Size 0 empty capsules: how to choose, fill, and use them effectively

What are size 0 empty capsules?

Size 0 empty capsules are hard-shell oral dosage containers with an internal volume of approximately 0.68 mL, capable of holding roughly 400–540 mg of powder depending on ingredient density. They are the single most common capsule size used in the US dietary supplement industry, sitting at the practical midpoint between the oversized size 000 and the smaller size 1.

Understanding the capsule sizing system trips up a lot of newcomers. Why does a higher number mean a smaller capsule? The numbering convention is inherited from pharmaceutical history, not logic. Size 5 is the smallest; size 000 is the largest. Size 0 and size 00 together account for roughly 55% of global capsule consumption, according to industry reports from Lonza/Capsugel — a figure that reflects just how well this size range matches the needs of typical adult supplement formulations.

Size 0 empty capsules are defined as: two-piece hard-shell capsules (body and cap) in standard pharmaceutical sizing, with a locked length of 21.7 mm, designed for filling with powders, pellets, granules, or small tablets before oral consumption.

For context, a pharmaceutical capsule overview on Wikipedia details how the two-piece hard capsule format has been the dominant oral solid dosage form since the 1800s — the size 0 variant in particular became the standard for single-herb and combination supplement products throughout the US market.

How size 0 compares to neighboring sizes

Most buyers arrive at size 0 after ruling out alternatives. Size 00 holds more — about 0.91 mL — but some users find it difficult to swallow. Size 1 holds only 0.50 mL, which simply isn't enough for many standard herbal doses. Size 0 hits the sweet spot: large enough for a meaningful dose, small enough that most adults can swallow it without difficulty.

Actual fill volume also depends on whether you're using standard capsules or elongated (EL) variants. Some manufacturers offer a size 0 EL format with slightly increased body length, boosting fill capacity by roughly 10–15% while keeping the same cap diameter — useful when you need more milligrams without stepping up to a 00.

Who typically buys size 0 empty capsules?

In 2026, the primary buyer segments for size 0 empty capsules in the US are: home DIY formulators making custom herbal or vitamin blends, small supplement brands producing in batches under 10,000 units, naturopathic practitioners dispensing custom compounds, and research labs handling small-scale encapsulation. Each segment has slightly different requirements — a home user prioritizes ease of hand-filling, while a small brand needs machine compatibility and consistent shell quality across lots.

Size 0 capsule fill weight: how much can it actually hold?

The honest answer: it depends entirely on what you're filling. A size 0 capsule does not hold "500 mg" as a universal rule — that figure assumes a powder density of approximately 0.74 g/cm³, which is roughly true for some powders but wildly off for others. Understanding this distinction is probably the most practically important thing in this entire guide.

Real testing across common supplement ingredients reveals significant variation. Creatine monohydrate, which has a relatively high bulk density (~0.85 g/cm³), packs around 580 mg into a size 0. Turmeric powder, with a lower density (~0.55 g/cm³), may only fill 375 mg. Magnesium glycinate sits somewhere in the middle. If you're designing a formulation and calculating doses, you must measure your specific ingredient's tap density — do not rely on generic estimates.

Table 1: Size 0 capsule fill weight by common ingredient type (approximate values based on typical bulk density)

Ingredient	Bulk density (g/cm³)	Approx. fill weight (mg)	Notes
Creatine monohydrate	~0.85	~578	Dense, free-flowing
Magnesium glycinate	~0.70	~476	Moderate density
Turmeric powder	~0.55	~374	Fluffy, may bridge
Vitamin C (ascorbic acid)	~0.96	~653	Very dense crystalline
Ashwagandha root powder	~0.50	~340	Low density, sticks
Whey protein isolate	~0.38	~258	Very low — size 00 preferred

Why the "500 mg capsule" claim is misleading

You'll see "500 mg capsules" listed on supplement bottles constantly. This refers to the fill weight of that specific formulation — not a universal capacity of the size 0 shell. A size 0 capsule filled with a dense crystalline powder like vitamin C can exceed 650 mg. The same capsule filled with a fluffy herbal extract might hold only 300 mg. Knowing your ingredient's tap density isn't optional if accuracy matters.

Size 0 vs. size 00 capsules: when does the upgrade make sense?

When comparing size 0 vs size 00 capsules, the volume difference is meaningful: 0.68 mL versus 0.91 mL, a 34% increase. That matters when you're formulating something like a fish oil alternative or a high-dose CoQ10 product where softgels aren't an option. However, size 00 hard shells are noticeably longer (23.3 mm locked vs. 21.7 mm), and clinical swallowability studies consistently show that some users — particularly older adults — struggle with anything above 22 mm. Size 0 remains the default choice unless your formulation physically demands more volume.

Gelatin vs. HPMC vs. pullulan: choosing the right shell material

Shell material selection is where many DIY formulators make avoidable mistakes. The choice isn't just about vegetarian preferences — it directly affects dissolution rate, moisture sensitivity, and ingredient stability.

