Free aquarium tools
Aquarium & pond calculators
Everything a UK fishkeeper needs in one place - work out tank volume, heater wattage, filter flow rate, substrate and liner sizes, ammonia dosing for a fishless cycle, universal liquid dosing, target-PPM chemistry and more. Every calculator runs in your browser, no sign-up, no email, no ads.
Setup & Sizing
Work out tank/pond volume, heater wattage, flow rate, substrate and liner sizes.
Water Volume Calculator
Quick rectangular tank volume from length, width and height in centimetres.
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Fish Tank Volume Calculator
Shape-aware aquarium volume for rectangular, cylindrical and spherical tanks. Outputs litres, UK gallons and US gallons.
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Pond Volume Calculator
Estimate how many litres or gallons your rectangular, round or kidney pond holds.
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Pond Liner Calculator
Work out the right pond liner size from pond length, width and depth with a 30 cm safety overlap built in.
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Heater Size Calculator
Get a recommended aquarium heater wattage from your tank volume and the temperature offset you need to hold.
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Filter Flow Rate Calculator
Find the filter turnover (litres per hour) you should be aiming for based on tank volume and stocking style.
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Sand Calculator
Calculate how many kilograms of sand or fine gravel you need for a given substrate depth.
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Live Rock Calculator
Estimate the kilograms of live rock to start a reef or marine tank, based on standard stocking rules.
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Lighting
Match lighting power to your plant selection and tank depth.
Dosing & Chemistry
Fishless-cycle ammonia, universal liquid dosing and target-PPM chemistry helpers.
Ammonia Dosing Calculator
Work out the millilitres of household ammonia (or similar) to dose a fishless cycle to a target ppm.
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Universal Dosing Calculator
Scale any liquid aquarium product (ferts, dechlorinator, treatments) to your exact tank volume.
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Potassium (K) Calculator
Estimate grams of potassium sulphate needed to reach a target K PPM for planted aquariums.
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Why use our calculators?
Built for UK fishkeepers
Metric-first inputs with UK & US gallons where they're useful. Dosing maths follows the rules every UK fishless-cycle guide uses.
Nothing hidden
Every calculator shows the formula it uses and a worked example. You can check the maths yourself, or learn why the result is what it is.
Always free
No sign-up, no tracking cookies inside the calculators, no daily limits. Bookmark what you need and share it with the forum when a question comes up.