How to Measure a Swimming Pool Liner?

When it’s time to replace your vinyl liner, one of the most critical steps is taking accurate pool liner dimensions. A properly measured liner ensures a snug fit, smooth installation, and long-lasting durability. A poorly measured liner, however, can wrinkle, overstretch, or even tear, leading to costly mistakes and shortened liner life.

At Royal Pools G2 Landscaping, we replace multiple inground vinyl liners throughout the swim season. We know just how crucial it is to measure inground liners as accurately as possible (more on that soon). Although we do not install or measure above-ground liners, we can still provide the information on how to do so. No matter the shape–rectangular, freeform, oval, or kidney–correct liner measurements are key to a successful replacement and healthy liner.

Why Measuring a Pool Liner Correctly Matters

Vinyl liners are custom-designed to match your pool’s specific shape and size. Even if two pools look identical, small variations in dimensions can cause major fitting problems if you order a standard-size liner without double-checking that it will fit in your pool. Here’s why accuracy is so important:

• Wrinkle prevention: A liner that’s too big will bunch up and wrinkle.
• Tear prevention: A liner that’s too small will overstretch and eventually tear.
• Longevity: Correct pool liner dimensions help maximize the lifespan of your liner.
• Professional fit and look: A well-measured liner provides the seamless, smooth finish homeowners love.

Knowing how to measure a swimming pool liner means fewer headaches during installation and a pool that looks great for years.

Tools You’ll Need

Before you begin, gather these tools:

• 100 ft. flexible tape measure (fiberglass or cloth for accuracy over long distances)
• Helper (you’ll need two people for most measurements)
• Pencil and paper (or a sketch diagram of your pool)
• Level (for checking slope transitions)

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How to Measure a Swimming Pool Liner for Inground Pools

Measuring an inground pool is more complex than above-ground models because of depth variations, slopes, and built-in features like lights, extra skimmers or jets, etc. The goal is to provide exact pool liner dimensions that the liner manufacturer can use to create a liner tailored to your pool.

Step 1: Measure the Pool Length and Width

• Start with the overall length, measuring from inside wall to inside wall at the longest point.
• Next, measure the overall width, again from inside wall to inside wall at the widest point.
• For freeform or kidney-shaped pools, take multiple width measurements at different sections of the pool. Record each one on your diagram.

Step 2: Measure the Depths

Depth is one of the most important measurements when figuring out pool liner dimensions.

• Shallow end depth: Measure from the shallow end floor to the top of the coping.
• Deep end depth: Do the same at the deepest point.
• Transition slope: Measure the length of the slope that connects the shallow and deep ends. Record where the slope begins and ends.

Step 3: Measure Wall Heights

For inground vinyl liners, the wall height ensures that the liner lines up with the coping tracks.

• Place the tape at the bottom corner where the wall meets the floor and measure straight up to the coping.
• Repeat this measurement at several points around the pool to ensure consistency.

Step 4: Record the Shape and Features

Draw a basic diagram of your pool and label each measurement. Include details such as:

• Pool shape (rectangle, oval, freeform, or kidney-shaped)
• Step sections (inside steps, corner steps, or recessed steps)
• Benches or tanning ledges
• Radii of corners (for rectangular pools, measure the curved section instead of assuming a perfect right angle)

Pro Tip: The more detail you provide in your diagram, the better your custom vinyl liner will fit.

How to Take AB Measurements (for Freeform, Kidney, or Complex Shapes)

For irregular shapes like freeform or kidney pools, use the AB measurement method, which helps manufacturers map out the exact perimeter.

1. Select A & B points: Mark two stakes (points A and B) on the deck, at least 4-5 ft from the edge, about two-thirds the length of the pool apart. When facing the pool, A should be on the left.
2. Draw your AB line: Use a chalk line connecting A and B. Record the distance between them.
3. Mark perimeter points: Starting halfway along the A-B line, mark points on the perimeter at regular intervals—approximately 2–3 ft apart on straight sections, and closer (1 ft) around curves. Number each point sequentially, including corners, slope break points, and features.
4. Measure distances to A and B: For each numbered point, measure the distance to A and then to B. Record each measurement next to its point number.
5. Other measurements:

• Mark slope break points, like shallow-to-deep transition.
• Include hopper pad dimensions, shallow depth to center, and corner-to-corner distances as needed.

1. Diagram: Draw a scaled sketch indicating the A-B line, pool shape, numbered points, and important features or obstructions.

This A-B method provides a reliable map of complex shapes for accurate vinyl liner measurements.

Common Mistakes to Avoid with Inground Pool Measurements

1. Guessing instead of measuring – Never rely solely on old invoices or pool model names.
2. Ignoring the slope – Depth transitions must be measured precisely.
3. Measuring from outside edges – Always measure inside wall to inside wall.
4. Forgetting corner radius – Rounded corners need exact measurements, not estimates.
5. Skipping built-in features – Steps, benches, and ledges need their own measurements for custom liner cutouts.

How to Measure an Above-Ground Pool Liner

For homeowners curious about how to measure an above-ground pool liner, the process is more straightforward. Most above-ground pools come in standard sizes, but confirming your measurements ensures you buy the right vinyl liner.

Step 1: Measure the Diameter (Round Pools)

• Stretch your tape measure across the pool, passing directly through the center point.
• Take at least two measurements across different points to ensure accuracy.

Step 2: Measure the Length and Width (Oval Pools)

• For ovals, measure the longest length from end to end.
• Then, measure the widest width at the pool’s center.

Step 3: Measure the Wall Height

• Place your tape at the bottom track inside the pool wall (not the ground).
• Measure up to the top track or rail.
• Standard above-ground vinyl liner wall heights are 48″, 52″, and 54″.

Step 4: Double-Check Your Measurements

• Always measure in two directions to confirm accuracy.
• Write down every number—don’t rely on memory.

Mistakes to Avoid with Above-Ground Pool Measurements

• Measuring outside the pool frame instead of the inside wall dimensions.
• Measuring to the ground instead of the bottom track.
• Assuming all pools are standard… even the smallest differences can affect how the liner fits in the pool.

Inground vs. Above-Ground: Key Differences

• Inground pools require highly detailed pool liner dimensions, including depth transitions, corner radii, and custom features.
• Above-ground pools are typically simpler, with diameter and wall height being the key measurements.
• Both require accuracy, but inground liners are more likely to be custom-made, while above-ground liners are often pre-manufactured in standard sizes.

Final Thoughts

Knowing how to measure a swimming pool liner is the first step toward a smooth installation and a long-lasting vinyl liner.

• For inground pools, focus on length, width, depth, wall height, slopes, and built-in features. Precision here is essential, as even small errors can lead to poor liner fit.
• For above-ground pools, accurate diameter (or length/width for ovals) and wall height are the most critical measurements.

Whether you’re learning how to measure above-ground pool sizes or figuring out exact pool liner dimensions for an inground model, take your time, double-check each measurement, and sketch everything clearly. Providing precise information to your installer or liner manufacturer will save time, money, and frustration while keeping your pool looking beautiful for years to come.

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Written by Logan Edgemon