One of the most overlooked aspects of supplement shopping is capsule size. Most brands never mention it, leaving consumers to discover at home that their “1 capsule daily” supplement requires swallowing something the size of a small finger.
At ROOK, we believe transparency extends to the physical experience of taking a supplement. Here’s what you need to know about standard capsule sizes.
Standard Capsule Size Chart
| Size | Length (mm) | Diameter (mm) | Volume (mL) | Typical Use |
|---|---|---|---|---|
| Size 4 | 14.3 | 5.3 | 0.21 | Small-dose vitamins |
| Size 3 | 15.9 | 5.8 | 0.30 | Single-ingredient vitamins |
| Size 2 | 18.0 | 6.4 | 0.37 | Standard vitamins |
| Size 1 | 19.4 | 6.9 | 0.50 | Multi-ingredient formulas |
| Size 0 | 21.7 | 7.6 | 0.68 | Standard supplements |
| Size 00 | 23.3 | 8.5 | 0.91 | Larger dose supplements |
| Size 00E | 25.3 | 8.5 | 1.02 | Extended length, same width as 00 |
| Size 000 | 26.1 | 9.9 | 1.37 | Maximum standard size |
Note: Sizes 00E and 000 can be difficult for some people to swallow. If you have difficulty with larger capsules, look for products that use Size 0 or smaller, even if it means taking more capsules per serving.
Why Capsule Size Matters
Dosing flexibility. A product using Size 0 capsules with a 1-capsule serving gives you less flexibility than a product using Size 0 capsules with a 2-capsule serving. The latter lets you take half a dose if needed.
Comfort. Not everyone can comfortably swallow a Size 00 or 000 capsule. This is especially relevant for elderly consumers, children (where appropriate), and anyone with dysphagia.
Ingredient density. Some ingredients are bulky. Magnesium bisglycinate chelate, for example, has a low ratio of elemental magnesium to total chelate weight. Delivering a meaningful dose requires either larger capsules or more capsules per serving.
ROOK Capsule Sizes
We chose our capsule sizes to balance dosing efficacy with swallowing comfort:
| Product | Capsule Size | Serving Size | Why This Size |
|---|---|---|---|
| Iron Bisglycinate + Vitamin C | Size 0 | 1 capsule | Iron + Vitamin C fits comfortably in a standard capsule |
| Magnesium Bisglycinate | Size 00 | 2 capsules | Chelated magnesium is bulky; 2 capsules deliver 200mg elemental Mg |
| Glycine | Size 00 | 3 capsules | 3g of glycine requires volume; 3 capsules at the clinically studied dose |
We could have used fewer, larger capsules (Size 000) for our Magnesium and Glycine products. We chose not to, because swallowing comfort matters more than a “1 capsule daily” marketing claim.
The Bottom Line
Ask about capsule size before you buy. A supplement is only effective if you actually take it — and that starts with being able to swallow it comfortably.
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.