Storage Tank Size & Level Calculator

Process Parameters

Tank Tag i

Roof Type i

Req. Working Vol m³

Density (ρ) kg/m³

Inflow Rate (Q_in) m³/h

Outflow Rate (Q_out) m³/h

Tank Geometry

Diameter (D) mm

Height (H) mm

Low Level Settings (LLLL)

Pumpout Nozzle inch

Nozzle Type i

LLLL Mode i

LLLL Override mm

Level Spacing & Holdup

LLL Holdup Time min

HLL Holdup Time min

NLL % (of Working Span) i

High Level Constraints (HHLL)

Overflow? i

Overflow Size inch

Valve Closure Time min

Min Density kg/m³

Analysis Results

Tank Area (A)	- m²
Pumpout Velocity i	- m/s
Overflow Froude No. i	-

Elevation Profile (from Bottom)

Tank Top (Reference)	- mm
HHLL (High-High)	- mm
HLL (High)	- mm
NLL (Normal)	- mm
LLL (Low)	- mm
LLLL (Low-Low)	- mm

Volumetric Checks

Total Geom. Volume	- m³
Working Volume i	- m³
Dead Volume (< LLLL)	- m³
H/D Ratio i	-
Capacity Utilization i	- %
Roof Velocity i	- m/h

Actions

Visual Layout

Scaled visualization of levels

H: - mm

HHLL High-High (Trip)

HLL High (Alarm)

NLL Normal

LLL Low (Alarm)

LLLL Low-Low (Trip/Pump Protection)

Technical Notes & Engineering Logic

Variable Definitions

LLLL (Low-Low Liquid Level): Minimum level to prevent pump vortexing/cavitation. Based on API 650 nozzle height + 150mm buffer.
HHLL (High-High Liquid Level): Maximum safe fill level. Calculated top-down from shell height, accounting for overflow gap, thermal expansion, and valve closure inflow.
Working Volume: The usable volume between HLL and LLL.

Formulas

Tank Cross‑Sectional Area: A = (π·D²)/4
Volume at Liquid Height h: V = A·h = (π·D²/4)·h
Holdup Height for a Flow & Time: Δh = (Q·t)/A
Use consistent units: Q in m³/h (or m³/min), t in h (or min), A in m² ⇒ Δh in m.
Overflow Froude Number: Fr = v / √(g·D_ov), where v = Q/A_ov.
Practical self‑venting overflow guidance often targets Fr < 0.3 (verify with project / licensor practice).
Thermal Expansion Headspace (density proxy): V_thermal = V·(ρ_max/ρ_min − 1), then h_thermal = V_thermal/A.

Assumptions

Tank is vertical, cylindrical, and flat-bottomed.
Inflow/Outflow rates are constant max values for sizing checks.
"Floating Roof" disables overflow gap logic (assumes roof seals/vents handle limits) and adds velocity check.

Standards & References

API 650 – Welded Tanks for Oil Storage (nozzle minimum opening heights table used for pump‑out nozzle geometry).
API 2000 – Venting Atmospheric and Low‑Pressure Storage Tanks (venting/overfill protection philosophy; confirm project requirements).
Project / Client Standards – Level alarm/trip margins, holdup times, and overflow criteria.

Tank Size Calculator