Tank Capacity Calculator

Current fill{{ resultsReady ? formatVolume(computation.values.current_volume_m3) : '—' }} Filled{{ resultsReady ? `${formatNumber(computation.values.fill_percent, 1)}%` : '—' }} Headspace{{ resultsReady ? formatVolume(computation.values.headspace_volume_m3) : '—' }}

Tank shape and orientation:

Orientation changes the depth-to-volume relationship even when full cylinder capacity is unchanged.

Head geometry:

The model adds two identical heads to the entered straight shell dimension.

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Internal height:

Use the clear inside height, excluding wall thickness.

Measured fill depth:

Measure from the lowest inside point. Maximum for the selected geometry: {{ maximumDepthDisplay }}.

Capacity display:

This display preference does not reinterpret any source measurement.

Planning reserve:

Neutral default: 0%. Verify actual operating and overfill limits separately.

Capacity analysis

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Geometry method:

Full precision feeds the summary, chart, dip table, and exports; rounding is display-only.

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This ideal-geometry estimate does not replace the exact tank’s certified strapping or calibration table, drawings, verified operating limits, alarms, thermal-expansion allowance, or overfill-prevention procedure.

The chart renderer is unavailable. The same depth values remain available in the dip table.

Depth from bottom	Volume	Shell fill	Copy
{{ row.depthDisplay }}	{{ row.volumeDisplay }}	{{ row.percentDisplay }}

Tank capacity is the volume enclosed by the inside surfaces, not the volume suggested by outside dimensions or a nominal product label. Wall thickness, linings, fittings, curved ends, internal obstructions, and the normal operating limit can all make the usable amount smaller than the shell's apparent size.

Shape controls both total capacity and the relationship between liquid depth and volume. A rectangular tank gains the same volume for every equal rise in depth because its horizontal area is constant. A horizontal cylinder gains volume slowly near the bottom, more quickly near its centerline, and slowly again near the top. A vertical cylinder has a constant shell area, but curved heads make the first and last depth increments nonlinear.

Orientation matters even when two cylinders share the same diameter and straight-shell length. Turning a cylinder from vertical to horizontal does not change its full geometric volume, but it changes how a dip measurement maps to liquid volume. A half-depth reading in a symmetric horizontal tank is half full; other depth fractions generally are not equal to the same volume fractions.

Straight shell: The cylindrical section between the heads, measured internally along its axis.
Head: A flat, hemispherical, or 2:1 ellipsoidal end attached to the straight shell.
Fill depth: Vertical liquid height measured from the lowest inside point.
Headspace: Geometric capacity above the current liquid level.
Planning reserve: A user-entered percentage withheld from geometric capacity for planning; it is not a certified safe-fill limit.

A depth-to-volume table is useful for stock checks and rough transfer planning, but ideal geometry cannot reproduce a real tank's tilt, deformation, deadwood, nozzles, roof or bottom shape, temperature effects, or installation-specific calibration. Commercial and regulated measurements should use the exact tank's certified strapping or calibration table.

Overfill prevention is a separate safety system. Normal fill limits, alarm levels, reaction time, thermal expansion, transfer rate, shutdown procedures, and regulatory requirements must come from engineering records and operating procedures. A geometric reserve does not authorize filling to a particular level.

How to Use This Tool:

Measure clear inside dimensions and identify the actual orientation and end geometry before using a depth reading.

Choose Tank shape and orientation. For a cylinder, select flat, hemispherical, or 2:1 ellipsoidal heads; the entered straight-shell length excludes both heads.
Enter the required inside dimensions with the unit beside each measurement. Use clear internal height for a rectangular tank and internal diameter for a cylinder.
Enter Measured fill depth from the lowest inside point. Correct the value if it exceeds the maximum shown for the selected geometry.
Select a capacity display unit and enter a planning reserve only if you have a defensible allowance. Review total capacity, current liquid, headspace, and the depth-to-volume profile against tank records.

Interpreting Results:

Tank capacity is the ideal full-shell volume. Current volume applies the measured depth to the selected geometry, and Headspace is capacity minus current volume. These are geometric quantities rather than certified inventory or safe operating limits.

