Sizing Your Pool Filter: A Complete Guide & Calculator

Dreaming of crystal-clear blue water in your pool during Australian summer?  Your pool filter system is key to achieving that pristine clarity, and as the pool owner, you're in charge of choosing the right filter and pump combo. With so many filter types and sizes, selection can feel daunting. This guide simplifies pool filter sizing, ensuring sparkling water all season long. We'll break down filter types and provide a step-by-step method to find your perfect match.

For a quick response, utilize our convenient calculator below:

Pool Filter Sizing Calculator

Find the right pool filter size based on your pool dimensions, type, and desired turnover rate.

Rectangular
Round
Oval

Pool DimensionsLength (meters)Width (meters)Average Depth (meters)Diameter (meters)Average Depth (meters)Length (meters)Width (meters)Average Depth (meters)

Pool ParametersPreferred Filter Type-- Select Filter Type --Sand FilterCartridge FilterDE FilterDesired Turnover Rate (times per day)1 time per day1.5 times per day2 times per day2.5 times per day3 times per dayNote: For Australian pools, 1.5-2 turnovers per day is typically recommended. Consider a higher turnover rate for pools with heavy usage, high debris load, or in areas with intense sunlight. Calculate Filter Size

Your Results

Pool Volume: -- Litres

Required Flow Rate: -- LPM

Recommended Filter Size:

Sand Filter: --

Tank Diameter: --

Sand Capacity: --

Cartridge Filter: --

Surface Area: -- square feet

DE Filter: --

Grid Area: -- square feet

Important: Always consult manufacturer specifications for the exact model you're considering. These recommendations are general guidelines and may vary by manufacturer.
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Confused by the calculator?  Read on to learn what information you'll need:

Table of Contents

• Swimming Pool Filter Types
• Step-By-Step: How to Size the Pool Filter
• Example: What Size Sand Filter for a 50,000 Litre Pool?
• Key Takeaway

Swimming Pool Filter Types

What type of pool filter is most effective? DE filters are most effective for clearest water but are costly. Sand filters are economical and easy. Cartridge filters offer a balance. How long do pool filters last? It varies. While the filter units last for many years, the filter media inside requires periodic replacement: sand in sand filters every 5-7 years, cartridges in cartridge filters every 2-3 years, and DE powder is replenished during backwashing for DE filters, with the grids lasting for many years.

Step-By-Step: How to Size the Pool Filter

Step 1: Calculate Your Pool Volume

Your pool's volume is the starting point for all sizing. Use these formulas to calculate yours accurately: (π = 3.14)

• Rectangular Pool: Length (m) x Width (m) x Average Depth (m) x 1000 = Volume (Litres)
• Round Pool: π x Radius (m) x Radius (m) x Average Depth (m) x 1000 = Volume (Litres)
• Oval Pool: (Length (m) / 2) x (Width (m) / 2) x π x Average Depth (m) x 1000 = Volume (Litres)
• Freeform Pools: Estimate by breaking into several simple sections.

Step 2: Determine Your Ideal Turnover Rate

Decide how many times you want to circulate your pool water daily. For Aussie pools, 1.5 to 2 turnovers per 24 hours is a good range. Consider increasing turnover (closer to 2 or slightly more) for:

• Hot climates & intense sunlight (algae prevention)
• High debris load (eucalyptus leaves, dust, bushfire ash)
• Heavy pool usage

To further assist with heavy debris loads common in Australia, consider a robotic pool cleaner.  While your filtration system is essential for water circulation, a robotic cleaner effectively removes debris from the pool floor, walls, and water surface, improving clarity and reducing the need for excessively high turnover rates.

Step 3:  Calculate Your Required Pump Flow Rate (LPM)

Use this formula to find the minimum flow rate your pump needs to achieve your desired turnover:

Required Flow Rate (LPM) = Pool Volume (L) ÷ Turnover Time (minutes)

Remember: This formula gives you the basic flow rate assuming no delays from pipes. In reality, pipes can slow things down a bit, so pick a pump with a slightly higher flow rate to be safe.

