A capsule size chart looks like a menu of numbers, but it is really a conversion table between volume and weight. The size number describes the internal volume of the shell; the milligrams it holds depends entirely on how densely the blend packs into that volume. Two brands can pick the same size 0 and deliver 380 mg and 620 mg without either being wrong.
The metric sizes in common use are 00, 0, 1, 2, 3, 4 and the tiny 5 through 12, with 00, 0 and 1 covering most supplement work. The clear and opaque body and cap options do not change capacity, but color and opacity affect light protection and how fill defects show on a line.
Start with the required active weight per dose, then add excipients. A blend usually needs one to three percent lubricant, sometimes a glidant, and often a diluent when the active is a high-potency extract at fifty milligrams. Working out total blend weight is what makes the size choice a calculation rather than a guess.
Bulk density is the missing column on most charts. An extract with a carrier at a low tapped density of 0.35 g/ml occupies nearly double the volume of a mineral salt at 0.7 g/ml. Ask for the tapped and loose density of the actual blend, then compute the fill weight range before confirming a shell size.
Swallowability constrains the top of the range. Size 00 is difficult for a meaningful share of adults, and a product intended for older consumers or a market with low capsule experience should usually start at size 0 or 1. The alternative to a larger shell is more capsules per serving, which is only acceptable if the count is one or two.
Vegetarian shells shift the arithmetic slightly. HPMC shells have a marginally different internal geometry and are more sensitive to low moisture, so the practical fill weight for a very dry, light blend can differ from the gelatin equivalent. If a formula is being converted from gelatin to HPMC, re-verify weight variation rather than assuming equivalence.
Overfilling and underfilling create distinct defects. An overfilled body prevents the cap from seating, producing loose caps and separated units; an underfilled capsule rattles, looks half-empty in a clear shell and reads as a short-dosed product. A specification should state the target weight and the acceptable variation band.
Two-piece versus one-piece hard capsules matter for powder work. Standard supplement production uses two-piece shells filled on machine tooling matched to the shell size, and a machine tool change is needed to move size, which has lead time and cleaning consequences.
Practical checkpoints before finalizing size: weigh a manual fill of ten capsules of the intended size from the actual blend; check the powder flows from a hopper without bridging; confirm the capsule closes with a full lock band; and note the appearance in a clear PET jar with a white background.
Size also affects cost per dose. A smaller shell usually costs marginally less, but a formula requiring three size-1 capsules per serving instead of one size-00 changes pack count, blister cavities and label serving text, and the total unit cost moves more than the shell price did.
Reading a capsule size chart well means treating the size number as the last decision instead of the first. Dose requirement, blend density, excipient share and the swallow profile of the target market determine the size; the chart then converts that into a shell code and a fill weight range worth writing into the specification.
A disciplined order of work avoids a rebuild: required dose per serving, blend composition including excipients, measured tapped density, calculated fill weight, then shell size, then swallowability review against the target consumer. Reversing the sequence and starting from the shell is what produces a formula that is later cut in half to fit.
