Tank Volume Calculator
Pick a tank shape — vertical cylinder, horizontal cylinder, rectangular box or sphere — enter the dimensions in centimetres and get the total capacity. Add an optional liquid level to compute the current filled volume and percentage. Results are shown in litres, cubic metres and US gallons, useful for aquariums, fuel tanks, chemical totes, rain barrels and process vessels.
Enter positive dimensions in centimetres; level (if given) must be between 0 and the tank height.
Total capacity
—
—
Currently filled
—
—
Fill level
100%
Formula
V = π × r² × H (r = diameter ÷ 2)
Formula
V_cyl = π r² H; V_sphere = (4/3) π r³; horizontal cylinder at level h: V = L × (r² · arccos((r−h)/r) − (r−h)√(2rh − h²)).
- · Enter every dimension in centimetres (cm): 1 L = 1 000 cm³, 1 m³ = 1 000 L.
- · Vertical cylinder: level h is measured from the bottom; partial fill is simply π r² h.
- · Horizontal cylinder: partial volume uses the circular-segment area × length; a half-full tank (h = r) is exactly half the total capacity.
- · Rectangular: partial fill = length × width × h, the most intuitive case.
- · Sphere: with h measured from the bottom, partial fill = π h² (3r − h) / 3; h = r yields exactly half.
- · US gallon conversion uses 1 US gal = 3 785.411 784 cm³ (NIST SP 811); UK gallons (4 546.09 cm³) are not displayed.
- · Formulas: CRC Standard Mathematical Tables §4.6 / §4.8, Perry’s Chemical Engineers’ Handbook §10.
Frequently asked
For a horizontal cylinder, where is the liquid level measured from?
From the lowest point inside the tank up to the liquid surface; the maximum possible level equals the tank diameter. A 1 m-diameter horizontal cylinder filled to 0.5 m is exactly half full. The tool clamps levels above the diameter to "full" automatically.
Why are aquariums sized in gallons when the calculation gives litres?
The North-American aquarium trade has long sized tanks in US gallons, so "20-gallon long" or "55-gallon" remain industry shorthand. The tool shows both litres and US gallons (1 US gal ≈ 3.785 L), so a 90 × 45 × 45 cm rectangular tank reads as ≈ 182 L ≈ 48 US gal.
My tank is none of these four shapes — for example, it has elliptical ends. Now what?
This tool covers the four most common geometries. For elliptical cross-sections, dished or hemispherical ends, or composite shapes (cylinder + cone), split the volume into pieces or consult an engineering handbook — Perry’s Chemical Engineers’ Handbook §10 has the complete formula set. Industrial process tanks usually ship with a strapping/calibration table.
Why does my computed capacity differ from the rating on the tank label?
Two common reasons: (1) the label often quotes nominal capacity, which already subtracts the top few centimetres of ullage / vapour space to prevent overflow — that alone is typically 5–10 % low. (2) Wall thickness reduces the inside dimensions; this tool assumes you entered inside dimensions. If you measured outside, subtract twice the wall thickness from each linear dimension.
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