Measure internal dimensions and actual water height
The calculator assumes a rectangular tank. Multiply its internal dimensions in centimeters and divide by 1,000 for liters. Replace total height with water height for the filled-space volume. Glass thickness is not automatically deducted from external dimensions.
This worked example uses internal dimensions of 60 × 30 × 36 cm, a 31 cm waterline, 5 cm of soil, 5% decor displacement, and 12 kg for the empty tank, decor, and equipment together. These are example inputs, not measurements from a real user's tank or a product test. Select cm for this example; the English page initially uses inches.
- Volume in liters = length × width × height in cm ÷ 1,000
- Inch inputs are converted using 2.54 cm per inch
- Water height is limited to tank height; substrate height is limited to water height
Why the whole substrate layer is not deducted
Water occupies some spaces between substrate particles. The tool multiplies the layer's geometric volume by a displacement factor to estimate its solid part. A separate kg/L factor estimates substrate weight.
These factors are assumptions of Baro Tool's model, not certified constants or measured specifications for every product. Grain size, compaction, and material change the real result. Prefer product weight data and recorded fill quantities when available.
| Substrate | Displacement factor | Layer weight factor |
|---|---|---|
| None | 0 | 0 kg/L |
| Sand | 0.65 | 1.5 kg/L |
| Gravel | 0.55 | 1.4 kg/L |
| Soil | 0.50 | 0.75 kg/L |
Reproduce the 60 cm example step by step
Decor percentage applies after substrate displacement, not to gross tank capacity. The calculation limits decor percentage to 0–50%.
Intermediate values retain their precision and the display rounds to one decimal place. Subtracting already-rounded display values can introduce a small difference. The internal 48.735 L result appears as 48.7 L.
| Step | Calculation | Before display rounding |
|---|---|---|
| Gross capacity | 60 × 30 × 36 ÷ 1,000 | 64.8 L |
| Filled space | 60 × 30 × 31 ÷ 1,000 | 55.8 L |
| Soil layer volume | 60 × 30 × 5 ÷ 1,000 | 9 L |
| Substrate displacement | 9 × 0.50 | 4.5 L |
| Decor displacement | (55.8 − 4.5) × 5% | 2.565 L |
| Estimated water volume | 55.8 − 4.5 − 2.565 | 48.735 L |
Water weight and setup weight are different outputs
Water weight approximates one liter as one kilogram. Setup weight adds water, estimated substrate weight, and your entered empty-tank, decor, and equipment weight. The example has 9 × 0.75 = 6.75 kg of estimated soil. Its setup weight is 48.735 + 6.75 + 12 = 67.485 kg, displayed as about 67.5 kg.
A decor displacement percentage does not automatically supply the weight of wood or rocks. Include those measured weights in the empty-tank/decor/equipment field. Do not include substrate a second time, since the tool already estimates it separately.
Stand weight, load distribution, and floor structure are outside the model. The displayed setup estimate is not a structural safety decision. Check support specifications and the installation site's requirements independently.
Compare changes in waterline and decor assumptions
With all other example inputs unchanged, 0% decor gives 51.3 L and 10% gives 46.17 L. Compare those values with the 5% result to understand sensitivity to decor estimates. Actual fill records determine which assumption fits the tank.
Keeping 5 cm soil and 5% decor but lowering the waterline to 30 cm gives (54 − 4.5) × 0.95 = 47.025 L, a reduction of 1.71 L. Testing alternative assumptions is more informative than treating a complex piece of wood as an exactly known volume.
Thirty percent of the original 48.735 L is 14.6205 L, displayed as 14.6 L. This is an amount calculation, not a recommendation to change 30% for a particular species. Product instructions determine whether a conditioner or medication uses replacement-water or total-system volume.
How the equipment reference figures are calculated
The heater estimate multiplies water volume by a W/L factor selected from temperature difference: 0.5 up to 3°C, 0.75 up to 5°C, 1.25 up to 10°C, and 1.75 above 10°C. It rounds upward to a listed heater size. In this example, a 5°C difference gives 48.735 × 0.75 = 36.55125 W, displayed as 50 W.
Filter ranges multiply volume by the model's assumed hourly turnovers: 4–6 for general freshwater, 3–5 for planted tanks, 6–10 for goldfish/high waste, and 8–12 for marine. The freshwater example gives approximately 194.9–292.4 L/h.
These are simplified comparison starting points. The model does not compute actual heat loss, media restriction, hose/head losses, or species-specific requirements. Check manufacturer specifications and installation conditions before choosing equipment.
Use real records to identify model limits
For a new setup, record each measured container of water and the final waterline. Compare that record with the estimate. Without such a record, label the result as estimated volume. Sumps and external canister water are not automatically included in this rectangular-tank calculation.
Substrate height is capped at water height, including for the model's weight estimate. A setup with substantial substrate above the waterline therefore needs a separate substrate-weight measurement. Unusual tank shapes, steep substrate slopes, exposed decor, and external equipment need additional measurements.