How to Measure for a New Pool Liner (Without Screwing It Up)

Replacing your swimming pool liner is one of those jobs you really only want to do once (or never). If you get the pool liner size wrong, you're either stuck with a liner that doesn’t fit, or you’re wrestling wrinkles, leaks, or costly returns. Whether you're shopping for an above ground pool liner or an in-ground liner, getting accurate measurements is step one to doing it right.

Why Measuring Matters More Than You Think

A perfectly sized pool liner creates a smooth, tight finish and keeps your pool looking great for years. A bad fit can lead to creases, gaps, and premature wear. Many pool owners guess or assume their pool is a standard size, only to find out mid-install that things don't line up. Every pool is slightly different, especially older models or DIY above ground setups. Measuring isn't optional. It's essential.

What You'll Need

• Flexible measuring tape (long enough for your pool size)
• Step ladder (if measuring a deep end)
• Pen and notepad or your phone to record numbers
• Helper (recommended for accuracy)

How to Measure an Above Ground Pool Liner

1. Measure the Diameter

If your pool is round, measure across the center from wall to wall at the widest point. Do not measure from the top rails. Use the inside edges of the wall as your starting and ending points. Double check by measuring again at a 90-degree angle to your first measurement.

2. Measure the Length and Width

If your pool is oval or rectangular, measure both the length and the width from inside wall to inside wall. Avoid measuring the top ledge. You want the inner dimensions of the water space, not the outer frame.

3. Measure the Wall Height

This one trips a lot of people up. Measure the height of the wall from the floor to the top of the metal wall (not the top rail). Most above ground pools have wall heights of 48, 52, or 54 inches. Be sure to measure straight up and down, not on an angle.

How to Measure for an In-Ground Pool Liner

In-ground pool liners are custom-fit, which means accurate measurements are even more important. If your pool has a complex shape or slope, hiring a pro may be your best bet. But if you want to DIY the measurements, here’s what to do.

1. Draw Your Pool Shape

Sketch the shape of your pool from above. Label key areas like steps, shallow end, deep end, and any curves or slopes. This helps you keep track of which measurements go where.

2. Measure the Length and Width

Just like with above ground pools, start by measuring the longest and widest points. Take measurements along the waterline, not the coping.

3. Measure the Depth

Measure from the floor to the waterline in both the shallow and deep ends. If the floor has a gradual slope, measure at multiple points and mark those on your diagram. For hopper-style deep ends, you’ll need diagonal measurements too.

4. Take Diagonal Measurements

This is where a helper really comes in handy. Measure diagonally across your pool in multiple directions to confirm symmetry. If your diagonals are off by more than an inch or two, something might be uneven.

Common Mistakes to Avoid

• Guessing your pool size: Even "standard" pools can be slightly off.
• Measuring from the outside: Always use inside wall-to-wall dimensions.
• Forgetting the wall height: This is critical for above ground liner fit.
• Not labeling measurements: You’ll mix them up later if you don’t organize them clearly now.

Need a Quick Reference? Here’s a Measurement Checklist:

• Round pool: Diameter and wall height
• Oval pool: Length, width, wall height
• In-ground pool: Length, width, shallow depth, deep depth, slope length, diagonals

When in Doubt, Ask

If your measurements don’t seem right or you’re unsure what liner style fits your pool, contact a pool liner expert. It’s way cheaper to double check now than to reorder an entire liner later.

And if you’re replacing a liner for the first time, check out our guides on overlap vs beaded liners and how to install an above ground pool liner.

Final Tip

Write down your exact pool measurements and keep them saved. You’ll thank yourself next time around. Pool liners don’t last forever, but getting the right fit can make yours last a whole lot longer.

Need help finding the perfect liner? Our team is here to help you choose the right size and type for your pool.