Step 4: Choose Your Pool Filter Type - Sand, Cartridge, or DE

Select your filter type based on your needs and preferences (refer back to the "Swimming Pool Filter Types" section for a quick guide). Your filter type will influence the specific sizing in the next step.

Step 5: Size Your Filter to Match Your Pump & Pool

Crucially, your filter must handle your pump's flow rate. Select a filter with a maximum flow rate (GPM or LPM) equal to or greater than your calculated pump flow rate. Follow these guidelines for each filter type, considering both pool volume and pump flow:

Sand Filters

Sizing Metric: Tank diameter & sand capacity.

Guidelines:

• Small Pools (up to 40,000L): 16-18" tank (40-50kg sand)
• Medium Pools (40,000-60,000L): 22-24" tank (75-100kg sand)
• Large Pools (60,000L+): 28-32" tank (125-175kg sand)

Flow Rate Check: Ensure the filter handles 40-50 LPM per square foot of filter area.

Action: When choosing a sand filter, look for models within the recommended tank diameter range for your pool size and verify its flow rate capacity is sufficient for your pump.

Cartridge Filters

Sizing Metric: Total cartridge surface area.

Guidelines:

• Small Pools: 50-100 sq ft
• Medium Pools: 100-200 sq ft
• Large Pools: 200-400+ sq ft

Flow Rate Check: Aim for at least 1 sq ft of filter area per 3.8 LPM (1 GPM) of pump flow.

Action: Select a cartridge filter with a surface area within the recommended range for your pool size and ensure it meets the flow rate guideline based on your pump. Always prioritize manufacturer specs for the specific filter model.

DE Filters

Sizing Metric: Total DE grid area.

Guidelines:

• Small Pools: 24-36 sq ft
• Medium Pools: 36-48 sq ft
• Large Pools: 48-72+ sq ft

Flow Rate Check: DE filters typically handle 5.7-7.6 LPM per sq ft of filter area.

Action: Choose a DE filter with a grid area in the recommended range for your pool size and verify its flow rate capacity is suitable for your pump, using manufacturer specifications.

Step 6: Final Check - Manufacturer Guidelines

Consult Manufacturer Resources: Always refer to pump and filter manufacturers' sizing charts, tables, and online calculators. These are the most accurate and specific resources for your equipment selection.

Example: What Size Sand Filter for a 50,000 Litre Pool?

Let's quickly size a sand filter for a common 50,000 litre Aussie pool.

1. Pool Volume: 50,000 Litres (given)
2. Turnover Rate: Aim for 2 turnovers per day (good for Aussie climate)
3. Pump Flow Rate: Required Flow Rate = 50,000L ÷ 720 minutes (12-hour turnover) = 70 LPM (rounded up). You need a pump delivering at least 70 LPM (adjust for plumbing resistance).
4. Filter Type: Sand Filter (chosen for this example)
5. Sand Filter Size: Guideline for 50,000L pool: Medium Sand Filter (22-24" tank, 75-100kg sand). Flow Rate Check: 22-24" sand filters typically handle well over 70 LPM. Example: A 24-inch sand filter with a maximum flow rate of 120 LPM would be suitable.
6. Final Check: Always confirm the manufacturer's specs for your chosen filter model to ensure it meets your flow rate needs.

In short, for a 50,000 litre pool, a 22-24 inch sand filter tank size is a good starting point, but always verify the flow rate capacity of the specific filter model matches your pump.

Key Takeaway

• Pool Volume is First, Pump Flow is Next, Filter Size Connects Them: Know your pool volume, calculate pump flow for desired turnover, then size the filter to match the pump and volume.
• Pump GPM Dictates Minimum Filter Size: Never undersize your filter relative to your pump's flow rate.
• Filter Type Matters for Sizing: Sand, cartridge, and DE filters have different sizing metrics and flow rate capacities.
• Manufacturer Guidelines are Essential: Use manufacturer charts and recommendations for accurate, model-specific sizing.

By following these steps, you'll confidently choose the right pool filter size and enjoy a sparkling, healthy pool all Aussie summer!