Protein Skimmer Size Calculator

Why skimmer ratings are optimistic

Manufacturers rate a skimmer at its best case — a lightly-stocked, lightly-fed tank. Load the same tank with a full fish list and heavy feeding and that skimmer is suddenly undersized. That's why the reef rule of thumb is "buy a skimmer rated for roughly double your display volume." We do that math for you: we take the manufacturer's number and derate it by your bioload (heavy ≈ 50% of the rated number, medium ≈ 70%, light = as-rated), or use the manufacturer's own light/medium/heavy breakdown when they publish one.

Bigger isn't always better

An oversized skimmer on a lightly-fed tank can skim too aggressively and go unstable (constant overflowing or nothing at all). Aim for a skimmer whose derated rating comfortably covers your tank — not one rated for triple. The smallest model that clears your number is usually the right buy.

Check the footprint and water depth

The best-rated skimmer is useless if it won't fit your sump. Two specs decide that: the skimmer's footprint (it needs to sit in your skimmer chamber) and its recommended water depth — run it too deep or too shallow and it won't skim right. Every skimmer below lists both.

In-sump vs. hang-on-back vs. nano

In-sump skimmers are the standard for any tank with a sump — best performance and quiet. Hang-on-back (HOB) skimmers are for tanks without a sump. Nano/AIO skimmers are purpose-built for all-in-one tanks under ~40 gallons. Filter by type above to see only what fits your setup.