About TankMath & calculation sources

TankMath makes freshwater tank planning arithmetic easy to inspect. It does not sell a stocking limit or certify a stand.

How the estimates work

Tank names are nominal capacities. Rounded glass-tank dimensions describe representative footprints, not a current product specification. Brands, frames and product generations differ, often by about half an inch and sometimes more. Measure the inside for water and substrate and the outside for a stand or lid.

Volume divides cubic inches by 231, then multiplies gallons by 3.78541 for litres. A working fill of 85% is a rough assumption, not a measurement. Water-change plans use 85% of nominal; volume plans use 85% of the calculated rectangle.

Substrate assumes bulk densities of 100 lb/ft³ for gravel and sand, and 60 for aquasoil. These are shopping estimates; use a bag’s stated volume or coverage when available. Surface-area stocking budgets of 30, 45 and 60 in² per adult inch are illustrative comparisons, not evidence-based fish limits. Check species needs separately.

Heater and filter ranges are rules of thumb. The 3/4/5 W per gallon temperature bands are planning choices, not a thermal simulation. Glass weight estimates use five rectangular panes, assumed thickness and density, without frames or bracing. They are not aquarium construction specifications.

Sources and verification

• NIST conversion tables
• Aqueon size chart
• Seachem Prime directions
• Fluval heater guidance
• Aqueon water maintenance
• Water density reference

Prime’s standard US-gallon dose was checked against Seachem’s directions on November 3, 2026. No API product concentration is assumed. Enter the ratio on your own bottle for other products. Treat replacement water separately when using a replacement-water dose; direct-to-tank Prime directions use aquarium volume.

Water is rounded to 8.34 lb per US gallon; its density varies with temperature. Turnover ranges are circulation starting points, and real filter flow depends on media, lift and maintenance. Fish health and water tests determine whether the setup is working.

Affiliate links

Some product links go to Amazon. As an Amazon Associate I earn from qualifying purchases. It does not change the price you pay or the calculations.

Corrections

Send a measurement, formula correction or broken link to glitchyprojects@gmail.com.