Pool Filter Sand Calculator
The number is already stamped on the side of your tank. A sand filter holds a fixed charge, not a depth you measure, so the arithmetic was never the hard part. But labels fade. Then you are standing in the aisle at the pool store, guessing. That is what the pool filter sand calculator below is for: tank size in, pounds and bags out, with the spare bag already counted.
Your result
What to order
4 bags of #20 silica sand at 50 lb each, 200 lb total, for a 21 inch filter
That comes out at whole bags with nothing left over, which is tidier than it sounds risky. Pick up one spare anyway. Losing half a bag over the side of the tank turns the job into a second trip to the store.
- Fill to the line, not to the top
- The charge fills the tank about two thirds of the way up and stops. The empty space above it is freeboard, and the sand needs it to lift and tumble during a backwash. Pack the tank full and backwash stops cleaning anything.
- What the job costs in total
- $60 in media at $15 a bag. Doing it yourself, that is the whole bill. Handing it to a pool service adds roughly $150 to $300 in labour, since most of the time goes on digging the old sand out by hand.
- How this is worked out
- 21" tank = 200 lb sand × 1 = 200 lb ÷ 50 lb a bag = 4 bags
What is pool filter sand?
Graded silica, washed and screened so every grain falls in a narrow size band, around 0.45 to 0.55 mm. That band is the whole product. Sand from a builders merchant has grains of every size mixed together, and that mixture is what makes it useless here.
Here is the part that surprises people. The sand does not work like a sieve. The gaps between the grains are far bigger than the dirt being caught, so anything small enough to worry about should sail straight through. What actually happens is that particles bump into the grains on the way past and stick to them. Filtering is a surface effect, not a strainer.
Which explains why sand wears out while still being entirely present. Years of water rushing past rounds the sharp edges off and polishes the surfaces smooth, and smooth grains hold on to nothing. The tank is still full. It has simply stopped catching anything, and no amount of backwashing brings that back.
How much pool filter sand do you need
How much does yours take? Find the diameter of the tank and the answer follows. Every filter is built around a fixed volume of media, and the maker sets that charge in pounds. A 21 inch tank is about the most common on a home pool. It holds 200 lb, which is 4 bags.
| Tank | Sand | 50 lb bags | Published range | Typical models |
|---|---|---|---|---|
| 14" | 50 lb | 1 | 50 lb | Hayward S144T |
| 16" | 100 lb | 2 | 100 lb | Hayward S166T |
| 18" | 150 lb | 3 | 150 lb | Hayward S180T |
| 21" | 200 lb | 4 | 175 to 200 lb | Hayward S210T at 200, Pentair Tagelus TA50D at 175 |
| 24" | 300 lb | 6 | 275 to 300 lb | Hayward S244T at 300, Pentair Tagelus TA60D at 275 |
| 27" | 350 lb | 7 | 350 lb | Hayward S270T |
| 30" | 500 lb | 10 | 450 to 500 lb | Hayward S310T at 500, Pentair Tagelus TA100D at 450 |
The range column is there for a reason. Two makers can build a 21 inch tank and spec it differently. The internal shape differs, and so does the height of the laterals. So treat the middle column as a good guess. The plate on your own filter is the truth.
No label left at all? Measure across the widest part of the tank body, ignoring the valve on top and the base underneath. That gets you close enough to pick the right row. A filter is forgiving of a few pounds either way.
How to replace sand in a pool filter
It is a straightforward job. But it goes wrong in one specific place, so the order you do things in matters more than the skill does.
Shut the pump off at the breaker and set the valve to closed. Pull the drain plug at the bottom and let it empty, which takes longer than you expect. Take the valve off the top, and now you can see the standpipe running down the middle.
Tape over the top of that standpipe before you touch anything else. If sand gets down it, the sand goes into your pool rather than being filtered by it, and you will be vacuuming for a week.
Scoop the old sand out. A plastic cup works, a wet vac works better, and neither is quick. Then half fill the tank with water before the new sand goes in. The laterals at the bottom are brittle plastic fingers, and a bag of sand dropped onto a dry one snaps it. Water cushions the fall.
Pour the new media in slowly, keeping the standpipe centred. Fill to the level the maker marks, not to the brim. Rinse the tape off, refit the valve, then backwash for two minutes and rinse for one before you send any water back to the pool. That first backwash carries off the fine dust that comes in every bag.
How often to change pool filter sand?
Every 3 to 5 years on a normal home pool. That is a wide window because it depends far more on how hard the filter has worked than on how long it has been sitting there.
A pool that gets swum in daily through a long season, with sunscreen and oils going into the water, coats its sand quickly. A quiet pool under a cover for half the year can go the full 5 and a bit beyond. Neither is unusual.
The pressure gauge tells you more than the calendar does. Note what it reads just after a backwash while the sand is new. That is your clean baseline. Now watch it over the seasons. When the gauge climbs back to its high reading within days of a backwash, the water has cut channels through the bed. It is running past the sand rather than through it. That is the moment, whatever year it happens to be.
