When preparing your above-ground pool for the cold season, one critical question always comes up: what size pool pillow should I use? Choosing the right inflatable pool pillow is not just about convenience, it is about protecting your pool walls from destructive ice pressure. A pillow that is too small will not absorb the expansion, and one that is too large can be difficult to secure under the cover. This guide will walk you through measuring your pool, matching it with standard pillow sizes, and avoiding common winterization mistakes.
A pool pillow, also known as an ice compensator, sits on the water surface under your winter cover. When the water freezes, the pillow compresses instead of the ice pushing outward against your pool walls. Getting the size right ensures the pillow can handle the ice expansion without leaving vulnerable gaps. Below, you will find sizing charts, expert tips, and answers to the most common questions about pool pillow sizing.
Why the Right Pool Pillow Size Is Critical
Sizing your pool pillow correctly directly impacts how well your pool survives the winter. Ice can exert thousands of pounds of force. A properly sized pillow absorbs that lateral movement, relieving stress on the walls and skimmer. If your pillow is undersized, ice will form around it and push against the pool structure. This can lead to cracked walls, twisted frames, and expensive spring repairs.
How Pool Pillows Prevent Ice Damage
The science is simple. Water expands by about 9 percent when it freezes. In an above-ground pool without a pillow, that expansion force pushes directly outward on the walls and liner. Placing a large air-filled pillow on the water gives the ice a place to compress inward. The pillow deflates slightly under pressure, absorbing the expansion and keeping your pool safe. For this to work, the pillow must cover a significant portion of the water surface, which is why size matters so much.
The Consequences of Choosing the Wrong Size
An undersized pillow leaves large areas of water exposed. That exposed water turns into solid ice that rams into the walls. Even if you use multiple small pillows, the gaps between them can create pressure points. Conversely, a pillow that is too large for the pool can bunch up against the cover, tear, or float unevenly. Both scenarios compromise protection. Sizing is about finding the right balance so the pillow sits centered and stable under the cover.
How Pool Pillows Are Measured
Most manufacturers list pool pillows by diameter, typically in feet. A 4-foot by 4-foot pillow actually measures 4 feet across. However, the working size is slightly smaller once inflated and placed under tension. You will also see pillows described by their deflated dimensions, which gives you an idea of how they will fit inside the pool after you place the cover. Understanding these numbers helps you avoid buying a pillow that looks right in the box but disappoints in the water.
Understanding Diameter and Deflated Dimensions
- Inflated Diameter: This is the width across the pillow when fully inflated. For example, an 8-foot pillow measures about 96 inches across. It will cover a circular area of roughly 50 square feet.
- Deflated Length and Width: When air is let out, the pillow flattens to a roughly rectangular shape. A large pillow might deflate to 100 inches by 80 inches, which still covers a broad surface area under a winter cover.
- Thickness: Standard pool pillows are between 8 and 12 inches thick when inflated. Thicker pillows can absorb more ice expansion but must not lift the cover excessively.
Always check the product description for both inflated and deflated specs. If you have a tight-fitting safety cover, the deflated footprint is especially important. You want the pillow to stay flat and wide after you let out most of the air, which we will discuss in the installation section.
Standard Pool Pillow Sizes and Your Pool Dimensions
Pool pillows come in a handful of standard diameters. Matching these to your pool’s size and shape is the fastest way to answer, “what size pool pillow should I use?” The general rule is that the pillow should cover between 40 and 60 percent of the water surface area. That gives enough absorption capacity without overstuffing. Here is a breakdown by common pool sizes.
Sizing for 12-Foot to 18-Foot Pools
For smaller round pools with diameters from 12 to 18 feet, one 4-foot by 4-foot pillow is often sufficient. However, if you live in an area with severe freezes, consider a 5-foot by 5-foot pillow or even a 6-foot by 6-foot option. A single 4-foot pillow covers about 12.5 square feet, which is roughly 13 to 20 percent of the water area. In a 15-foot pool, that is on the lower end. Adding a second smaller pillow can boost coverage without needing a massive inflatable. For an 18-foot pool, one 6-foot pillow provides a better safety margin.
- 12-foot round pool: one 4 ft x 4 ft pillow, or two 4 ft pillows for heavy ice regions.
