Rectangular Tank and Sump Volume Calculator
Calculate the volume of a rectangular tank, pit or sump at any level, including tapered sumps whose plan area grows with height, and get litres per centimetre for level scaling.
- Prismoidal formula: V = h ÷ 6 × (Abottom + 4Amid + Alevel)
- A at level = 3 × 2 m
- V = 10.8 m³
Rectangular and Tapered Volume
Tapered sides (prismoidal formula): V = h ÷ 6 × (A1 + 4Am + A2)
A1 is the bottom area, A2 the area at the liquid level and Am the area at mid height. The prismoidal formula is exact for straight tapered sides. Litres per cm is the volume of a 1 cm slice at the present level, useful for level transmitter scaling and pump calculations.
Worked example
A 3 m × 2 m straight sided sump with 1.8 m of liquid holds 10.8 m³ (60 L per cm). If the top flares to 4 m × 3 m at 2.5 m depth, the same level holds about 14.4 m³.
Frequently Asked Questions
How do I calculate the volume of a rectangular tank?
Multiply length by width by liquid depth. All in metres gives cubic metres; multiply by 1000 for litres.
What if the sides are sloped?
Use the prismoidal formula, which averages the bottom, middle and top areas with weights 1, 4 and 1.
What is litres per cm used for?
To scale a level signal to volume, size pump start and stop bands and convert level change rate to flow.
Learn more on the blog
Basics of level measurement
A practical, field focused guide on instrumentationblog.in that explains the theory behind this calculator and how engineers apply it on real plants.
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