Above-Ground Pools
The 18-foot pool, and the three things that change with it
Going from 15 feet to 18 is not 20 percent more pool. It is nearly twice the water, and almost everything downstream of that scales with it.
Heads up: we earn a commission if you buy through the links on this page, at no extra cost to you. It never decides the ranking — here is how we pick and here is the full disclosure. Prices are checked automatically; last verified October 8, 2026.
Quick picks
Segmented before it is ranked — the right answer depends on which of these you actually are. Tap any row for the full write-up.
The pool at this size
At 18 feet the frame, the wall height and the filtration all step up together. This is the class the size implies, not an upscaled 15-footer.
| # | Product | Best for | Score | Price |
|---|---|---|---|---|
| 1 | Intex Ultra XTR Frame Pool Set, 18ft x 52in The biggest, sturdiest thing in this class that a homeowner can still put up in a weekend. It is also, by a wide margin, the most expensive one to run. | A family that will still be using it in year threeSeveral seasons | 8.4out of 10 |
What it ships with, and why
A sand filter rather than a cartridge is not an upsell at this volume. It is the manufacturer accepting that cartridges stop being economic here.
| # | Product | Best for | Score | Price |
|---|---|---|---|---|
| 1 |  Intex Krystal Clear Sand Filter Pump Sand filtration replaces a recurring cartridge purchase with a backwash valve and a bag of sand that lasts years. On a pool you intend to keep, the arithmetic favors it. | Getting off the cartridge treadmillSeveral seasons | 8.4out of 10 |
Buy on day one, not in July
Ground cloth and a solar cover are both proportionally more valuable at this size, because both scale with area.
| # | Product | Best for | Score | Price |
|---|---|---|---|---|
| 1 | No image Pool Ground Cloth / Under-Pool Pad Most liner punctures come from underneath, from a stone or a root you did not see. A ground cloth is the cheapest way to avoid the most expensive repair in above-ground pool ownership. | Protecting the liner from belowSeveral seasons | 8.5out of 10 | |
| 2 |  Bubble Solar Cover for Above-Ground Pools It cuts evaporation, and evaporation is simultaneously your water bill, your chemical bill and your heat loss. Nothing else on this site reduces three costs at once. | The single highest-return accessory hereSeveral seasons | 9.0out of 10 |
The short version
- It is not a 20 percent step, it is a 76 percent one. A 15-foot Steel Pro MAX holds 3,955 gallons; an 18-foot Ultra XTR holds 6,981.
- Level ground gets harder, not just bigger. The tolerance stays the same while the area you have to hold it across nearly doubles.
- Sand filtration arrives here for a reason. The cartridge treadmill stops being economic at this volume.
- Every running cost scales with the water — chemicals, filling, heating and pump hours all move together.
The number that explains this whole page
What 15 feet to 18 feet actually means
6,981 − 3,955 = 3,026 gal 3,026 ÷ 3,955 = 0.765
76 percent more water for 20 percent more diameter
Every argument on this page follows from that figure. More water is more chemicals, more filling, more heating, more pump hours and more ground to keep level — and none of it is a criticism. It is simply the honest description of what you are buying, and the category tends to sell the diameter rather than the volume.
What changes: ground
Above-ground pools want ground level to within about an inch across the whole footprint, and that tolerance does not relax as the pool gets bigger. At 18 feet you are holding the same tolerance across a footprint of roughly 254 square feet rather than 177.
This is the failure that ends large above-ground pools, and it ends them structurally rather than cosmetically. Water finds the low side, the wall on that side carries load it was not designed for, and the failure is sudden. Our leveling guide covers the method, and our surface guide covers what you can and cannot put a pool this size on.
What changes: filtration
Intex rates the C1000 cartridge pump for pools up to roughly 6,000 gallons, and an 18-foot Ultra XTR is 6,981. That is not a marketing boundary, it is the point at which the arithmetic runs out, and it is why the manufacturer ships this pool with a 2,100 GPH sand filter instead.
The practical difference is what the recurring cost is made of. A cartridge pool buys cartridges — eight or nine a season on heavy use, as our cartridge roundup works out. A sand pool backwashes instead, so the consumable becomes water and electricity and the media lasts several seasons. Our sand versus cartridge comparison is the full version of that decision, and 18 feet is where it stops being close.
What changes: the season bill
| Line | How it scales | Where it is priced |
|---|---|---|
| Filling | Directly with gallons | Cost to fill guide |
| Chemicals | Directly with gallons | Chemical cost guide |
| Pump hours | With gallons ÷ flow rate | Run-time guide |
| Heating | With volume and surface area | Heating cost guide |
| Evaporation | With surface area | Solar cover payback guide |
| Filter media | Changes category entirely | Sand versus cartridge |
Filling is the one people feel first. At the EPA WaterSense average of $6.06 per 1,000 gallons, the difference between 3,955 and 6,981 gallons is about $18 of water — small in isolation and a fair illustration of the pattern, because every other line moves the same way and they add up. Our annual cost guide has the consolidated figure.
