How to size an oxygen absorber
An oxygen absorber protects dry goods by pulling the oxygen out of the sealed air around them — stopping oxidation, rancidity, mold, and pantry pests. The right size depends on one thing the static charts online never actually compute: how much air is trapped in your package after the product goes in. This calculator does that math.
The steps: measure the internal volume, subtract the space your product occupies to get the residual air, take about a fifth of that (air is 20.9% oxygen) to get the oxygen to remove, then pick an absorber rated at or above it. The practical shortcut most preppers and packers use is to match the absorber's cc rating to the residual air volume — that intentionally over-provides, and extra capacity is harmless.
Common absorber sizes by bag
These are typical starting points for full mylar bags of dense dry goods; use the calculator above for your actual fill.
| Bag / container | Typical residual air | Common absorber |
|---|---|---|
| Quart mylar (dense grain) | low | 100–300 cc |
| 1-gallon mylar (dense) | moderate | 300–500 cc |
| 1-gallon mylar (light/fluffy) | high | 500–1000 cc |
| 5-gallon bucket liner | very high | 1500–2000 cc |
Rules of thumb are a starting point, not a spec — a bag of whole beans traps far less air than the same bag of puffed snacks. Compute yours above, and remember the absorber only works inside a truly airtight, high-barrier bag.
Questions
What size oxygen absorber do I need?
Size it to the residual air in the sealed package: internal volume minus the space your product occupies. Oxygen is about 20.9% of that air, so the absorber needs to capture at least that much oxygen. The common practical rule is to match the cc rating to the residual air volume, which over-provides slightly and is harmless. The calculator above works it out from your dimensions and fill level.
Are oxygen absorbers rated by oxygen or by air?
They are rated by the cubic centimeters of oxygen they can absorb, not air. Because air is only about one-fifth oxygen, a 100 cc absorber can handle roughly 475 cc of air. Many charts quietly size to air volume anyway because it builds in a safety margin, which is why this tool shows both the residual air and the oxygen-only minimum.
Can I use multiple oxygen absorbers together?
Yes. Absorber capacity adds up, so two 500 cc absorbers equal one 1000 cc. Using several smaller absorbers is a common and reliable way to hit a large rating, and slightly over-provisioning does no harm.
Do oxygen absorbers work in any bag?
No. They only work inside a genuinely airtight, high-barrier package such as a foil or metallized mylar bag with an intact heat seal. In a permeable bag, or one with a channel leak in the seal, oxygen keeps entering and the absorber is quickly exhausted. Always verify the seal.
Does the calculator give me a price?
No, it sizes the absorber, not the cost. It computes residual air, oxygen to remove, and the recommended cc rating from your container dimensions and fill level, then rounds up to a standard absorber size.
Need the bag, not just the absorber?
PackOS quotes high-barrier mylar and stand-up pouches from your spec — upload a file or start from scratch.