For the past several years, vinyl-liner pools have become ever more intricate in their design. In fact, some builders rarely install standard shapes anymore.

Considering this reality, it’s crucial that installers know how to measure pools for both new and replacement liners, no matter how complex the perimeter shape and inner contours.

Doing this involves a process known as A-B measuring.

This method requires installers to establish two reference points (called A and B) away from the pool, then designate a number of points around the pool perimeter. A two-person team measures from A to every perimeter point, then from B to every perimeter point. All distances are recorded on a form provided by the manufacturer, who will then use the information to create a schematic of the pool and, therefore, the liner.

Following is a detailed explanation of this method.

Step 1: Place the A and B points

To set up for measuring, installers must properly situate the A and B points, designated by stakes, and place enough points around the vessel.

Place the A-B stakes as far away from the pool as possible. Both should be the same distance from the pool, and there should be no obstructions between them and the vessel. Consult the liner manufacturer for the minimum distance. Some say they should be at least 3 feet away, while other builders prefer to go 10 or even 15 feet if space allows.

They also must be far enough from each other. For example, Ed Nejame, a partner with Nejame & Sons in Danbury, Conn., places his A and B points at a distance approximating 3/4 the length of the pool. Other professionals will put them closer together, as long as they’re at least 10 feet apart.

Nejame likes the distance between stakes to be in full feet. For instance, point A and point B should be 20 feet apart, not 20 feet, 3 inches apart. This keeps things as simple as possible — it’s easier to measure later if needed, and then communicate this to the manufacturer.

Place the stakes so that all lines drawn from stake to perimeter point will sit in front of both stakes. Thus, when lines are drawn from reference A to any of the perimeter points, none of those lines should cross behind stake B.

“Everything has to be out in front of those two reference points,” says Jimmie Brown, service manager for Burton Pools and Spas in Fort Smith, Ark., a Pool & Spa News Top Builder.

Make sure to pound the stakes deep enough into the ground so they don’t move. It’s crucial that they stay put through the whole process.

And try to place the reference points opposite any areas with more challenging features such as planters or a waterfeature that curves inward.

Next, installers must designate the points around the perimeter of the pool.

The more complicated the liner, the more points are needed. Mark those spots where walls change direction. For instance, on each radius, mark the beginning, end and at least one point in the middle. Also designate each side of all steps, benches and waterfeatures, and spots where floor depths begin to change. Gentle curves can be tracked about every 3 feet, while tighter ones may need points as close as 1 foot apart. It’s easily possible to end up with 50 to 70 points around the pool.

Mark the points with something that is permanent enough to refer back to for later reference, but can be removed or concealed later. Some installers use magic marker at the top of concrete walls if the pool is new and no deck has yet been built.

Other professionals use the seams on poured concrete walls.

“The gentleman who builds the wall uses forms, and some forms are only 2 feet apart,” says Jonathan Forman, installation manager for Easton Pool & Spa in Easton, Mass. “When he strips the wall, there will be seams from each panel. I usually put a point on each seam. If the manufacturer calls and says, ‘Could you do a cross measurement from point 1 to point 28?’ I’ll know exactly where those points are.”

For replacement liners, a chalk or piece of duct tape are both good options, but if using tape, be sure to mark an exact point and number on the tape.

Step 2: Measure the perimeter

For more complicated pools, it generally takes two people to complete the measurements. One works the tape measure, going from stake A to point 1, then stake A to point 2, etc., around the pool. This person should be careful around the stake, making sure that it doesn’t shift, since it’s imperative that this reference point remain absolutely stationery throughout this process. When extending the tape measure, take it in a straight line from the stake to the point, with no intrusions by planters or other obstacles. After getting the measurement, call it out.

The second person records the measurements on the form.

To avoid errors, Nejame set up a system that his company uses every time. This way, it becomes a habit, and each person knows what to expect of the other.

In his firm’s case, the person using the tape calls out the measurements in a very specific way using the fewest numbers possible to avoid confusion. “If it’s 12 feet 3 inches, you don’t say 12 feet-3,” he explains. “You say 12 ft-dash-3 inches.”

The person handling the form includes the dashes when writing measurements. This helps prevent confusion on the manufacturer’s end.

