How to Measure for a Pool Cover?

Measuring your pool for a cover shouldn’t feel like guesswork – but the truth is most homeowners do guess, and that’s exactly why so many covers arrive the wrong size.

This guide for how to measure for a pool cover, fixes that for good.

Whether you’re buying a standard winter/tarp cover or a custom safety cover, this step-by-step guide from Pool Guard USA breaks down both measurement methods – simple and advanced – so you get a perfect fit the first time.

In this guide, you’ll learn:

• How to measure your pool cover size with total accuracy
• How to measure for a winter pool cover / tarp cover (the easy method)
• How to measure for a safety cover using the A-B triangulation system
• The biggest mistakes homeowners make (and how to avoid them)
• What to do for freeform pools, attached spas, and complex features

Let’s get you the right cover – with confidence.

Before You Start – Which Type of Pool Cover Do You Have?

Different pool covers require completely different measurement systems.

Here’s the breakdown:

Winter / Tarp Cover

Use this if you are buying a:

• Winter cover
• Mesh cover
• Solid tarp cover
• Above-ground cover
• Rectangular cover for a non-rectangular pool

Method used: Simple length-and-width measurement with adjustments.

Custom Safety Cover

Use this if you are buying a:

• Custom-fit safety cover
• Freeform cover
• Cover with cutouts (for spas, rocks, slides, walls, ladders, etc.)

Method used: The A-B Triangulation Method, a professional measuring system using reference points A and B to map your pool’s shape.

How to Measure for a Winter/Tarp Pool Cover (Simple Method)

Winter/tarp covers do not follow the exact shape of your pool. They’re oversized on purpose. Your job is simply to measure the longest length and widest width you need to cover – including steps, drop in water level, and obstacles.

Step 1: Measure Your Pool’s Length and Width

• Measure the overall length.
• Measure the overall width.
• For shaped pools (Roman, Grecian, Lazy-L, Freeform), use the maximum bounding box – not the curves.

Pro Tip:
Rectangular pool? Easy.
Freeform? Measure the longest and widest points of the waterline.

Step 2: Account for Water Level Drop

Winterizing typically requires lowering your water level.
If the water level drops more than 12″, you must add twice the extra drop to BOTH length and width.

Examples:

• 1 extra foot drop → add 2 ft to L & W
• 2 extra feet drop → add 4 ft to L & W
  

This ensures the cover doesn’t sag or tear under load.

Step 3: Add Step Extensions

If your pool has a step section:

Centered steps (4′ × 8′ example)

Add the full step length to the overall pool length.

Side steps

Add the step width to the overall pool width instead.

Step 4: Add Clearance for Obstacles

Railings, ladders, rockwork, or any non-removable feature within 2–3 feet of the waterline must be accounted for.

Rule:
Add twice the height of the obstacle to both length and width.

Example:
A ladder rail 3 ft tall → add 6 ft to L & W.

Step 5: Round UP to the Next Standard Cover Size

Covers come in standard sizes – if your calculation doesn’t match one, always round up.

Example:
You need a cover for 23′ × 41′ → order a 24′ × 42′ cover.

Step 6: Order Based on POOL SIZE, Not Cover Size

This mistake alone causes thousands of incorrect orders.

If your pool is 18′ × 36′:
Order “Pool Size: 18′ × 36′ Cover” – NOT “Cover Size 18′ × 36′.”

How to Measure for a Safety Cover Using the A-B Method

If you have a freeform pool or any pool with spas, waterfalls, raised walls, rockwork, ladders, or slides – you MUST use the A-B triangulation method. This method is used by LOOP-LOC, Meyco, Merlin, and every major manufacturer.

This is the most accurate system ever developed for mapping complex pool shapes.

What You Need

• Chalk or painter’s tape
• 100 ft measuring tape
• Helper
• Printed measurement form
• Graph paper (recommended)
• Smartphone camera

Step 1 – Establish Your A-B Line

The A-B line is your reference baseline. The entire shape of your pool will be triangulated from these two points.

Your A-B line must:

• Be straight
• Be at least 3 ft away from the nearest point of the pool
• Ideally be 4–5 ft away for better accuracy
• Be roughly ⅔ the pool’s length
• Never cross the pool, even if extended
• Have A on the left and B on the right when facing the pool

Snap a chalk line between A and B and record the A-B distance.

Common Failure:
A-B stakes shifting. Use stable deck points. Do NOT use loose stakes in soil.

Step 2 – Mark and Number All Perimeter Points

Walk around the inside edge of the pool and mark reference points:

• 3 ft spacing on straight sections
• 1–2 ft spacing on curves
• 6–12 inches on tight radiuses

Every change in direction gets its own point.
Number the points clockwise, starting at 1.

Step 3 – Mark All Obstructions

Number these after the last perimeter point. Examples:

• Ladders
• Handrails
• Slide legs
• Spillways
• Spa walls
• Rocks
• Raised bond beams
• Corner points
• Dive stands

Anything within ~3 ft of the waterline must be included.

Step 4 – Measure Each Point From A and B

This is where the triangulation happens.

1. Measure from A → Point 1, A → 2, A → 3, etc.
2. Then measure from B → Point 1, B → 2, B → 3…
3. Record each pair of measurements on your form.
4. Round to the nearest inch.

Spot-check several points to confirm consistency.

Step 5 – Add Cross-Dimensions (Accuracy Check)

To verify the shape:

• Measure 1–2 long diagonals
• Measure 1–2 wide diagonals
• Add optional diagonals for complex pools

Manufacturers use these to confirm your shape isn’t mirrored or distorted.

Step 6 – Create a Scaled Sketch

On graph paper or the included form:

• Draw the A-B line to accurate scale
• Sketch pool perimeter
• Add numbered points
• Add obstructions
• Add cross-dimension lines

This sketch helps the manufacturer visualize your geometry.

Step 7 – Take Photos

Manufacturers request:

• Full pool overview
• Close-ups of obstacles
• Shots of waterfalls, spas, rockwork
• A-B line visible in photos
• Overhead shot if possible (balcony, second story, drone)

Photos prevent measurement disputes and fabrication errors.

Biggest Measurement Mistakes (And How to Avoid Them)

❌ A-B line too close to pool

→ Must be 3–5 ft away; must not cross pool when extended.

❌ Counter-clockwise numbering

→ Always number perimeter points clockwise, or your pool becomes mirrored.

❌ Using soil stakes instead of stable deck points

→ Stake movement = false measurements.

❌ Skipping obstructions

The cover MUST fit around: ladders, rails, rocks, walls, spas.

❌ Not providing cross-dimensions

This is how manufacturers detect errors before cutting material.

❌ Confusing pool size with cover size

Especially common for winter covers.

Pool Cover Size Calculator (When to Use It)

A pool cover size calculator works great for:

• Rectangular pools
• Above-ground pools
• Standard winter covers

It is NOT accurate for safety covers, because safety covers require shape-specific geometry.

But for tarps, it’s a time-saving tool – just plug in your L × W dimensions.

Conclusion

A pool cover is a safety product, not just a piece of fabric – accuracy matters.

You now know:

• How to measure for a winter/tarp cover correctly
• How to measure for a safety cover using the A-B method
• How to avoid the most common (and expensive) mistakes
• What manufacturers actually need to build a perfect cover

Measure once, buy once!

If this guide for how to measure for a pool cover helped you, share it with another pool owner and feel free to explore our full safety cover solutions here at Pool Guard USA.