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Water & constant-flow inventory

Tank Fill & Drain Time Calculator

Calculate ideal inventory-change time from simultaneous constant inflow and outflow.

179 / TANK FILL & DRAIN TIME

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Starting values are illustrative. Use your own costs, rates and assumptions.

INPUT GROUP 01

Entered assumptions and matching units

Check the assumptions before acting on a result.

Read the method and example

YOUR CALCULATION

Calculate ideal time for a constant-flow inventory change.

Inflow less outflow (m³/h)

6

Target less starting inventory (m³)

60

Ideal time to target

10 hr

Working capacity above the target (m³)

20

Keep the calculation

Saving is optional and stays on this device. Unsaved edits are not kept when you leave. CSV includes every input and the current results.

Illustrative inputs loaded. Replace them with your own assumptions.

How the tank fill & drain time calculator works

Net flow is inflow less outflow, while inventory change is target less start. If their directions agree, ideal time is inventory change divided by net flow. An already reached target takes zero time.

A different target cannot be reached by zero or oppositely directed net flow under these assumptions. Starting and target inventory must both fit the entered working capacity.

This is a linear inventory balance at constant measured flows, not gravity-orifice draining, pump selection, surge or overflow protection, tank design, operating control or a safety assessment.

Worked example

Moving from 20 to 80 m³ at 10 m³/h inflow and 4 m³/h outflow gives 6 m³/h net flow and 10 hours. A 50-m³ target instead takes five hours.

Sources and assumptions

The source material explains the underlying calculation or pricing structure. Entered prices, costs, schedules and scenario choices are your assumptions; this tool does not obtain supplier quotes or predict actual results.

  • Pipe Pressure-Drop Scenario

    Convert diameter to metres and flow to m³/s.

  • Reynolds Number

    Dynamic-property mode uses Re = density × velocity × characteristic length ÷ dynamic viscosity.

  • Pipe Flow Velocity

    Calculate pipe velocity from flow rate and actual internal diameter. Enter L/s, L/min, m³/h or U.S. gpm with mm or inches, and see mean velocity in m/s and ft/s.

  • Liquid Mass & Volume

    Estimate liquid mass from volume, or volume from mass, using your entered density. See liters, cubic meters, kilograms, tonnes and pounds together.

Calculation methods, testing and sources · Practical calculation guides