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Process Design

Rectangular Tank Volume Calculator

Rectangular tanks, basins, sumps, and launders size by the simplest geometry of all — length × width × height — but the useful number in operation is the working volume at the liquid depth, together with the freeboard left above it. This calculator estimates the total geometric volume, the liquid (working) volume at the entered depth, the fill percentage, the freeboard height, and the ullage. It is a preliminary geometric estimate assuming a clean rectangular prism — not a calibrated strapping table and not a mechanical design.

TypeInteractive engineering calculator

Calculator

m
m
m
m
Result
Total geometric volume24 m³
Liquid / working volume18 m³
Fill percentage75 %
Freeboard height0.5 m
Empty volume (ullage)6 m³

Preliminary geometric estimate for a rectangular prism with vertical walls and a flat floor. Ignores wall thickness, internals, sloped floors, and dead volume. Not a calibrated strapping table or mechanical design.

Formulas

Total volume
V_total = L × W × H
Liquid volume
V_liquid = L × W × depth
Fill fraction
fill = depth / H
Freeboard
freeboard = H − depth
Ullage
ullage = V_total − V_liquid

Diagram

Rectangular tank: V = L × W × HL (length)W (width)HliquidfreeboardV = L × W × H

Worked example

A rectangular tank is 4.0 m long, 3.0 m wide, and 2.0 m high. The liquid depth is 1.5 m. What are the total and working volumes?

  1. 01V_total = L × W × H = 4.0 × 3.0 × 2.0 = 24.0 m³
  2. 02V_liquid = L × W × depth = 4.0 × 3.0 × 1.5 = 18.0 m³
  3. 03fill = depth / H = 1.5 / 2.0 = 75.0%
  4. 04freeboard = H − depth = 2.0 − 1.5 = 0.5 m
  5. 05ullage = V_total − V_liquid = 24.0 − 18.0 = 6.0 m³
Result

Total volume = 24.0 m³; liquid volume = 18.0 m³; fill = 75.0%; freeboard = 0.5 m; ullage = 6.0 m³.

FAQ

What is the difference between total and working volume?
Total volume is the full geometric capacity, L × W × H. Working (liquid) volume is what is actually held at the operating depth. The space left above the liquid is the freeboard, and the empty volume is the ullage. Tanks run with freeboard for surge, foam, and overflow protection, so working volume is normally less than total.
Does this account for sloped floors or sumps?
No. It assumes a flat floor and vertical walls. A sloped floor, hopper, or integral sump changes the volume near the bottom and is not included in this estimate.
Are the dimensions internal or external?
Use internal dimensions. This estimate is the internal liquid space and does not correct for wall thickness.
Can I use this as an inventory chart?
For a true rectangular prism the liquid volume is linear with depth, so a depth reading does give a volume — but this is still a preliminary estimate. For inventory or custody work use the verified drawings and any calibration data for the actual basin.

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