannot dose; a checkweigher rejects every unit |
Two related numbers usually travel with them. Brimful capacity is the volume up to the top of the neck with no closure fitted — the physical maximum the bottle can hold. Nominal capacity is the commercial size, such as 30 ml or 250 ml, which is what appears on the label. Brimful capacity is always larger than nominal capacity, and the difference is usually headspace plus the space the closure displaces. Our guide on bottle capacity and fill volume covers how to choose between them, and the five numbers on a spec sheet shows where each belongs.
Why does the filler need the tare weight before filling?
Because the most accurate filling machines do not measure volume, they measure weight. A gravimetric filler works out the net content by weighing the container before and after the dose, then dosing until the difference equals the target.
| Filling mode | How it doses | What the machine needs from the bottle | Typical tolerance effect |
|---|---|---|---|
| Volumetric piston | Mechanical stroke delivers a fixed volume | Consistent brimful volume and a stable internal diameter; product viscosity handled by stroke and speed | Drifts with product viscosity and temperature |
| Gravimetric | Weighs the empty container, then doses by weight difference | Accurate tare weight for that exact bottle, decoration and closure | Tightest weight control, and totally dependent on tare accuracy |
| Volumetric with density correction | Fixed stroke corrected by measured density and fill level | Brimful capacity, headspace and a level-detection position | Good on thin liquids, weaker on foaming products |
| Piston with level probe | Stroke sets volume, probe confirms the level | A clean, conductive or optical target area inside the neck | Detects short fill, but cannot fix a wrong target |
Two practical consequences. First, if you add a decoration method, tare weight changes: silk screen ink, a label or a liner each add weight, and the filler’s recipe has to be set for the decorated pack, not the bare bottle. Second, bottle weight tolerance matters directly to fill accuracy, because a bottle that arrives lighter than quoted shifts every gravimetric dose on that production lot. That is why the weight tolerance article matters to the filling line and not only to your invoice.
How much headspace does a product actually need?
Headspace is a working volume with four jobs. Sizing it at zero because the bottle looks full is one of the most expensive errors in cosmetic packaging, and it usually shows up as a line-stop rather than as a complaint.
| What needs the headspace | What happens if there is not enough | Typical fix |
|---|---|---|
| Thermal expansion of the product | Pressure builds under a sealed closure; the pack distorts, leaks or splits at the seal | Keep fill below brimful capacity by a defined amount and confirm with a heat test |
| Foam and entrained air | Foam collapses over days, leaving a visible void and a lowered net fill | Allow extra headspace for foaming formulas and define a settling time |
| Pump vacuum for spray and lotion systems | The pump draws harder, loses prime, or pulls product back through the neck | Specify a headspace range with the pump supplier rather than a single fill point |
| Thermal headspace for reversible packs and air-filled cushioning | Air-filled structures cannot be sealed without a defined volume above the fill | Headspace is a designed value on the drawing, not a tolerance gap |
The normal way this is handled is a range, not a number. Ask for a target fill with an acceptable band, state it as volume and as a percentage of brimful capacity, and confirm the band against your formula’s expansion behaviour and your closure’s torque window. For toners, essences and thin mists the band is typically narrow because spray performance is sensitive to the fill level; for heavier creams the band is wider but the torque and expansion limits are tighter. Our guide to PET toner bottles and filling tips covers how neck finish and fill level interact on spray formats.
What does a bottle need to survive a filling line?
A bottle that is excellent on a shelf can be un-fillable on a line. The line cares about geometry and repeatability, not appearance. These are the features a filler is actually testing for.
| Line feature | What the bottle must provide | Failure seen in production |
|---|---|---|
| Machine gripper | A stable, straight body section that a star wheel or gripper can hold without slipping or crushing | Bottle spins at the star wheel, jams, or is crushed by an over-gripped neck |
| Infeed conveyor | Consistent base geometry so the bottle stands upright through the sorter | Bottle tips over at the infeed and the line stops |
| Label or sleeve station | A defined, flat label panel, and a defined panel start position relative to the front of the bottle | Label skew, twisted wrap, or a bottle that rotates freely after capping |
| Capping and torque | A neck finish that matches the closure, with adequate thread engagement and a defined seal land | Closure stops short, cross-threads, or reaches torque before sealing |
| Spray pump assembly | Enough neck length and thread depth for the pump ferrule, and a flat shoulder or seating face | Pump sits proud, leaks at the neck, or cannot be crimped |
| Level detection | A usable target surface inside the neck for capacitive, optical or ultrasonic probes | Filler cannot confirm fill level and runs open-loop |
| Sealing | A closure land that accepts induction or heat-seal film without distorting the neck | Poor seal, leak on the shelf, and product lost in transit |
The item buyers most often forget is label-panel position. On a decorated bottle, the panel has to be defined relative to the front, otherwise the artwork rotates between the filler and the labeller and no two bottles on the shelf face the same way. It also decides where a code can be printed so the coder does not print onto a seam or a curved shoulder.
What should be annotated on the drawing before the bottle is made?
Ten annotations turn a bottle from a shape into a fillable container. Send them with the drawing, not in an email after the tool is cut.
