Plan the pour, not the guesswork
Concrete Calculator
Estimate slab volume, bag quantities, and material weight, or size a durable concrete footing for fence posts.
Bag counts are rounded up to whole bags. Fence-post results use a 6-inch gravel base below the set post; concrete volume excludes that gravel layer and subtracts the post displacement. Always verify local code, soil, wind, and product yield requirements.
How to use the Concrete Calculator
Choose Slab for a rectangular pour, then enter its length, width, and finished depth. Choose Fence Post to enter the finished fence height, number of posts, post type, and local frost line. In either mode, enter the concrete bag weight and optionally enter available vehicle payload to estimate the number of trips.
Bag quantities are rounded up because concrete mix is sold in whole bags. Weight results can help with delivery and vehicle load planning.
How are concrete and fence-post depth calculated?
Slabs: The calculator converts the entered depth from inches to feet, multiplies length × width × depth, and converts cubic feet to cubic yards. Bag estimates divide that volume by the selected bag yield and round up to the next whole bag.
Fence posts: The structural baseline is depth = (½ × finished fence height) − 6 inches, limited to a 24-inch minimum and a 48-inch maximum. This wood-post rule is found in official specifications based on ASTM F537. The calculator then compares that result with the local frost line plus 6 inches and uses whichever depth is greater.
Frost Line Reference
Northern US: 36–48" | Central US: 24–36" | Southern US: 12–24". Check local codes for exact requirements.
For chain-link post selections, the estimate assumes the steel post is set in concrete. ASTM F567 covers chain-link fence installation, including post setting, but it should not be read as the source of the wood-post depth equation above. The calculator uses the selected post dimensions to estimate a cylindrical hole, then subtracts the volume displaced by the buried post.
Structural post depth = (fence height ÷ 2) − 6 in, minimum 24 in, maximum 48 in
Set depth = deeper of structural depth or frost line + 6 in
Concrete per post = cylindrical hole volume − buried post volume
Total post concrete = concrete per post × number of posts
Bags per trip = whole bags that fit within available payload
Trips = bags needed ÷ bags per trip, rounded up
Loose or sandy soil: The calculator does not automatically adjust for soil type. Such conditions can require a deeper and wider footing; move up at least one practical hole size and confirm the final dimensions with local code, the fence manufacturer, or a qualified professional. Soil, wind exposure, gates, corners, privacy slats, and frost can all increase footing requirements.
Bag yield is estimated at 0.0075 cubic feet per pound, equivalent to 0.45 cubic feet for a 60 lb bag or 0.60 cubic feet for an 80 lb bag. The selected bag weight is used to estimate yield and total dry mix weight. When payload is greater than zero, trip estimates divide available vehicle payload by bag weight, round down to whole bags per trip, then round the required number of trips up. A payload of 0 skips the trip estimate. Confirm the yield printed on your product and never exceed the vehicle manufacturer's payload rating.
Frequently Asked Questions
How deep should a fence post be?
The calculator uses half the finished fence height minus 6 inches, with a 24-inch minimum and 48-inch structural maximum, then goes deeper when needed to reach 6 inches below the local frost line.
How many concrete bags are in one cubic yard?
One cubic yard is about 60 standard 60 lb bags or 45 standard 80 lb bags, based on the yields used by this calculator.
Should I order extra concrete?
Many projects add 5% to 10% for uneven excavation, spillage, and measurement variation. This calculator reports the measured volume without an automatic waste factor.
Does the weight include water?
No. Bag weights represent dry concrete mix. Water added during mixing increases the working weight.