- 15-foot round pool: one 5 ft x 5 ft pillow, or two 4 ft pillows.
- 18-foot round pool: one 6 ft x 6 ft pillow, or two 5 ft pillows tied together.
Sizing for 21-Foot to 24-Foot Pools
In this popular size range, you will want at least an 8-foot by 8-foot pillow. An 8-foot pillow covers about 50 square feet, which is around 15 percent of a 21-foot pool’s surface. While that sounds low, the pillow’s large footprint when partially deflated spreads the ice pressure effectively. Many pool owners pair an 8-foot pillow with a secondary 4-foot pillow placed to one side to cover more area. For a 24-foot round pool, one 8-foot by 8-foot pillow is the minimum recommendation, but an 8-foot by 10-foot or 10-foot by 10-foot pillow is even better if your cover allows it.
- 21-foot round pool: one 8 ft x 8 ft pillow, plus optional 4 ft pillow.
- 24-foot round pool: one 8 ft x 8 ft pillow minimum; 10 ft x 10 ft recommended for harsh winters.
Sizing for 27-Foot to 33-Foot Pools
Larger above-ground pools need the biggest pillows available. For a 27-foot or 28-foot pool, a single 10-foot by 10-foot pillow is a solid choice. For 30-foot and 33-foot pools, many winterization experts recommend using two pillows, one 10-foot and one 8-foot, placed side by side and tethered to the center. Some manufacturers make oversized 12-foot by 12-foot pillows specifically for these big pools. If you can find a 12-foot pillow, it gives excellent single-pillow coverage for a 30-foot pool. Otherwise, dual pillows are the safe bet.
- 27-foot round pool: one 10 ft x 10 ft pillow, or two 8 ft pillows.
- 30-foot round pool: one 12 ft x 12 ft pillow if available, otherwise one 10 ft and one 8 ft pillow.
- 33-foot round pool: two 10 ft pillows, or one 12 ft and one 8 ft pillow.
Special Considerations for Oval and Irregular Pools
Oval pools require a slightly different approach. The length of the pool means ice can form in long sheets. Instead of a single giant pillow that may not fit the shape, use two pillows spaced along the long axis. For a 15-foot by 30-foot oval pool, place a 10-foot pillow in the center and a 6-foot pillow toward one end. This distributes the ice compensation more evenly. If your pool is rectangular with squared corners, a single massive pillow works, but still aim for at least 50 percent coverage of the total surface area.
For irregular shapes or pools with deep ends, consider an extra pillow near the deepest section where ice tends to be thickest. Always follow your pool manufacturer’s winterization guidelines alongside pillow sizing. The cover also plays a role. A tight safety cover can handle a slightly larger pillow footprint; a loose tarp cover may require more precise sizing to prevent pulling.
A Step-by-Step Guide to Measuring Your Pool for a Pillow
If you want absolute certainty before ordering, measure your pool yourself. This simple process takes only a few minutes and guarantees you buy the right size.
Measuring Across the Center
- For round pools, run a tape measure from one inside edge of the top rail straight across the center to the opposite inside edge. This gives you the inner diameter. Most pools are labeled by outer diameter, but the water surface is slightly smaller. For example, a 24-foot pool often has an inner diameter around 23.5 feet.
- For oval pools, measure the length and width at the widest points inside the top rail. Note both numbers.
Factoring in Wall Height and Cover Type
Wall height, typically 48 or 52 inches, influences ice thickness. Deeper pools form thicker ice, so you might want a pillow with a higher profile or one that covers more area. Also, consider whether you use a solid cover with a water bag or a mesh safety cover. Mesh covers allow rain and snow to pass through, which can cause the pillow to shift. Under a mesh cover, oversizing slightly and using multiple tie-down points helps the pillow stay centered.
How Many Pool Pillows Do You Need?
Most pool owners assume one pillow is enough, but in many cases two smaller pillows provide better coverage than one giant one. The ideal configuration depends on your pool shape and climate. In freeze-thaw regions like the Northeast or Midwest, double pillows give redundancy. If one develops a small leak, the other still protects the pool. For round pools under 21 feet, one pillow is usually sufficient. For larger rounds and all ovals, consider two.