- Nominal fill volume and the acceptable tolerance band
- Brimful capacity, measured or calculated
- Headspace target, expressed in volume and as a percentage of brimful capacity
- Empty bottle weight and the acceptable weight tolerance
- Neck finish in millimetres and thread pitch
- Closure part number, liner material and target torque range
- Machine gripper zone and infeed base requirement
- Label panel dimensions and its position relative to the bottle front
- Pump assembly requirements, including ferrule seat and assembly depth
- Level-detection target position inside the neck
- Decoration version, including where any code or print area sits
- Sealing method: induction, hot melt, or a screw closure only
Headspace, empty weight and decoration version are the three that come back to bite. They are decided at the filling line if they are not on the drawing, and by then the mould is already paid for — and a new tool adds roughly 30 working days.
Why does the factory still ask about filling after you send the formula?
Because the formula answers a chemical question and the factory answers a packaging one. The formula tells you what goes in; it does not tell you what the container has to survive. We need the filling method before we recommend a bottle, and the reason is always one of these four.
| What the formula tells us | What we still need to know | Why the container changes |
|---|---|---|
| Viscosity at filling temperature | Filling mode: volumetric, gravimetric, or piston with level probe | High viscosity needs bigger bores and slower speeds, which changes the neck and the pump |
| Whether the formula foams | Defoaming or vacuum capability on the line, and a settling allowance | Foaming needs extra headspace and a taller neck than the nominal fill would suggest |
| Solvent and active content | Permeation expectation and closure seal requirement | A volatile or aggressive formula may rule out a resin grade or require a barrier closure and liner |
| Nominal quantity per pack | Fill accuracy target and whether the line runs gravimetric or volumetric | Accuracy expectations change the neck design, the checkweigher setup and the closure |
So the questions are not redundant. “What is your formula” answers what is in the pack. “How do you fill it, at what speed, on what machine, with what closure torque and what accuracy target” answers what the bottle has to be. The second set is the one that determines whether your first production run is smooth. Compatibility of the formula against the resin is a separate question we handle separately, because a chemically unsuitable bottle fails on the shelf rather than on the line.
What are the three filling-line mistakes we see most often?
1. Treating fill volume as brimful capacity. Filling a bottle to the top of the neck leaves no headspace, and the first hot warehouse or a hot delivery truck creates the pressure that cracks or leaks the pack. Specify the fill as a target below brimful capacity and hold the difference as a designed headspace value.
2. Quoting an empty bottle weight without decoration or closure. A tare weight for a bare bottle is not a tare weight for the pack that gets filled. Add the label, the silk screen ink, the closure and the liner before the filling recipe is set, otherwise every unit is dosed to a target that does not match the pack on the line.
3. Designing the neck and pump separately. A bottle that looks correct in a rendering can leave a pump ferrule without enough thread engagement to reach torque, or a neck with no level-detection surface, and both are discovered at the customer’s line rather than in the sample room. Send the pump part number to the bottle drawing stage, not after the first sample arrives.
Frequently asked questions
Is headspace included in nominal capacity?
No. Nominal capacity is the labelled fill amount. Headspace is the additional volume between the product and the closure, and it is part of brimful capacity together with the space the closure displaces.
Does a thicker bottle wall change headspace?
It changes brimful capacity for the same external volume. Two bottles of the same nominal fill can have different headspace because their internal volumes differ, which is why headspace must be specified against brimful capacity, not against nominal fill.
Why does a spray product care more about headspace than a cream?
A spray pump draws air from the headspace to prime and to drive the dose. Too little headspace means hard priming, lost spray performance or product drawn back through the neck. The usable range is set with the pump supplier.
Do I need tare weight if the filler is volumetric?
It is still needed. Net weight is used for shipping data, for the checkweigher and for duty and label declarations. Volumetric filling reduces the dependence on tare weight, it does not remove it.
Can the bottle maker change the fill volume after the mould is cut?
The mould cannot be changed, but the fill level is a filling-line setting, not a bottle feature. What the mould fixes is the brimful capacity and the neck. Choose a capacity range that covers your planned fill targets so the bottle is not limited later.
What accuracy can I expect on a filled cosmetic pack?
Accuracy depends on the filling mode. A gravimetric filler holds the tightest weight control, a piston filler drifts with viscosity and temperature. State the tolerance you need as a band and let the filling method be chosen around it.
About Shijin Packaging
Shijin Packaging Products Co., Ltd. has been manufacturing plastic packaging in Shenzhen, Huizhou and Guangzhou since 2003. We hold more than 2,000 existing moulds, run ISO 9001, GRS and SGS audited production, and ship roughly 500,000 bottles a day for cosmetic, personal care, household, car care and food-grade customers. New tooling takes roughly 30 working days, and every drawing we release carries the fill, headspace, brimful capacity and empty weight annotations a filler needs.
Send us the fill brief: tell us your nominal fill, your formula type and viscosity, your closure or pump part number and your accuracy target, and we will return a bottle and closure combination with the headspace, gripper zone and label panel defined on the drawing.