"HPMC capsules dissolve more slowly than gelatin at lower pH values, which can be advantageous for sensitive actives but must be accounted for in dissolution testing. They are not a drop-in replacement for gelatin without formulation review." — Industry formulation guidance, Capsugel/Lonza technical documentation, 2025

Size 0 gelatin capsules: still the industry baseline

Size 0 gelatin capsules remain the most affordable option and the fastest-dissolving hard shell format in standard gastric conditions. Derived from bovine or porcine collagen, they're unsuitable for vegan, vegetarian, halal, or kosher markets without specific certification. Gelatin shells are also more moisture-reactive — they begin to soften and deform at relative humidity above 65%, and they become brittle below 30% RH. For DIY formulators working with dry, stable ingredients in a temperature-controlled environment, they're a perfectly sound choice.

One critical caveat: size 0 gelatin capsules should not be used with highly hygroscopic ingredients — compounds that aggressively absorb moisture from the surrounding environment. If your powder pulls moisture from the shell itself, you'll get a degraded capsule and a clumped fill. This is a common failure mode that almost no beginner-focused content adequately addresses.

HPMC capsules size 0: the right choice for moisture-sensitive formulations

HPMC (hydroxypropyl methylcellulose) capsules, also called vegetarian capsules size 0 or plant-based capsules, have a significantly lower equilibrium moisture content than gelatin — typically 4–6% versus 13–15% for gelatin. This makes them the correct choice for moisture-reactive compounds: hygroscopic mineral salts, certain probiotics, and any ingredient where residual moisture accelerates degradation.

They cost more — typically 20–40% more per unit than comparable gelatin shells at retail quantities. But for the right application, that premium is justified. HPMC capsules are also compatible with a wider range of fill materials, including some liquid fills that gelatin cannot handle. The size 0 clear capsules version in HPMC is popular for supplement products where the customer wants to see the fill material.

Pullulan capsules: when quality certification is the priority

Pullulan capsules are produced from a natural fermentation-derived polysaccharide. They offer the lowest oxygen permeability of any capsule shell material — relevant for oxidation-sensitive actives like astaxanthin or fish oil powders. They're also non-GMO certifiable and appeal to the premium natural products segment. The trade-off is cost: pullulan shells typically run 2–3× the price of gelatin equivalents. Most small-batch producers don't need them unless a specific certification or antioxidant protection requirement drives the decision.

Storing empty capsules before filling: humidity, heat, and shelf life

Here's something the product listings almost never mention: how you store your empty gelatin pill shells before filling has a direct impact on fill quality and capsule integrity. Get this wrong, and you'll encounter capsules that crack during filling, fail to lock properly, or develop visible deformation.

Optimal storage conditions for empty hard capsules

Based on manufacturer specifications from major suppliers, the recommended storage conditions for both gelatin and HPMC empty capsules are: temperature 59–77°F (15–25°C), relative humidity 35–65% RH. Gelatin capsules are more sensitive to the humidity range; HPMC capsules tolerate somewhat wider conditions but still degrade above 75% RH over extended periods.

Practical guidance for US home environments: if you live in a humid climate (Southeast, Gulf Coast), do not store bulk empty capsules in an unair-conditioned garage or pantry during summer. Humidity above 65% RH causes gelatin shells to soften, stick together, and lose their crisp snap when closing. Conversely, in very dry winter conditions (indoor heated air in northern states can drop to 20–25% RH), capsules become brittle and may crack when pressure is applied during filling.

Shelf life and packaging considerations

Unopened, factory-sealed empty capsules typically carry a manufacturer shelf life of 2–3 years for gelatin and 3–5 years for HPMC, stored under recommended conditions. Once opened, both types should ideally be used within 12 months. Store opened bags in a resealable container with a silica gel desiccant packet — this is a small investment that meaningfully extends usability, especially for bulk empty capsules purchased in quantities of 10,000 or more. Never store them in the refrigerator; the condensation cycle when you remove them causes localized high-humidity exposure that accelerates degradation.

Capsule filling machine compatibility for size 0

The capsule filling machine size 0 compatibility question matters more than most buyers realize. Not all machines labeled "works with size 0" perform equally — the fit tolerance of the machine's capsule holder directly affects fill consistency and cap locking success rate.

Home tray fillers: Cap-M-Quik and The Capsule Machine

For home users filling up to a few hundred capsules per session, two tools dominate the US market. The Cap-M-Quik is a simple 50-hole tray system that works reliably with standard size 0 capsules from most major suppliers. Actual testing with various brands confirms it handles both gelatin and HPMC size 0 shells without modification, though HPMC capsules occasionally require slightly firmer pressure to lock due to their stiffer shell material.

The Capsule Machine (by Capsule Connection) uses a 24-hole interlocking plate design. It's slower than Cap-M-Quik per session but produces a tighter cap lock, which some users prefer for fine powders that might otherwise spill if the cap seal is loose. Both tools are sized specifically for size 0 — purchasing the correct size plate is mandatory, as they are not interchangeable with size 00 or size 1 tooling.

