Your 75 gallon tank doesn't hold 75 gallons.

Set up with sand and a sensible gap at the top, it holds about 65. Most fishkeepers never find that out, so they dose medication, choose heaters and plan their fish on a number that's around 15% too high.

I'm Sumeet Joseph Desilva, and I built TankRatio to fix that.

When I started comparing tanks, the numbers disagreed everywhere I looked. The label says 75. The outside measures 82. Two of the biggest makers list full weights 70 lb apart. Search answers quote a weight neither maker gives, and some mix aquarium tanks up with RV water tanks. None of those are small differences when you're choosing a stand for a floor, or working out a dose for a sick fish.

So every number here has to earn its place

• Sourced. Tank sizes come from the makers' own published specs, and every page links to them.
• Shown. The formula sits on the page, next to worked examples I've checked by hand.
• Honest about uncertainty. When brands disagree, you see both figures and why. When something is an estimate, it says so.
• Yours to use. Free, no sign-up. Every result has a link you can share and a calculator you can embed on your own site.

Spot something wrong?

Email [email protected]. Corrections to the numbers jump the queue, because a calculator is only worth using if you can trust it.

How the site is funded

TankRatio may earn a commission from some product links and, later, from display ads. That never changes a calculation or which size we suggest. See the affiliate disclosure.