The other signal is water that stays cloudy while the chemistry tests perfectly. That one is more annoying. Most people don’t suspect the filter at all, and spend weeks throwing chemicals at it instead.
How many bags of pool filter sand in a yard
About 54 bags, since a cubic yard of dry graded silica weighs roughly 2,700 lb and the bags are 50 lb each.
Now the useful bit: you are never going to buy one. The biggest tank in the chart above, at 30 inches, holds 500 lb. That is under a fifth of a cubic yard. Even a filter twice that size stays well inside a single yard, so pool sand is a bagged product and bulk pricing never enters into it.
The figure is still worth knowing, because it puts the weight in perspective. Say you have a 21 inch filter. That is 4 bags, 200 lb, to be carried from the car to the equipment pad. Usually in one trip, because nobody wants to make two.
What pool filter sand costs
Between $10 and $25 a 50 lb bag, with most stores landing near $15. For a 21 inch filter at 4 bags, that is about $60 of sand.
| Media | Weight needed | Bags | Rough cost |
|---|---|---|---|
| #20 silica sand | 200 lb | 4 | $60 |
| Recycled glass media | 160 lb | 4 | $160 |
| Zeolite (ZeoSand) | 100 lb | 2 | $60 |
Read that table twice, because a weight saving is not always a bag saving. Both alternatives are lighter than sand for the same volume: recycled glass media fills the tank at 0.8 times the weight, zeolite (zeosand) at 0.5 times.
But bags only come whole. Glass needs 160 lb here against sand’s 200, and that still rounds up to 4 bags, so the premium lands on every one of them. Zeolite is the one that genuinely drops the count, to 2. Whichever you pick, match the volume and not the weight on the sand label, or you will badly overfill the tank.
Then there is the labour question. Doing it yourself, the bags are the entire bill. Calling a pool service adds $150 to $300, and that is not a markup on parts. It is an hour or two of somebody kneeling over a tank, scooping wet sand into a bucket. And honestly, that is the worst part of the whole job.
How to use this pool filter sand calculator
Start by telling it how you know your filter. If the label is readable, pick the second option and type the charge straight in, because that number beats every chart. If it has gone, measure the tank and use the diameter list.
Which media? Leave it on sand unless you are deliberately switching. If you are, watch what happens: the pounds drop while the tank stays just as full. Most people assume a lighter number means a smaller order. It does not.
Set the bag size to match what you are buying. Almost everything sold as pool filter sand comes in 50 lb bags. Glass and zeolite often do not. A bag size left wrong throws the count out straight away.
The price box is optional and it only covers media. Add your own labour figure on top if you are getting somebody in, because that side of the bill is usually the bigger one.
One habit worth picking up while you are here. Write the charge on the tank with a marker once you have worked it out. Think about where you will be in 3 to 5 years: in front of the same filter, asking the same question, with a printed label even less readable than it is today.
Pool filter sand questions
How much sand for a pool filter?
It depends on the tank, not the pool. A 16 inch tank takes about 100 lb, a 21 inch takes 200 lb, and a 30 inch takes 500 lb. Measure across the widest part of the tank if the label has worn off, then match it to the chart above.
How much sand goes in a pool filter?
Enough to fill it about two thirds of the way up, and no further. The gap left above the sand is called freeboard, and the sand needs that room to lift and churn when you backwash. Fill the tank to the top and backwashing stops working.
How often to change sand in a pool filter?
Every 3 to 5 years for a normal home pool. Heavy use shortens it. So does a pool that gets a lot of sunscreen and body oil in it, because that coats the grains faster than dirt alone would.
When to replace sand in a pool filter?
Watch the pressure rather than the calendar. If the gauge climbs back to its dirty reading within days of a backwash, the sand has channelled and water is running straight past it. Cloudy water that no amount of chemicals fixes is the other tell.
How to replace sand in a pool filter?
Pump off, valve to closed, drain plug out. Scoop the old sand out by hand or with a wet vac. Tape over the standpipe so nothing drops down it. Half fill the tank with water first, which cushions the laterals. Then pour the new sand in and backwash before you send water to the pool.
How much does it cost to replace sand in a pool filter?
The sand itself is $50 to $120 for most home filters. A pool service adds $150 to $300 on top. Nearly all of that is labour, because digging wet sand out of a tank by hand takes a while.
Can you use play sand in a pool filter?
No. Play sand is far too fine and it is not graded, so some of it washes straight through the laterals and back into the pool. The rest packs down tight and blocks flow. Filter sand is a specific grade, and the bag says so.
How many bags of sand for a pool filter?
Divide the charge by 50, then round up. A 21 inch filter needs 200 lb, so that is 4 bags exactly. Buy one more than the sum says anyway. Some always goes over the side while you pour, and being half a bag short means a second trip.