Capsule Sizes Explained: A Complete Guide for Supplement Brands

Most brands don't think about capsule size until it's a problem. The formula is finalized, the dose is set, and then someone asks: does this actually fit in a capsule anyone wants to swallow? Capsule size determines how much active ingredient fits per capsule, how comfortable the finished product is to take, and how the product looks and costs on the shelf.

Get it wrong, and you're reformulating late, splitting doses you didn't plan for, or absorbing costs you didn't budget. Get it right early, and the rest of development gets easier. This guide walks through the standard capsule sizes, how to read a capsule size chart, how to choose the right size for your formula, and what to confirm with a capsule manufacturer before you commit.

The Standard Capsule Size Scale

Two-piece capsules are made in a set of standard sizes, and the numbering trips people up the first time they see it: the sizes run from the largest, 000, down through 00, 0, 1, 2, 3, 4, and 5, with larger numbers denoting smaller capsules. In other words, the relationship is inverted from what most people expect. A size 000 capsule is the largest standard size commonly used in supplements, and a size 5 is the smallest. Everything in between (00, 0, 1, 2, 3, and 4) steps down in capacity in a fairly predictable progression.

Each size corresponds to a fixed internal volume, measured in milliliters, and that volume is what actually determines how much powder, granulate, or pellet blend can go inside. A 000 capsule holds roughly 1.37 mL. A 00 holds about 0.91 mL. A 0 holds around 0.68 mL, a 1 about 0.50 mL, a 2 about 0.37 mL, a 3 about 0.30 mL, a 4 about 0.21 mL, and a 5 about 0.13 mL. Those volumes are fixed by the capsule shell's dimensions, which is why capsule sizes are standardized across manufacturers in the first place: a 00 capsule from one supplier is dimensionally interchangeable with a 00 from another.

Volume, though, is not the same thing as fill weight, and this is where a lot of confusion sets in. The volume of a capsule is constant. What varies is how much a given ingredient blend weighs when it fills that volume, because density differs enormously from one powder to the next. A dense mineral chelate packs far more milligrams into the same 0.68 mL cavity than a light, fluffy botanical extract does. This is why two different products in the same size 0 capsule can have wildly different fill weights, and it's also why "how much fits in a 00 capsule" doesn't have one universal answer. It depends on what you're filling it with.

It's also worth knowing that the numbering convention is standardized across the industry, but real-world dimensions carry small manufacturing tolerances from one shell supplier to another, and elongated versions of some sizes (a 00 elongated, for example) exist specifically to add volume without moving to the next size up. That's a useful middle option when a formula falls just short of fitting a standard 00 but doesn't need the full jump to a 000. A capsule manufacturer with real formulation experience will usually flag this option rather than defaulting straight to the next size on the standard scale.

Capsule Size Chart

The table below gives approximate volumes and typical fill-weight ranges for the standard sizes used in supplement manufacturing. Treat the fill-weight figures as a starting point, not a guarantee: they assume a mid-range powder density, and your actual formula may fill heavier or lighter depending on the ingredients involved.

*Fill weights are approximate and density-dependent. A dense, granular blend will fill toward the higher end of the range for its size; a light, low-density powder will fill toward the lower end, or may not reach the minimum practical fill at all.

Two sizes worth calling out because they show up constantly in supplement formulation: 00 is the workhorse size for single-active or moderately dosed formulas, since it's large enough to carry a meaningful fill weight but still swallowable for most adults, and 0 is the common step-down when a formula is dose-flexible or when the brand wants a slightly smaller, easier-to-swallow capsule without cutting the active dose by much.

Size 000 capsules tend to appear in high-dose, single-ingredient products (a full-spectrum greens blend or a high-dose mineral, for example) where the volume is simply necessary to hit the label claim in one capsule.

How to Choose the Right Capsule Size

Choosing a capsule size isn't a guess, and it isn't purely a matter of picking whatever looks standard. It's a calculation that starts with the formula and works outward.

Start from the dose. The required amount of active ingredient per serving is the anchor point for everything else. If your formula calls for 500 mg of a single active per serving, that figure, combined with the density of that ingredient, tells you the minimum volume you need, which points you toward a specific size or a specific number of capsules per serving. Trying to force a high dose into a small capsule doesn't work; the ingredient simply won't fit, however much a brand might prefer the smaller format.

Account for excipients and density. Very few capsules contain only the active ingredient. Flow agents, binders, disintegrants, and sometimes fillers all take up room inside the capsule, and their combined density with the active ingredient is what actually determines the final fill weight, not the active ingredient's density alone.

A formula heavy on excipients will need more room per milligram of active than a clean, single-ingredient fill. This is one of the most common surprises brands run into during scale-up: a bench formula that fit comfortably in a 0 capsule needs a 00 once the full excipient profile is finalized, because a flow agent that was negligible at small batch sizes behaves differently once the blend is running through production equipment at volume. Multi-ingredient blends compound this further.