What you get for it
This is the size where an above-ground pool becomes a pool rather than a large paddling pool. At 52 inches the water is chest-deep on most adults, several people can be in it without it being crowded, and it is the only class on this site where swimming rather than standing is genuinely on the table — our lap swimming guide covers how far that actually goes, and it is further than at 15 feet and still not a lap pool.
It is also the size that changes the cost-per-swim arithmetic in your favor, provided the use is there. A pool that four people use regularly divides its cost across a lot of swims; our cost per swim guide is explicit that the denominator matters more than the numerator.
What we are scoring
We have not tested these and do not claim to. The scores are our reading of published specifications — frame construction, wall height, rated volume, supplied filtration and set-up requirements — against a household leveling their own ground. Our methodology page explains how our scoring works.
Depth is the other axis, and it is the one the diameter hides. Our 52-inch pool roundup covers what a full deep wall changes about what you can actually do in the water, and about what the ground underneath has to hold.
The picks, in full
Scores are our own reading of published specifications. They are not test results — we have not tested these products and we do not claim to.
Pick #1 · A family that will still be using it in year three
Intex Ultra XTR Frame Pool Set, 18ft x 52in
Intex
The biggest, sturdiest thing in this class that a homeowner can still put up in a weekend. It is also, by a wide margin, the most expensive one to run.
#ad how this is funded · price as of October 8, 2026
Key specs
- Water capacity
- 6,981 gallons
- Pump supplied
- 2,100 GPH sand filter
- Frame
- Galvanized steel, powder-coated inside and out
- Liner
- 3-ply, puncture and tear resistant
- Manufacturer setup claim
- Ready for water in 60 minutes
- Pump wattage
- Not published by Intex
How it scoresour reading of published specs, not a test result
- Build
- 9.0
- Setup
- 6.0
- Upkeep
- 7.5
- Running cost
- 5.0
- Value
- 8.5
Overall 8.4 / 10
What works
- 6,981 gallons is genuinely swimmable for adults, not just a cooling-off pool
- Sand filter rather than a cartridge, so there is no cartridge to buy every few weeks
- Galvanized frame with inner and outer powder coating is the most corrosion-resistant construction in this price class
- Ships with the ladder, cover and ground cloth that cheaper kits make you buy separately
What doesn't
- 52 inches of wall on an 18-foot circle is a lot of water pressure — the ground under it has to be genuinely level
- Intex publishes flow rate but not wattage, so you cannot compute your running cost until the pump is in your hands
- Too heavy and too large to take down and put up casually
Skip it if: Your yard is not close to level, or you want a pool you can pack away mid-season. Nearly 7,000 gallons is not a thing you move.
What it costs to run: It is the most water in this roundup, so it is the most chemicals, the most evaporation and the largest pump. Using ENERGY STAR's own published figures for above-ground pool pumps (an ENERGY STAR model saves about $20 a year, being 11% more efficient), a standard above-ground pump implies roughly $182 a year in electricity — and that is before you scale for a 2,100 GPH sand filter running on a pool this size. Price the season before you price the pool.
Several seasons: Buy-once. Built and warranted to come back out of the box for a few years, if you store it properly.
Specs from: Intex — Ultra XTR Frame 18' x 52' specifications, ENERGY STAR — Pool Pumps
Pick #2 · Getting off the cartridge treadmill
Intex Krystal Clear Sand Filter Pump
Intex
Sand filtration replaces a recurring cartridge purchase with a backwash valve and a bag of sand that lasts years. On a pool you intend to keep, the arithmetic favors it.
Key specs
- Media
- Filter sand (or glass media)
- Maintenance
- Backwash rather than rinse-and-replace
- Media life
- Several seasons before replacement
- Wattage
- Not published by Intex
How it scoresour reading of published specs, not a test result
- Sizing fit
- 8.5
- Running cost
- 8.0
- Maintenance
- 8.5
- Build
- 8.0
- Value
- 8.5
Overall 8.4 / 10
What works
- No cartridges to buy, which removes the single largest recurring equipment cost
- Backwashing takes about two minutes versus rinsing a cartridge in the yard
- Sand lasts years rather than weeks
What doesn't
- Backwashing sends water down the drain, and that water has chemicals in it you paid for
- Higher purchase price than a cartridge pump of the same flow
- Heavier and needs a stable, level base of its own
Skip it if: A small seasonal pool that comes down every autumn. The payback period is measured in seasons, so it only works if there will be seasons.
What it costs to run: The comparison to run: cartridge replacements per season versus one bag of sand every few years, plus the water each backwash discards at the EPA WaterSense average of $6.06 per 1,000 gallons. On a pool you will own for three or more years, sand usually wins.
Several seasons: Buy-once. Built and warranted to come back out of the box for a few years, if you store it properly.
