To measure a sand filter, you need two key numbers: the tank diameter (measured across the widest point of the outer shell) and the filter area in square feet (listed on the data plate). These tell you the filter’s capacity, what replacement parts to order, and how much sand it holds. Whether you’re replacing an old filter, ordering new sand, or sizing a replacement, here’s how to get accurate measurements.
Check the Data Plate First
Every sand filter has a spec sticker or metal plate attached to the tank, usually near the top or on the side. This label lists the make, model number, serial number, and the available sizes for that product line, with your specific unit marked. It also typically shows the filter area in square feet, the design flow rate, and the maximum operating pressure. If this label is intact, it gives you everything you need without pulling out a tape measure.
Write down the model number and filter area. The filter area (measured in square feet) is the number that determines how much water your filter can process. For example, a Hayward Pro Series S244T has 3.14 square feet of filter area, while a smaller S166T has just 1.4 square feet. That single number drives everything else: sand capacity, compatible pump size, and the volume of pool water the filter can handle.
How to Measure the Tank Diameter
If the data plate is faded, damaged, or missing entirely, you’ll need to measure the tank yourself. Use a tape measure and stretch it across the widest point of the tank’s outer wall, from one side to the other. This gives you the outside diameter. Common residential sand filter diameters are 16, 19, 22, 24, 27, and 30 inches.
Keep in mind that the outside diameter includes the tank wall thickness, so it will be slightly larger than the internal diameter listed in spec sheets. For most fiberglass or polymer tanks, wall thickness is roughly a quarter inch on each side, meaning the outside measurement runs about half an inch wider than the nominal size. A filter sold as a “24-inch” model will measure close to 24.5 inches across the outside. If your tape reads 24 to 25 inches, you’re almost certainly looking at a 24-inch filter.
Also measure the height of the tank from the base to the top of the dome. This helps narrow things down when two models share the same diameter but differ in sand capacity and filter area.
Measuring Internal Components
If you’re replacing the lateral assembly, standpipe (center pipe), or other internals, you need measurements from inside the tank. Remove the multiport valve or top dome to access the interior. Lay a yardstick or straight edge across the opening and measure the inside diameter at the widest point. Then measure the depth from the top opening down to the bottom hub where the laterals connect.
For the standpipe specifically, measure its total length and the outer diameter of the pipe itself. Standpipes are not universal. A pipe that’s even half an inch too short will let unfiltered water bypass the sand bed, and one that’s too long won’t allow the valve to seat properly. The lateral arms radiating from the bottom hub also vary by model, so count them and measure from the hub center to the tip of one lateral to confirm the correct replacement set.
Matching Filter Size to Sand Capacity
Once you know your model or tank diameter, you can determine how much sand the filter needs. Sand capacity varies significantly between models, even among filters that look similar from the outside. Here are common examples:
- 1.4 sq ft filter area (Hayward S166T, Waterway FS01619, Sta-Rite Crystal Flo II): 100 lbs of sand
- 1.75–1.8 sq ft (Hayward S180T, Pentair Sand Dollar 40): 150 lbs of sand
- 2.3–2.6 sq ft (Sta-Rite Crystal Flo II, Waterway FS02225): 250 lbs of sand
- 3.14 sq ft (Hayward S244T, Pentair Triton II TR 60): 250–300 lbs of sand
- 3.5–3.7 sq ft (Hayward S270T, Sta-Rite Crystal Flo II): 350 lbs of sand
- 4.9–4.91 sq ft (Hayward S310T, Pentair Triton II TR 100): 450–500 lbs of sand
Some larger Pentair models, like the Triton II series, also require a layer of pea gravel beneath the sand. The TR 60 calls for 75 lbs of gravel under its 250 lbs of sand, while the TR 100 needs 150 lbs of gravel under 450 lbs of sand. Most Hayward, Sta-Rite, and Waterway filters skip the gravel entirely. Always confirm whether your specific model requires it before filling.
How Filter Area Relates to Flow Rate
The filter area in square feet isn’t just an abstract spec. It determines how many gallons per minute your filter can handle. Sand filters are designed to process water at a rate of 2 to 6 gallons per minute for every square foot of filter area, with most residential systems targeting the middle of that range.
A filter with 3.14 square feet of area, for instance, can handle roughly 6 to 19 GPM depending on how aggressively you push it. At a moderate rate of about 5 GPM per square foot, that filter processes around 15 GPM comfortably. This matters when you’re pairing a filter with a pump: if your pump pushes more water than the filter can handle, you get poor filtration and higher pressure. If you’re sizing a new filter, divide your pump’s GPM output by 5 to estimate the minimum filter area you need in square feet.
What to Do When the Label Is Gone
A missing data plate is common on older filters exposed to sun and pool chemicals for years. If measuring the tank doesn’t give you a confident match, try these approaches. Look for any remaining markings stamped into the tank itself, not just the sticker. Some manufacturers mold the model number into the plastic near the base or inside the tank collar.
You can also identify the filter by its valve connection size and configuration. Measure the pipe diameter going into the multiport valve (common sizes are 1.5 and 2 inches) and note whether the valve is top-mounted or side-mounted. Combine that with your tank diameter and height, and a pool supply store can usually narrow it down to one or two possible models. Taking a photo of the full filter with a tape measure visible across the top gives a store employee or online forum enough to work with.