Protein Skimmer Size Calculator
A protein skimmer size calculator determines the right skimmer rating for your reef tank based on total water volume and bioload. Enter your display and sump gallons, pick a bioload, and get a recommended rated tank capacity range and skimmer type.
Tank Volume
Enter your display and sump capacity
Bioload
How heavily is your tank stocked and fed?
Stocking Style
What kind of reef are you running?
Recommended Skimmer Size
Skimmer Sizing Tips
- ✓Manufacturer ratings are optimistic. Most skimmer ratings assume light stocking. Treat the rated capacity as an upper bound, not a target.
- ✓Plan for the future. A grow-out tank with juvenile fish becomes a heavy bioload tank in 2-3 years. Size for where you are headed, not where you are now.
- ✓Skimmer body diameter matters more than rating. A larger reaction chamber and bigger pump produce more skimmate than a tiny skimmer with an inflated rating.
- ✓Check your sump footprint. Before buying, measure the skimmer section of your sump. Many oversized skimmers are taller and wider than reefers expect.
- ✓Break-in takes 2-4 weeks. A new skimmer will not produce stable skimmate immediately. Resist the urge to swap or return until it has cycled in.
How It Works
- 1Add display + sump volume. The calculator sums display and sump gallons, then subtracts ~10% for rock and sand displacement to get net water volume.
- 2Apply a bioload factor. Light bioload multiplies by 1.5x, medium by 2x, heavy by 3x. This gives the target rated tank capacity for the skimmer.
- 3Add a 15% safety margin. The output is a range from -15% to +15% around the target. Picking a skimmer near the top of the range is safer than the bottom.
- 4Match the skimmer type. Tank size also determines what kind of skimmer fits: HOB or in-tank for nano, in-sump cone or recirculating for mid-size, recirculating or external for large systems.
Frequently Asked Questions
What size protein skimmer do I need for my reef tank?
Add display tank volume to sump volume, then subtract about 10 percent for rock and sand displacement. Multiply that net water volume by 1.5x for a light SPS bioload, 2x for a typical mixed reef, or 3x for a heavy FOWLR bioload. The result is the rated tank capacity to look for on a skimmer. For a 100 gallon system with a mixed reef, you want a skimmer rated for roughly 180 gallons.
Should I oversize my protein skimmer?
Yes, in almost every case. Skimmer manufacturer ratings are optimistic and usually assume a light bioload. An oversized skimmer can be tuned wetter or drier as needed, while an undersized skimmer cannot keep up with heavy feeding or full grow-out fish loads. Reefers commonly run a skimmer rated 1.5x to 2x their actual water volume.
How do you calculate protein skimmer size?
Total water volume equals display gallons plus sump gallons, minus roughly 10 percent for rock and sand displacement. Multiply that by a bioload factor: 1.5x for light, 2x for medium, 3x for heavy. The product is the minimum rated tank capacity for the skimmer. Most reefers add another 15 percent on top as a safety margin and pick a skimmer near the high end of the resulting range.
What is rated tank capacity on a protein skimmer?
Rated tank capacity is the total system water volume the manufacturer claims a skimmer can effectively process under typical conditions. Because manufacturers often base the number on light bioload, treat it as an upper bound rather than a target. Match a skimmer's rated capacity to your actual water volume multiplied by a bioload factor.
Do I need a protein skimmer for a 75 gallon reef tank?
A protein skimmer is strongly recommended for any reef tank 30 gallons and up, including a 75 gallon. Skimmers export dissolved organics before they break down into nitrate and phosphate, which keeps water cleaner for corals. For a 75 gallon display with a 20 gallon sump, look at a skimmer rated for 130 to 200 gallons depending on bioload.
Track Your Tank Parameters and More
Track your tank parameters and more with My Reef Log - a free reef keeping journal. Log water tests, visualize trends, manage livestock, and never miss a maintenance task.
Start Tracking FreeNo credit card required