"50 ml" on a jar is a nominal size, not the volume you fill. The drawing specifies brim-full capacity ±5% (measured with 20°C water) and a fill line with headspace below it; a 50 ml thick-wall glass jar is typically brim-full at 60–65 ml and filled to about 50, while a lined acrylic jar holds noticeably less than its outer size suggests because the PP cup, not the shell, holds the cream. Specify both figures on the drawing, state the fill in grams at your cream's density, and never fill a lined acrylic jar to the brim — bulk creeping between cup and shell causes crazing.
Three capacities, one word
Every jar has three volumes and most briefs mention only one.
- Nominal capacity is the catalogue size: 15, 30, 50, 100 ml. It names the jar family and roughly matches the intended fill. It is not a measurement.
- Brim-full capacity is the physical volume of the cavity to the rim, measured by filling with water at 20°C and weighing. It is the only capacity a factory can hold to a tolerance, and the standard tolerance is ±5%.
- Fill capacity is what your filler puts in, set by a fill line below the brim. The gap between fill line and brim is headspace: room for the inner lid or disc liner to seat, for the cream to expand in a 48°C container, for the spatula, and for the surface not to smear the lid on opening.
A jar is sold by its nominal size, made to its brim-full size and used at its fill size. When a quote, a drawing and a filling order each use a different one of the three, the jar "holds less than 50 ml" — or, more often, the cream arrives 20% short of the rim and looks under-filled on shelf.
The numbers on a thick-wall glass jar
Thick-wall glass shows the gap most clearly because the wall itself is 3–7 mm and the brim sits well above the fill line. Typical partner-factory ranges for a straight-sided wide-mouth jar:
| Nominal size | Typical wide-mouth neck | Wall and weight | Brim-full ≈ | Headspace at nominal fill |
|---|---|---|---|---|
| 30 ml | Ø43 or Ø48 mm | ~3–5 mm; ~90–140 g | ≈40 ml | ≈10 ml, about 25% of brim volume |
| 50 ml | Ø48 or Ø53 mm | ~3–5 mm; ~150–220 g | ≈60–65 ml | ≈10–15 ml, about 17–23% |
| 100 ml | Ø53 or Ø63 mm | ~3–5 mm; ~220–320 g | ≈115–125 ml | ≈15–25 ml |
| 150 ml | Ø63 or Ø70 mm | ~4–6 mm; ~300–420 g | ≈170–185 ml | ≈20–35 ml |
| 200–250 ml | Ø70 or Ø83 mm | ~4–6 mm; ~380–550 g | ≈230–290 ml | ≈30–40 ml |
| 400–500 ml | Ø83, Ø89 or Ø100 mm | ~5–7 mm; ~600–900 g | ≈460–580 ml | ≈60–80 ml |
Read the 50 ml row as a specification, not a curiosity: the factory guarantees a cavity of roughly 60–65 ml ±5%, and where you draw the fill line inside that cavity is your decision, written on the drawing. If the line is not on the drawing, the filler will pick one, and the first production batch decides your shelf look by accident.
Why a lined acrylic jar holds even less
An acrylic (PMMA) jar is an outer shell; a PP inner cup holds the cream, because oils and alcohol craze and cloud PMMA. The cup has its own wall, sits inside the shell's wall, and stops short of the shell's rim so that the inner lid can seat on the cup. So the usable volume is the cup's brim-full volume minus headspace — two steps down from the outer size that the shelf sees. A double-wall acrylic jar that measures like a 60 ml object may carry a 50 ml nominal cup filled to 45–50 g. That is not a defect; it is how the format works, and the heavy, thick-wall look is exactly what the brand is paying for.
The rule that follows is absolute: do not fill a lined acrylic jar to the brim. Cream that creeps over the cup rim into the gap between cup and shell attacks the acrylic from the inside, and the damage shows weeks later as crazing or a milky bloom in the double wall. The compatibility test for an acrylic jar — the actual cream in the PP cup at 48°C for 30 days — includes "no crazing of the acrylic shell" as a pass criterion for exactly this reason. See acrylic vs glass vs PP for the material decision.
Grams, millilitres and density
Fillers work in grams; jars are specified in millilitres. A water-thin gel at a density near 1.0 puts 50 g into about 50 ml; a whipped or oil-rich cream lighter than water takes more than 50 ml for the same 50 g; a dense clay mask heavier than water takes less. State the fill in grams at your cream's density and let the fill line follow, or state the fill line in millilitres and accept that the declared net weight follows the density. Doing neither is how a 50 ml jar ends up over-filled with a light whipped cream.
What the drawing and the QC sheet should say
| Item | Specification | How it is checked |
|---|---|---|
| Nominal capacity | The catalogue size (e.g. 50 ml) | Naming only; not measured |
| Brim-full capacity | Stated in ml with ±5% tolerance | Filled with 20°C water and weighed; on the QC sheet as "weight ±10%; brim-full capacity ±5%" |
| Fill line / fill volume | Stated in ml, or in g at a stated density | Marked on the drawing; checked on the filling line, not by the jar factory |
| Headspace | Brim minus fill; large enough for inner lid, foil seal, spatula and 48°C expansion | Inner lid seats without contacting the cream surface |
| Lined acrylic | Cup brim-full and cup fill line, both below the shell rim | 48°C / 30-day test: no crazing of the shell |
| Dimensions | Fit-critical ≤0.5 mm; height and width ≤1.0 mm; lid-to-jar thread clearance 0.1–0.8 mm | Calliper at IQC and FQC |
| Seal with the chosen headspace | Jar 3/4 filled with dyed water, lid fitted, lying and inverted | −0.06 MPa for 5 min, no dye outside the seal area; 24 h inverted, no leak |
Two practical consequences. First, if you are comparing quotes, compare brim-full figures, because two "50 ml" jars from two factories may be 55 and 65 ml cavities and will look completely different when filled to the same 50 g. Second, re-measure brim-full whenever a stock jar is reordered from a second mould before the fill line is copied across. The wide-mouth finishes that go with each size (Ø33–Ø100) and the liner and torque rules are on neck finish and closure standards; the glass forming methods and defect limits are on glass bottle specifications.
The "capacity short on the filling line" failure
It appears in the failure-mode list for glass jars for a reason. The root cause is almost always brim-full quoted as fill capacity: the buyer asked for 50 ml, the factory confirmed a 50 ml brim-full cavity (a smaller jar than the founder pictured), and the filler cannot get 50 g in with room for the lid. The check that catches it is at the specification stage, weeks before any glass is made — both figures on the drawing and a filled, lidded golden sample signed before production. The four inspection gates that enforce the drawing are on the QC standards page, and the questions that flush out a supplier who quotes one capacity and ships another are in how to evaluate a China packaging supplier. Minimums for the jar sizes above are on the MOQ index.
Vella is a Guangzhou-based beauty packaging solutions provider — a sourcing partner working with vetted partner factories operating to ISO 22716 / GMP — and fixes nominal, brim-full and fill line together in module 1 of every jar specification, so the filling line and the shelf agree. The size range is on cosmetic jars, thick-wall black glass on matte black glass jars, and a cream planned with its serum and oil on skincare packaging solutions.
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