A formula combining several botanicals, a mineral, and a flow agent has to account for the density of the whole mixture, not any single component, which is why bench-scale density estimates should always be confirmed with an actual encapsulation trial before a size is finalized on paper.

This is exactly the kind of check an in-house analytical laboratory is built for. A manufacturer that can test identity, potency, purity, and stability on-site can confirm a fill-weight assumption in days rather than waiting on results from a third-party lab.

Balance capacity against swallowability. The largest capsule sizes (000 and, to a lesser degree, 00) hold the most, but they're also the hardest for many consumers to swallow comfortably. Pill fatigue and swallowing difficulty are real reasons consumers stop taking a supplement, so pushing every formula toward the biggest available size purely because it offers more room isn't necessarily a win. If your target consumer skews toward people who already take multiple capsules a day, or toward an older demographic, that swallowability tradeoff deserves real weight in the decision, not an afterthought.

Consider splitting the dose across two capsules. When a single serving genuinely doesn't fit comfortably into a size most consumers can swallow, splitting the dose across two smaller capsules is often the better answer, rather than defaulting to the largest available shell.

Two 0 capsules can be easier to take than one 000, even though the total volume delivered is similar, and the smaller capsules also read as less intimidating on a label and in hand. This is a legitimate formulation choice, not a compromise, and it's worth discussing with your manufacturer before you lock in a single-capsule target.

Gelatin vs. Vegetable Capsules, Briefly

Size isn't the only variable in play. The shell material matters too, and it interacts with size in ways worth knowing about even in a guide focused on sizing. Gelatin and vegetable (typically HPMC-based) capsules have slightly different characteristics around moisture sensitivity, disintegration, and formulation flexibility, and the right choice depends on your ingredients and your brand positioning as much as it depends on capsule size.

We've covered that comparison in depth in a separate post (see our guide to gelatin vs. vegetable capsules for the full breakdown), but the short version for this guide is that both shell types are available across the standard size range, so choosing a shell material doesn't meaningfully limit your size options.

What to Confirm With Your Capsule Manufacturer

Once you have a size range in mind, a short conversation with your manufacturer should confirm a few things before you finalize anything. Family-owned capsule manufacturers with decades of encapsulation experience (Rasi Labs has been running this exact conversation with brands since 1984) tend to give straighter answers here than a broker working across multiple contract facilities:

• That they run your chosen size in-house. Not every capsule manufacturer runs every size on every filling line. Confirm the specific size you need is one they encapsulate routinely, rather than something they'd need to special-order or subcontract. A manufacturer running production inside a HEPA-equipped facility with laminar air flow in every process suite, and with refrigerated vaults available for temperature-sensitive actives, has more flexibility to run your formula exactly as specified rather than working around facility limitations.
• That they can advise on size based on your formula and fill weight. A manufacturer with real capsule expertise should be able to look at your formula, your target dose, and your ingredient densities, and tell you where you're likely to land on the size chart, and flag early if your target dose and your preferred capsule size aren't compatible.
• That they offer the shell material your positioning requires. If your brand is committed to a plant-based or clean-label position, confirm your manufacturer offers vegetable capsules in the size you need, not just gelatin. The reverse is true too: if cost or specific disintegration characteristics point you toward gelatin, confirm that's available in-house as well.

These are simple questions, but they're worth asking before a formula is finalized rather than after. A manufacturer who can't run your target size in-house, or who only stocks one shell material, will either push you toward a size or material that doesn't fit your formula or your brand, or add time and cost to source what you actually need. Getting a straight answer on all three points up front saves a renegotiation later in development.

Conclusion

Capsule sizes look like a small, late-stage decision, but they touch dose, swallowability, cost, and shelf appearance all at once. That's exactly why it's worth getting the sizing right early rather than discovering a mismatch after your formula is locked. Use the standard size scale and the capsule size chart above as your starting reference, but treat the fill-weight numbers as a guide, not a substitute for testing your actual formula. From there, the fastest way to land on the right size is to work with a capsule manufacturer that can look at your formula and fill weight and tell you, specifically, what will and won't work, rather than pointing you toward whatever size happens to be easiest for them to run.

At Rasi Labs, capsule sizing conversations like this happen early and often, out of our 200,000-square-foot facility on 37 company-owned acres in Cranbury, New Jersey, and under triple certification as an NSF-certified, cGMP-compliant, FDA-registered manufacturer. We manufacture custom two-piece capsules across the full range of standard sizes, in both gelatin and plant-based shells, and we don't offer private label manufacturing.

Every formula we produce is developed exclusively for the client who owns it, sized to that client's specific dose and fill weight from the start. If you're weighing capsule size decisions for a new or reformulated product, our supplement manufacturer page walks through how we approach formulation and manufacturing from the ground up.