When using two pillows, tie them together through the corner grommets using nylon rope. Then tether the pair to the pool sides so they cannot drift to one end. This technique creates a single large flexible ice compensator that spreads out under the cover.
Tips for Installing and Securing Your Pool Pillow
Once you have answered “what size pool pillow should I use,” the next step is proper installation. Even the right pillow fails if it floats out of position. Begin by inflating the pillow only about 60 to 70 percent of its capacity. A fully inflated pillow is harder to control and more likely to pop under ice pressure. After placing it in the center of the water, attach ropes through the grommets and tie them to opposite sides of the pool. Then pull the cover over the pillow and deflate it slightly more until it sits flat against the underside of the cover.
For detailed inflation steps, check out our guide on properly inflating your pool pillow. Following the right air pressure tips prevents the pillow from popping in extreme cold. When the season ends, you will need to know the best way to store it. Improper storage can lead to mildew and cracks. Our guide on storing your pool pillow properly walks you through cleaning, drying, and packing it away so it lasts for many winters.
Common Mistakes to Avoid When Sizing Pool Pillows
- Relying on pool size alone without measuring: A 24-foot pool that is actually 23.5 feet inside changes the coverage percentage. Always measure.
- Using a single tiny pillow in a big pool: A 4-foot pillow in a 27-foot pool leaves nearly all the water unprotected. It will do almost nothing.
- Overinflating to make the pillow look bigger: This increases the risk of bursting and does not add usable coverage. The pillow should be soft and pliable.
- Ignoring the cover type: Solid covers and leaf nets pull differently. Adjust pillow size or tie-downs accordingly.
- Forgetting to factor in snow load: Heavy snow can push the cover down, forcing the pillow to the side. A properly deflated pillow will stay put better.
Frequently Asked Questions About Pool Pillow Sizing
What is the most common pool pillow size?
The 4-foot by 4-foot and 8-foot by 8-foot pillows are the most widely sold sizes. They fit the majority of small to mid-sized above-ground pools and are available at most pool supply stores. However, always verify your pool diameter before buying because a 4-foot pillow is too small for anything larger than an 18-foot pool in harsh winter climates.
Can I use a beach ball or old inner tube instead of a pool pillow?
No. Pool pillows are made of heavy-duty vinyl designed to withstand prolonged cold and pressure. Beach balls and inner tubes will burst under ice expansion and are not recommended. Always use a product specifically sold as an ice compensator or winter pool pillow.
How do I know if my pillow is too small?
If after placement you can see wide water gaps around the pillow, or if the pillow only covers the very center of a large pool, it is too small. For round pools, a quick way to check is to imagine a circle that covers at least 40 percent of the water. Your pillow, when deflated and flat, should roughly cover that much area. When in doubt, size up.
Does water level affect pillow sizing?
Yes. You must lower the water level below the skimmer and return jet before placing the pillow, typically 4 to 6 inches below the skimmer. This creates space for the pillow to sit under the cover without touching the top rails. The pillow size you choose assumes you have followed the proper water level reduction. If the water is too high, even a perfectly sized pillow will push the cover up and cause problems.
Should I use a pool pillow in a saltwater pool?
Yes, but rinse the pillow thoroughly after removal. Salt can degrade the vinyl over time. The sizing recommendations remain the same; saltwater does not freeze differently, so the ice expansion mechanics are identical.
Conclusion
Answering “what size pool pillow should I use” starts with knowing your pool’s true inner diameter and understanding how ice expansion works. For pools up to 18 feet, a 4-foot to 6-foot pillow works. For 21 to 24 feet, go with an 8-foot pillow minimum. Larger pools need a 10-foot or 12-foot pillow, or two pillows working together. Always measure first, inflate partially, and secure the pillow tightly under your cover. These steps protect your investment and save you from costly spring repairs.
Remember, winterization is a system, not a one-step fix. Combine the right pillow size with a quality cover, proper water chemistry, and correct storage of pool equipment. For more guidance, refer to our detailed pool pillow inflation instructions and seasonal pillow storage tips. You can also review pool winterization expert advice to double-check your entire closing process. With the right pillow and setup, your pool will emerge from winter strong and ready for summer.