How to Tell What Size Pool Filter You Need in AZ

It is very common for homes in Arizona to have swimming pools. It doesn't matter if it's an in-ground pool or an above ground pool, a filter is a necessity. Pool filters are used to keep the pool water clean on a regular basis, and choosing the wrong size can lead to cloudy water, system strain, and costly repairs.

There are several factors pool owners should consider when selecting a pool filter size in Arizona. There are also common sizing mistakes to avoid, and owners should understand why the right filter is essential for maintaining a healthy pool environment.

Keep reading to find out how to tell what size pool filter you need in AZ.

Why Filter Size Matters in Arizona

The size of the pool filter directly impacts how efficient it is, how long it will last, and how good it is at maintaining clean water. If the filter is too small for the pool size, it will clog, work harder than it should be, and eventually, the equipment will fail. If the filter is too large, it will be more expensive and take up more space, but it will also oftentimes be more efficient and require less care.

In Arizona—particularly in cities like Tucson—filter sizing is even more critical due to:

• Dust, dirt, and pollen from desert air

• Frequent use in hot weather

• Water level dropping quickly

• Year-round pool operation

• Mineral-heavy hard water

• Pet and wildlife debris in outdoor pools

Choosing the correct size pool filter is not just a technical calculation—it’s also about understanding local conditions and usage habits. This can be the difference in minor vs major pool filter problems in AZ.

Key Factors That Determine Pool Filter Size

When deciding what size sand filter, what size cartridge filter, or what size DE filter is needed, there are a few things to keep in mind:

1. Pool Volume (in Gallons)

The most important factor in filter sizing is the total volume of water in the pool. This determines the amount of water that must be filtered regularly.

To estimate the pool’s volume, pool owners must consider the pool shape and then calculate the volume:

• Rectangular Pool: Length × Width × Average Depth × 7.5 = Gallons

• Round Pool: Diameter × Diameter × Average Depth × 5.9 = Gallons

• Oval Pool: Length × Width × Average Depth × 6.7 = Gallons

Even if the pool has a deep end, most experts recommend doing an average, as that will still consider the most shallow and deepest areas.

2. Flow Rate (Gallons Per Minute or GPM)

The flow rate capacity of a filter measures how quickly the pool pump can move water through the filtration system. It's typically expressed in gallons per minute (GPM).

It's best to turn over the entire pool volume every 8 hours. To determine this, divide the total gallons in the pool by 8, then by 60 (minutes) to find the required GPM.

Example: A 20,000-gallon pool20,000 ÷ 8 = 2,500 gallons/hour2,500 ÷ 60 = approximately 42 GPM

This is the minimum that should be considered, as the filter must be rated to handle this flow rate without resistance.

3. Pump Size and Horsepower

The pool pump must work together with the filter to ensure the water is filtered correctly. A powerful pump paired with a small filter can create too much pressure, while a weak pump with a large filter may not push enough water through efficiently.

A small size pump should be paired with a smaller filter, if appropriate, and a large size pump should be paired with a larger filter, if appropriate. These should not be mixed up.

4. Type of Pool Filter

Different types of filters handle water flow and debris differently. This affects sizing requirements.

• Sand filters: These require a larger surface area to handle finer debris.

• Cartridge filters: These require less water pressure and offer better filtration per square inch.

• DE filters: These offer the finest filtration, but need proper flow rate to avoid clogging.

Sizing Guidelines by Filter Type

1. Sand Filters

• Least precise filtration (~20–40 microns)

• Larger physical size needed to process more water

• This filter media is ideal for larger pools with light-to-moderate debris

Recommended Size:

• Up to 15,000 gallons: 21–24” diameter

• 15,000–25,000 gallons: 24–27” diameter

• Over 25,000 gallons: 30”+ diameter

2. Cartridge Filters

• Finer filtration (10–20 microns)

• Require less space and no backwashing

• Common in AZ due to water conservation concerns

Recommended Size:

• Minimum 100 square feet of surface area per 10,000 gallons

• For 20,000-gallon pool: 200–300 sq ft cartridge

3. Diatomaceous Earth (DE) Filters

• Finest filtration (~2–5 microns)

• Requires backwashing and recharging with DE powder

• Best for luxury pools or pools with high bather loads

Recommended Size:

• 1 sq ft of filter area per 10 GPM

• For 42 GPM flow rate: ~4.2 sq ft DE filter

Signs the Pool Filter Size Is Wrong

If, by chance, a pool owner gets a new filter that is the wrong size, there are some signs:

Too Small Filter:

• Frequent clogging or pressure spikes on the pressure gauge

• Poor water clarity

• Short filter lifespan

• Increased maintenance

Too Large Filter:

• Higher upfront cost

• Space limitations

• Inefficient use of smaller pumps

In most cases, having a filter that is too large is much better than having a filter that is too small, as it is more efficient at removing fine dust and sand that increases the total amount of debris.

Unique Sizing Considerations for Arizona Pools

The climate in Arizona gives pool owners some specific challenges that can influence filter size.

1. Dust and Pollen

Fine debris, like sand and dust, from monsoon storms and desert winds clog filters quickly. It might be best to buy a filter that is a bit larger than necessary to tackle these particles.

2. Frequent Use

A longer swim season mean filters must work harder and longer, requiring more surface area to prevent constant cleaning and excessive pool care.

3. Water Quality

Arizona water is often high in calcium and minerals. This contributes to scaling inside of filters and requires stronger filtration systems.

4. Wildlife and Pets

Backyard pools in Arizona may attract birds, insects, and even desert critters. This adds organic material to the water that smaller filters can’t always handle effectively.

Professional Sizing Services in Tucson, AZ

For homeowners who are unsure of what size pool filter they need, a professional Tucson pool cleaning and maintenance company can help. They can look at things like:

• Exact pool volume and turnover requirements

• Pump compatibility

• Filter type suitability

• Local water and debris conditions

• Space and plumbing considerations

Custom recommendations ensure that the filtering system is energy-efficient, environmentally conscious, and effective year-round.

Contact E-Konomy Pool Service & Supplies for New Filters

Proper pool filter sizing is extremely important for Arizona homeowners who are looking for clean, safe, and hassle-free pool water. Working with a local pool professional like E-Konomy Pool Service & Supplies helps ensure the right system is selected the first time—saving time, water, and money. Tucson pool owners can reach out to learn more.