Sakrete Concrete Mix Bag Counts for Posts and Slabs

About two 80 pound bags of Sakrete concrete mix set one 4 by 4 fence post in a 2 foot hole. A 9 by 9 foot slab poured 4 inches thick takes 49 bags. Each 80 pound bag of Sakrete High-Strength Concrete Mix yields 0.6 cubic feet of concrete, and you can work any post or slab count from that number.

We sell Sakrete High-Strength Concrete Mix in the 80 pound bag at our yard in Hot Springs Village. Measure the job before you come, and you can leave with the bags and the gravel for your post holes on one trip.

What one bag of Sakrete concrete mix makes

A cubic foot is a box 12 inches on each side. One 80 pound bag of mixed concrete fills a little more than half of that box. The same mix comes in a 60 pound bag that yields 0.45 cubic feet and a 40 pound bag that yields 0.30 cubic feet. The 80 pound bag yields twice the concrete of the 40 pound bag, and a job needs half as many bags. The 9 by 9 foot slab takes 49 of the 80 pound bags, and it would take 98 of the 40 pound bags.

Sakrete calls this mix its original bagged high strength concrete, and it says pros have trusted it since 1936. Sakrete rates it at a final strength of 4,000 PSI. The mix works in pours 2 inches thick and over, and a 4 inch slab and a 2 foot post hole both fall well inside that range.

Slabs, footings, walkways and sidewalks all take this mix, and so do post setting, repairs, stairs and ramps. Contractors who plan in cubic yards can count 45 bags of the 80 pound mix to the cubic yard. A fence post and a patio slab each take their own bag math.

How many bags of concrete a fence post takes

Check your local building code before you dig. Take any question about post depth or footings to your local building official. Then size each hole with two Sakrete rules of thumb.

Make the hole about three times as wide as the post. A 4 inch post takes a 12 inch hole. Dig the hole about one third as deep as the post stands above the ground. A 6 foot fence takes a 2 foot hole, and you buy an 8 foot post to reach the bottom of it.

Pour 4 to 6 inches of gravel into the bottom of the hole, because the gravel lets water drain away from the end of the post. Pack the gravel down with the end of the post, and the hole is ready for concrete.

Now work the count for that 6 foot fence on 4 by 4 posts. A 12 inch round hole dug 24 inches deep, with 4 inches of gravel in the bottom, leaves 20 inches to fill. That space comes to about 1.31 cubic feet. The post takes up about 0.14 cubic feet. The concrete fills the rest, about 1.2 cubic feet per fence post.

We estimate two bags of Sakrete concrete mix for each post, because two 80 pound bags yield 1.2 cubic feet. Double your post count to get the bags for the whole fence. A fence with 12 posts takes about 24 bags, or 1,920 pounds of mix. Treat the total as an estimate, because a hole that comes out a little wider or deeper takes more concrete. Mix each bag with the amount of water printed on it.

Gravel for the bottom of each post hole

Every post hole gets its 4 to 6 inches of gravel before the Sakrete concrete mix goes in. We stock four gravels, and you can see each one at the yard before you choose the base for your post holes. Give us your post count and the size of your holes, and we will work out the gravel you need at no charge.

Bag counts for a small slab at 4 inches thick

Sakrete gives a shortcut for a slab 4 inches deep. Multiply the square feet of the slab by 0.6, and the answer is the number of 80 pound bags. The shortcut already adds about 10 percent for waste, and the number it gives you is the number to buy. For a slab thicker than 4 inches, call us with the size, and we will work out the count with you.

Measure the length and the width of the slab in feet. If your tape gives you inches, divide each number by 12 to get feet. Multiply the two numbers in feet to get the square feet.

A 9 by 9 foot slab covers 81 square feet. Multiply 81 by 0.6 and you get 48.6. Round up, and you buy 49 bags of Sakrete concrete mix for that slab. Those 49 bags weigh 3,920 pounds together.

A patio in an L shape is two rectangles, and you measure each rectangle on its own. Say one part measures 10 by 12 feet and the other measures 4 by 6 feet. The two areas come to 120 and 24 square feet, for a total of 144 square feet. Multiply 144 by 0.6 and you get 86.4. Round up to 87 bags.

A walkway or a sidewalk poured 4 inches thick is a narrow slab, and the same shortcut works for it. A walkway 3 feet wide and 20 feet long covers 60 square feet. Multiply 60 by 0.6, and you buy 36 bags of Sakrete concrete mix.

The cubic yard math checks the shortcut. One cubic yard placed 4 inches deep covers 81 square feet, the same 9 by 9 foot slab. At 45 bags to the cubic yard, the shortcut adds 4 bags to the count for waste.

Sakrete rates the mix for foot traffic in 24 hours and for vehicle traffic in 72 hours. Keep foot traffic off the new slab for the first day. Give the slab three days before a car rolls onto it.

Bags and gravel from our Hot Springs Village yard

You find Sakrete concrete mix in the masonry supplies aisle, and we sell it by the bag. Our online store shows the stock and today's price. You buy the bags by calling the yard or coming in.

We are a 7-acre stone yard with Bennett Brothers of Hot Springs heritage since 1972. If your fence or patio needs stone as well, come see the actual stone and pick yours on the same visit.

We deliver straight to the jobsite for contractors, and we coordinate freight beyond the local area. For a job with footings and slabs across one site, total the cubic yards on your plans. Multiply that total by 45 for the count of 80 pound bags of Sakrete concrete mix. Call us with that number, and we will set up jobsite delivery. If your crew will lay block on a new footing, our guide to Type S mortar coverage helps you count the mortar for the wall.

Call 501-532-1905 with your post and slab sizes

Have these numbers ready when you call. With them in hand, we can work out the bag count with you on the phone.

• How many posts you are setting and how tall the fence will be
• The width of each post
• The length and width of each slab, in feet
• Whether you want jobsite delivery or a pickup at the yard

Call us at 501-532-1905, or come to 5643 N Hwy 7 in Hot Springs Village between 7:30 AM and 4:30 PM on a weekday. Bring your measurements, and we will count out the bags with you and show you the gravel for your post holes.