Usable after entered reserve subtracts the chosen percentage from full capacity. A negative Remaining to entered allowance means the current modeled liquid volume is above that user-entered allowance; it does not by itself identify an alarm, spill, or regulatory condition.

Check diameter versus radius and confirm that the shell length excludes curved heads.
Do not convert depth percentage directly to volume percentage for a horizontal cylinder or a vertical tank with curved heads.
Use the same measurement datum as the tank's certified table when comparing a dip reading with operational records.

Technical Details:

All lengths are converted to meters before geometry is evaluated, and volume is first computed in cubic meters. Rectangular tanks use a prism. Cylindrical tanks combine a straight circular shell with two identical heads. A hemispherical head has an axial depth equal to the radius; a 2:1 ellipsoidal head has an axial depth equal to half the radius.

Formula Core:

For internal length L, width W, and height H, rectangular capacity is:

V_{rect} = L W H

For a cylinder with internal radius r, straight-shell length L, and single-head axial depth a, full capacity adds the shell and two half-ellipsoidal heads:

V_{full} = π r^{2} L + \frac{4}{3} π r^{2} a

Flat heads use a = 0. Hemispherical heads use a = r, and 2:1 ellipsoidal heads use a = 0.5r.

A horizontal cylinder uses the circular-segment area at liquid depth h:

A_{seg} = r^{2} \arccos (\frac{r - h}{r}) - (r - h) \sqrt{2 r h - h^{2}}

The horizontal partial volume is the segment area times straight-shell length plus the filled part of both heads:

V_{horizontal} = A_{seg} L + π a h^{2} (1 - \frac{h}{3 r})

That expression applies from empty through full depth, with the head contribution capped at the full two-head volume. A vertical tank is evaluated in three stages: the lower curved head, the constant-area straight shell, and the mirrored upper head. Flat-ended vertical tanks reduce to circular area times depth.

Reserve and fill rules:

The planning reserve changes the comparison limit, not the geometric capacity:

V_{usable} = V_{full} (1 - \frac{p}{100})

Fill percentage is current volume divided by full volume, multiplied by 100. The allowance status is within the entered allowance when current volume is less than or equal to usable capacity. Eleven depth points, from 0% through 100% of internal height in 10% steps, form the dip table.

Tank capacity display unit conversions from cubic meters
Display unit	One unit in cubic meters
Liter	0.001 m³
US gallon	0.003785412 m³
Imperial gallon	0.00454609 m³
Cubic foot	0.028316846592 m³

For a flat-ended horizontal cylinder 2 m in diameter and 5 m long, full capacity is about 15.708 m³. A 1 m depth reaches the centerline, so the current volume is about 7.854 m³, exactly 50% of the ideal capacity.

Full-precision geometry feeds all results. Rounding occurs only when values are displayed, so changing the display unit does not reinterpret or recalculate the entered measurements.

Limitations and Safety Notes:

Ideal geometry is suitable for estimation, not custody transfer, overfill authorization, or structural design.

Use certified tank drawings and calibration tables for actual inventory, especially when the tank is tilted, deformed, insulated, internally fitted, or not a perfect supported shape.
Temperature expansion, liquid density, foam, vapor space, roof displacement, sediment, piping, alarms, and transfer dynamics are not modeled.
Verify normal operating capacity, maximum working level, alarm set points, and shutdown procedures with the responsible engineer and applicable rules.

References:

NIST Guide to the SI, Appendix B.8 conversion factors, National Institute of Standards and Technology.
ISO 12917-1:2017, calibration of horizontal cylindrical tanks, International Organization for Standardization, 2017.
API Standard 2350, 5th Edition, Overfill Prevention for Storage Tanks in Petroleum Facilities, American Petroleum Institute.

Tank Capacity Calculator

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Capacity analysis

Geometry method:

How to Use This Tool:

Interpreting Results:

Technical Details:

Formula Core:

Reserve and fill rules:

Limitations and Safety Notes:

References: