Retaining Wall Calculator

Yes. Count the caps separately from the wall blocks. Divide the wall length by the cap length and round up. A 20-foot wall with 16-inch caps needs 15, and one with 12-inch caps needs 20. Then add roughly 10 percent for cuts and breakage, and subtract the cap row from your course count.

Caps sit on top and take the most weather. Florida summer rain and sun work dry-set caps loose, so glue them with an exterior masonry adhesive. Near the Gulf, salt air and constant moisture show up first on poorly set caps. Corners and step-downs need cut or corner caps, so count those on their own. Some HOAs specify cap color, so check before you order.

A retaining wall block calculator multiplies wall length by wall height, then divides by the face area of one block. A 20-foot wall that is 3 feet tall has 60 square feet of face. With 16 by 6 inch blocks, that is 90 blocks, or 99 with 10 percent added for waste.

These counts leave out the buried base course and the caps. The base course goes below grade, so it is one more course than the height suggests. Sandy soil will not hold a block base on its own, so that first course sits on compacted crushed stone.

Multiply length by height in feet to get face area. Divide by the face area of one block: 0.67 square feet for a 16 by 6 inch block. Round up, add 10 percent, then add caps and the buried base course. Example: 30 feet by 2 feet is 60 square feet, so 90 blocks before extras.

• Face area = length x height
• Blocks = face area ÷ block face area
• Add 10 percent for cuts and breakage
• Add one buried base course and the caps

A calculator counts blocks, not the stuff behind them. In Florida's sandy soil the trench needs compacted crushed stone, and the back of the wall needs drain stone and pipe so summer rain has somewhere to go. Those materials come on top of the block count.

The block size changes the count more than anything else. Per 100 square feet of wall face, a 12 by 4 inch block takes 300 blocks, a 16 by 6 inch takes 150, and an 18 by 6 inch takes 134. Check the face size on the product you will buy; the wrong size means the wrong count.

Bigger blocks mean fewer pieces to set, but they weigh more and are harder to move across soft sand. Small blocks suit low garden walls. Taller walls usually call for the heavier, deeper units, and the maker's spec for setback and drainage applies either way.

Find the circumference, 2 times 3.14 times the radius, then divide by the block's face length for blocks per course. A 10-foot radius circle is 62.8 feet around, which is 48 blocks per course using 16-inch blocks. Multiply by the number of courses. Check the block's minimum radius first.

For a partial curve, use the fraction of the circle. A quarter circle is one quarter of the circumference. Straight-wall blocks leave wedge-shaped gaps behind a tight curve, and those gaps need to be filled with stone. Some blocks are made for curves and others are not, so the block maker's minimum radius decides whether your circle is possible.

Count about 1.5 blocks for every square foot of wall face when using 16 by 6 inch blocks. A 20-foot wall that is 3 feet tall is 60 square feet, so about 90 blocks. Add 10 percent for waste, one buried base course, and cap blocks along the top. Smaller blocks need more.

Height matters more than length. Taller walls hold back more soil and water, and many places require an engineer or a permit once a wall passes a set height. That height is set by your county or city, so ask before you buy. If you are in an HOA, get approval for the wall's height and block color first.

We can't speak for Home Depot's online tool, but a retailer calculator is usually tuned to the blocks that store sells. The math is the same in any calculator: wall face area divided by the face area of one block. Read the face size off the block label, and confirm local stock before you order.

A store calculator gives you a block count and not much else. It will not tell you how deep the base trench goes, how much drain stone you need, or whether your wall needs an engineer. In sandy Florida soil and heavy summer rain, those are the parts that decide whether a wall stays straight.

Enter the wall in feet, multiply length by height to get square feet, and divide by the block face in square feet. A 40-foot wall 3 feet high is 120 square feet. With 16 by 6 inch blocks (0.67 square feet each) that is 180 blocks. Measure height from the buried base course to the top of the cap.

The stone figures assume one foot of drain stone behind the wall, divided by 27 cubic feet per yard. Your block maker may call for more, so use their spec. Sand drains well, but it also washes out, so the stone behind the wall is there to let summer rain leave without carrying soil with it.

We can't give one honest price per square foot, because it swings with block type, wall height, drainage, site access, and whether an engineer is needed. The block count is the easy part. Base stone, drain pipe, backfill, delivery and labor add up too. A site visit gives a real number.

• Blocks and caps: your count times the unit price
• Base stone and drain stone, by the cubic yard
• Drain pipe, fabric and backfill
• Delivery, and hauling away spoil
• Engineering or a permit, if the wall height calls for it
• Labor, which rises with height and tight access

In Florida, sandy soil usually means more base prep, and summer rain means drainage is not optional. To get the wall priced, call Dennis at Epic Horizons Landscaping, (941) 946-8403, with the length, height and a photo of the spot.

Menards is a Midwest chain, and as far as we know it has no stores in Southwest Florida, so its block lineup likely isn't what you can buy here. Use the same math with a local block: wall face area divided by the block's face area.

A 40 square foot wall in 16 by 6 inch blocks needs 60 blocks, or 66 with 10 percent for waste. Take that number to a local supplier and confirm the face size, the cap, and what is in stock. Blocks from different makers do not mix, so buy the whole wall from one product line.