---
title: "Water Treatment Calculators: RO, Softener, Filter Sizing, SDI | Filtsap"
description: "Free calculators for RO plant sizing, water softener resin and salt, sand and carbon filter vessels, cartridge filter housings, SDI and water unit conversion."
source: https://www.filtsap.com/tools/
updated: 2026-10-23
---

# Water treatment calculators

Free tools engineers and plant owners use every day: size an RO plant, a softener, a sand or carbon filter and a cartridge filter, work out SDI, and convert flow, TDS and hardness units. Every result can be sent to us for a checked quotation.

### [RO plant calculator](https://www.filtsap.com/tools/ro-plant-calculator/)

Free RO plant calculator: enter permeate flow, feed TDS and recovery to get feed and reject flow, number of 4" or 8" membranes, pressure vessels, permeate and reject TDS.

### [Water softener sizing calculator](https://www.filtsap.com/tools/water-softener-calculator/)

Size an industrial or residential water softener: enter hardness and daily water use to get resin volume, FRP vessel size and salt per regeneration.

### [Pressure sand and carbon filter sizing](https://www.filtsap.com/tools/pressure-filter-sizing-calculator/)

Size a pressure sand filter (PSF), multimedia filter (MMF) or activated carbon filter (ACF): enter flow to get filter area, FRP vessel size, media volume and backwash flow.

### [Cartridge filter housing sizing](https://www.filtsap.com/tools/cartridge-filter-sizing-calculator/)

How many filter cartridges and what housing size do you need? Enter flow and micron rating to get the number of 10, 20, 30 or 40 inch cartridges and the housing configuration.

### [SDI calculator](https://www.filtsap.com/tools/sdi-calculator/)

Free SDI calculator: enter t0, t15 (or t5, t10) from your SDI test to get SDI, percent plugging and whether your RO feed water is acceptable.

### [Water treatment unit converter](https://www.filtsap.com/tools/water-unit-converter/)

Convert LPH, LPM, m³/hr, KLD, GPD and GPM; TDS (ppm) and conductivity (µS/cm); and hardness in ppm CaCO₃, grains per gallon, °dH and °fH.

## Need filters, spares or a new plant?

Send the details on WhatsApp or through the form. An engineer reads every enquiry before we quote.

[Get a quote](https://www.filtsap.com/get-quote/) [WhatsApp](https://wa.me/918160852169?text=Hello%20Filtsap%2C%20I%20need%20a%20quote.)