Specs from: EPA WaterSense — cost per 1,000 gallons
Pick #3 · Protecting the liner from below
Pool Ground Cloth / Under-Pool Pad
Various
Most liner punctures come from underneath, from a stone or a root you did not see. A ground cloth is the cheapest way to avoid the most expensive repair in above-ground pool ownership.
Key specs
- Function
- Barrier between ground and liner
- Sizing
- Should extend past the pool footprint
- Included with
- Some kits — check before buying separately
How it scoresour reading of published specs, not a test result
- Retention
- 8.0
- Durability
- 7.5
- Handling
- 8.5
- Running cost
- 10.0
- Value
- 9.0
Overall 8.5 / 10
What works
- Prevents the failure mode that ends pools: a puncture in the floor you cannot reach to patch
- Also slows grass and weeds growing up under the pool
- Included free in better kits, so check before you buy one
What doesn't
- Not a substitute for actually clearing stones and roots first
- Thin ones tear during installation before the pool is even up
- Traps moisture, which kills the grass underneath regardless
Skip it if: Fixing uneven ground. It protects against punctures; it does nothing about level, and level is the bigger problem.
What it costs to run: Compare its cost to a liner replacement, which is the single largest unplanned expense in above-ground pool ownership. It is not a close call.
Several seasons: Buy-once. Built and warranted to come back out of the box for a few years, if you store it properly.
Pick #4 · The single highest-return accessory here
Bubble Solar Cover for Above-Ground Pools
Various
It cuts evaporation, and evaporation is simultaneously your water bill, your chemical bill and your heat loss. Nothing else on this site reduces three costs at once.
#ad how this is funded · price as of October 8, 2026
Key specs
- Construction
- Bubble sheet, thickness published in mil
- Thickness
- Higher mil lasts longer — 12 mil and 16 mil are common
- Fit
- Cut to size; buy oversize and trim
- Orientation
- Bubbles face down, toward the water
How it scoresour reading of published specs, not a test result
- Retention
- 9.0
- Durability
- 7.0
- Handling
- 6.0
- Running cost
- 9.8
- Value
- 9.5
Overall 9.0 / 10
What works
- Reduces evaporation, which is the mechanism behind the water, chemical and heat savings all at once
- Cheap relative to everything it saves
- Can be cut to fit any pool shape, so sizing is forgiving
What doesn't
- Awkward to get on and off without a reel, and awkward is how covers end up unused
- Degrades in UV like every vinyl product
- Not a safety cover and will not support weight — this is important
Skip it if: Being a safety barrier. A solar cover looks solid and is not; a child or pet on it goes through and under.
What it costs to run: The one accessory with a clear payback. Every gallon that does not evaporate is a gallon you do not replace at the EPA WaterSense national average of $6.06 per 1,000 gallons, and it is chlorine you do not re-dose. If you buy one thing from this hub, buy this.
Several seasons: Buy-once. Built and warranted to come back out of the box for a few years, if you store it properly.
Specs from: EPA WaterSense — cost per 1,000 gallons
Questions people actually ask
How many gallons is an 18-foot above-ground pool?
Does an 18-foot pool need a sand filter?
How level does the ground need to be for an 18-foot pool?
Is an 18-foot pool worth it over a 15-foot?
Sources
Read next
- Above-ground pools for ordinary backyardsSoft-side, metal-frame and steel-wall pools compared by what they cost across a whole season, not at the till.
- The best above-ground pools for an ordinary backyardFrame pools ranked on published specs and season running cost, from a 1,700-gallon first pool to a 7,000-gallon family one.
- The 15-foot class, and the three things that stop being optionalThe 14 and 15-foot pools compared, and what doubling the water from a 12-footer actually commits you to.
- What size pool your backyard can actually takeThe three-foot rule, the level-ground tolerance, and a table matching yard size to pool size with the running cost attached.
- Leveling the ground, and the weight that makes it matterThe tolerance manufacturers publish, the weight of water that enforces it, and the method for getting a circle genuinely flat with hand tools.
- You cannot swim lengths. You can swim continuously.What above-ground depth and diameter actually allow for swimming, and the tether that turns a round pool into a continuous-swim pool.
- One size up is not a premium, it is a subscriptionThe recurring multiplier attached to each size step, priced out - and the two cases where paying it is clearly right.
- Equipment for a big above-ground pool, where the small-pool answers stop workingThe filtration, timing and cleaning kit for a 6,000-gallon-plus above-ground pool, and why the small-pool defaults stop applying.
- Sand vs cartridge: it is a maintenance choice, not a quality oneThe honest comparison: consumable cost, backwash water, weekly effort, and the season count where sand starts to win.
- The 24-foot pool, and the yard that has to hold it24 ft round pools from frame sets to steel-wall kits, compared on published gallons, what ships in the box, and the ground preparation the size actually demands.