Free calculators

Aquarium tools

Handy calculators to help you set up and manage your planted tank β€” all instant, all free, no account needed.

πŸͺ£ Tank volume πŸͺΈ Substrate calculator 🟒 COβ‚‚ cylinder runtime πŸͺΈ Substrate calculator 🎨 Drop checker guide
πŸͺ£

Tank volume calculator

Calculate the water volume of any tank shape, with a fill level adjustment. Results feed directly into AquaCalc's dashboard.

Tank shape
Length (cm)
Width (cm)
Height (cm)
Fill level (%)
90%
Substrate depth (cm)
Gross volume
β€”
litres
Net water volume
β€”
litres (fill + substrate)
US gallons
β€”
US gal
UK gallons
β€”
UK gal
Rectangle formula
Length Γ— Width Γ— Height Γ· 1000 = litres
πŸ’‘ Use this in the dashboard
Enter your net water volume as the Tank volume in the pH Monitor tab. Add your filter volume separately to get the total system volume for accurate calculations.
🟒

COβ‚‚ cylinder runtime estimator

Estimate how many days your COβ‚‚ cylinder will last based on injection rate and photoperiod β€” so you're never caught off guard.

Cylinder size
COβ‚‚ remaining (g)
Weigh your cylinder and subtract the empty tare weight (printed on the valve). Or enter your full cylinder weight if new.
Bubble rate
COβ‚‚ on per day (hrs)
Diffuser efficiency
Days remaining
β€”
days
Run out date
β€”
estimated
Daily usage
β€”
g COβ‚‚/day
Reorder by
β€”
allow 7 days buffer
How we estimate usage
Bubble rate Γ— ml per bubble Γ— hours per day Γ— diffuser efficiency gives daily COβ‚‚ volume (ml). COβ‚‚ density at standard conditions is ~1.96 g/L, so we convert ml to grams and divide your remaining COβ‚‚ by daily usage. Actual runtime varies with water temperature, pressure and regulator stability β€” treat this as a guide and reorder before the warning date.
πŸͺΈ

Substrate calculator

Calculate exactly how much substrate you need for any tank shape and depth β€” with bag estimates for popular brands.

Tank dimensions
Tank shape
Length (cm)
Width (cm)
Substrate depth
Layout style
Depth (cm)
Substrate type
Substrate
Volume needed
β€”
litres
Weight needed
β€”
kg
Bags needed
β€”
bags
Spare in last bag
β€”
L leftover
ADA Amazonia
9L bag · Bulk density ~0.70 kg/L · Nutrient-rich aquasoil for planted tanks. Buffers pH down.
πŸ’‘ Sloped substrate tip
Many aquascapers slope substrate from ~3cm at the front to 8–10cm at the back. This creates depth, improves plant root space at the rear and makes the tank look larger. Switch to Sloped layout above to calculate for this style.
πŸ’‘ Use with volume calculator
Your substrate depth reduces net water volume. Once you know your substrate depth, enter it into the Tank volume calculator above to get accurate water volume for CO² and dosing calculations.
🎨

Drop checker colour reference

Enter your reference solution KH and see exactly what colour your drop checker should show at every COβ‚‚ level β€” personalised to your water.

Reference solution KH (dKH)
How to read your drop checker
The indicator solution (bromothymol blue) changes colour based on the pH of the reference water inside the drop checker β€” which is driven by COβ‚‚ diffusing through the air gap. The KH of your reference solution determines the relationship between colour and COβ‚‚ ppm β€” this is why using the standard 4 dKH reference solution gives consistent, comparable results across different tanks and tap water conditions. The drop checker lags 1–2 hours behind actual tank COβ‚‚ levels, so use it alongside AquaCalc's real-time pH monitoring for the most accurate picture.