Water Tank Volume Calculator
Compute rectangular and cylindrical water tank volume in liters. Suggests minimum size for N people (200L/day/person).
—
Water tank volume and per-capita demand
A rectangular tank holds V = L·W·H m³ (multiply by 1,000 to get liters), while a cylindrical tank holds V = π·r²·h. The Brazilian standard NBR 5626 (building water supply) and SABESP's residential reference both assume something like ~150–200 L per person per day. In practice, though, most people size by a rougher rule: 1,000 L per resident, enough to cover 2 days of consumption. So a 4-person household wants at least 1,000 L of upper tank + 500 L of reserve, which comes to 1,500 L. In buildings there's an extra requirement: NBR 5626 calls for a fire reserve sized according to NBR 13714, usually around 15–20% of the total.
Applications
Sizing tanks for homes and buildings, working out a technical fire reserve, designing autoclave pressurization systems, houses that run a cistern plus an upper tank, and rainwater capture projects (NBR 15527).
FAQ
Upper tank only or with cistern? Where the supply is unreliable, pairing a lower cistern with an upper tank roughly doubles your autonomy. A pump fills the upper tank, and from there gravity feeds the house (1 mwc per meter of height).
How often to clean? ANVISA and the utilities advise a cleaning every 6 months. Sediment and biofilm build up regardless, even under a sealed lid.
Polyethylene, fiberglass or concrete? Polyethylene is the cheap, light option (good up to ~3,000 L). Fiberglass lasts longer. Concrete gets poured in place when you need a big reserve (>5,000 L). Whatever the material, it needs an external lid to keep insects and contamination out.
Related Tools
Fire Water Reserve (RTI)
Calculate the fire water reserve volume, V = flow × time ÷ 1000, multiplying the system's required flow (L/min) by the required autonomy time (min) and converting to cubic metres. The result, in m³, is the water volume the tank must keep reserved exclusively for firefighting — sized to feed hydrants and/or sprinklers for the minimum time set by codes (typically 30 to 60 min, depending on risk). It is a central calculation in building firefighting installation design. Enter the flow and the autonomy time.
Oil Formation Volume Factor (Bo)
Compute the oil formation volume factor (Bo) by dividing the volume the oil occupies at reservoir conditions by the volume it occupies at the surface (stock-tank barrels). Bo is always greater than 1 because, in the reservoir, the oil is hot and has dissolved gas, occupying more space; as it rises and loses gas and heat, it shrinks. It is essential to convert reservoir volumes into surface production. Enter the volumes at reservoir and surface conditions.
Hydraulic Retention Time (HRT)
Calculate the hydraulic retention time (HRT) of a reactor or tank, HRT = volume ÷ flow, dividing the working volume (m³) by the influent flow (m³/h). The result, in hours, is the average time the liquid stays in the unit and is decisive in designing clarifiers, anaerobic reactors, lagoons and aeration tanks: short times prevent reactions or settling from completing, while long times raise cost and footprint. Enter the working volume and the inlet flow.
Cistern Volume in Liters
Calculates capacity in liters of a rectangular cistern from its dimensions.
Compressed Air Receiver Volume
Sizes a compressed air receiver from the maximum number of motor starts per hour the compressor allows: V = 15 × free air delivery in m³/min × atmospheric pressure in bar ÷ (starts per hour × load-unload pressure band in bar). The constant 15 comes from the worst case, in which demand is exactly half the compressor capacity: the receiver then fills and drains at half flow, each of the two legs lasts twice what it would at full flow, and the whole cycle is four times that unit time — the condition that maximizes the number of starts, and the 15 is the 60 minutes in an hour divided by that 4. The result, in cubic metres, is the minimum volume: a smaller receiver makes the motor start more often than the manufacturer allows and overheats the winding, while a larger one costs nothing but money and floor space. Because volume is inversely proportional to the pressure band, widening the unload differential from 1 to 2 bar halves the tank, which is usually cheaper than buying a bigger vessel. Enter the compressor free air delivery, the maximum number of starts per hour, the load-unload pressure band and the local atmospheric pressure.
Sealed Subwoofer Box Volume Calculator
Computes optimal sealed subwoofer box volume via Vb = Vas / (Qtc^2/Qts^2 - 1) from speaker Thiele Small parameters.
The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.