Reservoir Volume & Top-Off Calculator
Turn tank dimensions into gallons and liters, then plan top-offs by blending EC or finding how much water reaches a target EC.
Actual water level. Leave a few inches of headroom.
RO is about 0. Tap is usually 0.2 to 0.6.
Blend mode: what EC do I get after adding this much?
Target mode: how much water hits this EC?
Water in tank
0.0
gal
0 liters
- Full tank capacity
- 0.0 gal (0 L)
- Percent full
- 0%
- Gallons per in of height
- 0.00 gal
- Water weight (filled)
- 0 lbs
EC after adding 0 gal
0.00
mS/cm
New volume 0 gal
- Water to reach target EC
- Volume after that top-off
How this is calculated
Rectangular volume = length × width × fill height. Round volume = π × (diameter ÷ 2)² × fill height. 231 cubic inches per US gallon, 1,000 cm³ per liter, 3.785 liters per gallon, water weighs 8.34 lbs per gallon. Top-off blend EC = (current volume × current EC + added volume × water EC) ÷ total volume. Water needed to hit a target EC = current volume × (current EC − target EC) ÷ (target EC − water EC). Nutrients in solution are treated as fully mixed and EC as linear with dilution, which is close but not exact at high concentrations.