Semi-automatic machines for small brands

Small supplement brands producing batches of 1,000–5,000 capsules typically graduate to semi-automatic bench-top encapsulators. These machines use size-specific tooling sets (called "change parts" or "segment sets") and standard size 0 capsules from reputable pharmaceutical suppliers work consistently across these platforms. When ordering bulk capsules for semi-auto use, confirm with your supplier that their capsules meet USP dimensional tolerances — off-spec capsules from low-quality sources cause frequent jams and inconsistent fill weights, which is costly in a production context.

DIY supplement labeling: FDA requirements you can't ignore

This is the area almost no competitor content addresses honestly. If you're filling homemade capsule supplements for personal use only, FDA labeling rules don't directly apply. The moment you share, sell, or distribute your capsules to others — even informally — you enter regulated territory.

Dietary supplement vs. drug: the critical distinction

Under US law, a dietary supplement cannot claim to diagnose, treat, cure, or prevent any disease. If your encapsulated product makes such a claim on its label or in accompanying marketing materials, the FDA treats it as an unapproved drug — a serious regulatory violation. This applies to handwritten labels on jars of homemade capsule supplements just as it applies to commercially printed labels. The FDA's food additive status list is a useful starting reference for verifying that your capsule fill ingredients have recognized safe-use status in the US.

Minimum labeling requirements and cGMP context

For any dietary supplement sold in the US, the label must include: product name, net quantity, ingredient list with amounts per serving, manufacturer or distributor name and address, and a disclaimer stating "This statement has not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease." The FDA's cGMP (current Good Manufacturing Practice) regulations under 21 CFR Part 111 technically apply to all dietary supplement manufacturers, though enforcement intensity scales with production volume and distribution scope.

Of course, there's a practical reality: the FDA does not actively inspect solo home users filling personal-use capsules. But if you're selling at a farmer's market, online, or through a local store — even in small quantities — the regulatory framework applies. Getting this right from the start is far less painful than dealing with it retroactively.

How to buy size 0 empty capsules in bulk: a practical guide

For most DIY users and small producers, buying size 0 empty capsules in bulk is straightforward — but a few purchasing decisions significantly affect value and quality.

Key factors when comparing suppliers

When evaluating bulk empty capsules, prioritize these criteria in order: dimensional consistency (capsules that don't meet USP tolerances cause machine jams and poor fill), material certification (NSF, USP, Halal, Kosher, or vegan certification depending on your market), lot traceability (reputable suppliers provide Certificate of Analysis documents per batch), and price per thousand at your target quantity tier.

1. Confirm the capsule meets USP or equivalent dimensional standards — ask for a CoA (Certificate of Analysis).
2. Choose gelatin for cost efficiency with dry, non-hygroscopic powders; choose HPMC capsules size 0 for moisture-sensitive or vegan formulations.
3. Order a sample pack of 100–500 before committing to a bulk order of 10,000+ — test with your specific fill material and your filling equipment.
4. Compare price per 1,000 units across quantity tiers (1,000 / 5,000 / 10,000 / 50,000) — the price break at 10,000 units is typically 30–50% versus buying in 1,000-unit quantities.
5. Verify the supplier ships in moisture-barrier packaging, especially for gelatin capsules destined for humid climates.

Price benchmarks and what to expect in 2026

As of 2026 data, retail pricing for size 0 empty capsules in the US market runs approximately $8–$14 per 1,000 units for standard gelatin, and $15–$28 per 1,000 for HPMC vegetarian capsules size 0, at quantities under 5,000. At 10,000+ units, gelatin prices drop to roughly $4–$7 per 1,000 and HPMC to $9–$16 per 1,000 from reputable wholesale suppliers. Pullulan capsules remain a premium product at $25–$50 per 1,000 even at moderate volumes.

Why do prices vary so much within the same size and material category? Shell wall thickness, dissolution rate consistency, and lot-to-lot dimensional variance all differ across manufacturers. The lowest-price options on Amazon or eBay frequently come from suppliers who do not publish CoA documents or dimensional specifications — a risk worth avoiding if you're producing capsules for anyone other than yourself.

Clear vs. opaque capsules: functional and marketing considerations

Size 0 clear capsules — transparent shells that show the fill material — are popular in the premium supplement market because they visually demonstrate product quality. Opaque or colored capsules serve two different functions: concealing fill color variation (relevant for consistency in herbal blends where color varies batch to batch) and providing light protection for photosensitive actives like riboflavin or certain plant extracts. Just like sunglasses protect your eyes from UV, opaque capsule shells protect light-sensitive ingredients from photodegradation on store shelves.

For DIY supplement capsules where ingredient appearance is part of the value proposition — a single-origin herb, a distinctive botanical powder — clear gelatin or HPMC shells let the product speak for itself. Either way, the pharmaceutical capsules you choose send a quality signal to whoever is taking them.

Frequently asked questions