In addition, they should not call out the point number — just the measurement. “A big mistake would be for someone to say, ‘Point 15 is 14 feet-5 inches,’” he explains. “That would be bad, because they might put the number down [as a measurement]. It’s better to name the point afterwards. For example, on my 10th point, I would say, ‘25 ft-dash-2 inches. That is No. 10.’ Then I make them answer.”

He and his crews always move clockwise around the pool.

When the A measurements are completed, check the B stake to make sure it hasn’t moved. Then repeat the process, only this time from the second stake. Start with point 1 and move in the same direction you did when taking the A measurements.

Always provide true measurements, and don’t subtract to account for stretching. That was done years ago, but manufacturers now figure in stretching as part of their own process. Some suppliers even make liners differently in hot weather and cool, since they will stretch more when it’s warm.

“The builder tries to add 2 or 3 inches on his own, and by the time the vinyl manufacturer adds a little bit, there’s more of a chance for a wrinkle,” says Joe Donnelly, owner of Complete Pools and Concrete Construction in Stilwell, Kan. “So the closer you are, the better it’s going to fit.” This is especially true when fitting the liner over stairs and benches.

As far as larger steps and benches, measure where the item begins and ends, and how deep and how far into the pool it goes, and take cross measurements to indicate curves.

But installers should use a different approach for small steps and benches, since they’re more difficult to measure precisely. Cut templates out of foam and provide them to the manufacturer, who will hold the template in place when making the liner. “Use 1/4-inch foam instead of 1/8-inch, because the thin foam seems to work on you a little bit when you’re trying to cut it,” Donnelly says. “Set it on top and cut neatly around it.”

Let the manufacturer know if the front of the step or bench follows the radius on the perimeter, rather than a straight line.

Step 3: Measure inside the pool

Replicating the contours of the pool floor is a bit more complicated, since it includes issues of depth.

This process entails what are known as “out-and-down” measurements. To plot a specific point on the floor, designate two points on the perimeter, measure how far out the floor point is from both perimeter points, and then measure the depth.

Take out-and-down measurements at corners and anytime there’s an abrupt change in the depth. Consult the manufacturer to find out at what intervals they want out-and-downs in the sloping areas. Some suppliers require them 2 feet apart, others less frequently. If there’s a more drastic slope somewhere on the floor, you may need the measurements closer together.

Measuring for a replacement liner can be a little more complicated since the pool will be full of water.

Different builders employ their own methods, but they generally consist of using a vac pole with tape measures and plumb bobs.

Use the pole to find where the walls and floor meet and where depths change or sloping begins. Ways of actually taking the measurements vary. Brown has a tape measure with a fishing weight at the end, which he dangles off a vac pole. He drops the weight into the water and records the depth.

Others create a system consisting of two poles connected by a hinge. One will go across the pool to the desired point, while the other pole goes down into the water. Mark the water line on the vertical pole and then measure it. Nejame sent his measuring poles to a sign maker, who essentially printed a ruler on them. Now he doesn’t have to follow up with a tape measure.

When recording the “down” measurement on pools filled with water, be sure to include the distance between the waterline and the coping.

Take measurements on both sides even on the most symmetric pools, since differences in craftsmanship, quality of concrete or settling could lead to one side coming out differently than the other.

In addition, let the manufacturer know if the perimeter of the floor doesn’t match the coping — say, the pool corners are radiused at the coping, where they are straight on the floor.

Here again, provide true measurements.

Step 4: Wrapping it up

With all the measurements taken, installers should complete a couple more steps to help the manufacturer get the liner just right.

First, review all out-and-down measurements to make sure they reflect the pool’s length and width. Add up the “out” measurements from one end of the pool to the next. The total should equal the length of the vessel. Do the same for the width. If they don’t add up, you’ll need to measure again.

Second, put together visual aids for the manufacturer. For any atypical areas, such as an unusual corner, bench or slope, provide photos. You can also supply the “dig book” so the liner producer can see how the pool maps out.

After placing the order, double-check the measurements on the acknowledgement sent by the manufacturer. Remember, there are up to three opportunities for numbers to be misinterpreted or recorded incorrectly — from the measuring team, the builder’s data entry person and the manufacturer’s staff.