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RO Membrane Area Calculator

Work out ro membrane area instantly with clear inputs, formula shown and shareable results.

About RO Membrane Area Calculator

Membrane area is permeate flow divided by design flux. Flux is limited by fouling potential: 12-18 L/m2/h for surface water, 18-27 for brackish groundwater and up to 35 for high-quality feed. Elements are grouped into pressure vessels holding six or seven, and vessels into stages.

Formulas

Membrane area

Area (m2) = permeate flow (m3/h) x 1000 / flux (L/m2/h)

Element count

Elements = ceil(area / area per element); vessels = ceil(elements / elements per vessel)

Worked example

With the default values below, RO Membrane Area Calculator returns Membrane Elements Required of 113. Change any input above and every figure here is recalculated in your browser.

Inputs used

Required Permeate Flowminimum 0 m3/h
75 m3/h
Design Fluxminimum 0 L/m2/h
18 L/m2/h
Area Per Elementminimum 0 m2
37 m2
Elements Per Pressure Vesselminimum 1
6

Results

Membrane Elements Required
113
Membrane Area Required
4,166.67
Pressure Vessels Required
19
Actual Flux At Installed Area
17.9383

Step by step

  1. 1Values used
  2. 2Membrane area
  3. 3Element count
  4. 4Membrane Elements Required= 113
  5. 5Membrane Area Required= 4,166.67
  6. 6Pressure Vessels Required= 19
  7. 7Actual Flux At Installed Area= 17.9383

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why keep flux low on surface water?

High flux accelerates concentration polarisation and fouling, raising cleaning frequency and shortening membrane life. Design flux must reflect the feed's silt density index and organic content.

What is a staged array?

Concentrate from the first stage feeds a smaller second stage, typically in a 2:1 ratio, which raises overall recovery while keeping flux and crossflow velocity within limits in each stage.

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