Introduction
Figuring out how much concrete you need for a project can be tricky. If you order too little, you'll have to stop work and wait for more. If you order too much, you waste money on material you can't use. This concrete calculator gives you exact volume, weight, and bag counts for seven common project types: slabs, walls, columns, round footings, circular slabs, tubes, curbs and gutters, stairs, post holes, and footings.
Just enter your measurements, like length, width, and thickness, and the tool calculates the results. It converts between imperial and metric units, so you can work in feet, inches, meters, or centimeters. Every result includes a 10% waste factor built in, which accounts for spillage, uneven ground, and other real-world conditions that always use more concrete than the bare math suggests. The calculator also tells you how many pre-mixed bags you need in sizes ranging from 40 to 90 pounds, making it easy to plan a trip to the supply store.1
For a backyard patio, fence posts, concrete steps, or a foundation footing, this tool helps you estimate your concrete materials quickly and accurately before you start mixing or placing an order for ready-mix delivery.
How to Use Our Concrete Calculator
Enter the dimensions of your concrete project below, and this calculator will tell you how much concrete you need in volume, weight, and number of pre-mixed bags. It covers seven common shape types used in construction.
Unit System and Display: Choose between Imperial (feet, inches, yards) or Metric (meters, centimeters) for your input units and display results. The calculator will convert everything for you.
Slab, Square Footing, or Wall: Enter the length, width, and thickness (or depth) of your slab, square footing, or wall. A standard concrete slab is 4 inches thick. For a wall, enter the wall height as the thickness. Set the quantity if you have more than one identical pour.
Hole, Column, or Round Footing: Enter the diameter and the depth or height of your round column, hole, or circular footing. Use the quantity field if you are pouring more than one.
Circular Slab or Tube (Hollow Cylinder): Enter the outer diameter, inner diameter, and the height or depth of the tube or ring-shaped slab. The calculator finds the volume of concrete between the two diameters. Set the quantity if you need more than one.
Curb and Gutter: Enter the curb depth, gutter width, curb height, flag thickness, and total length of your curb and gutter section. Use the diagram on screen to see which measurement goes where. Set the quantity for multiple identical sections.
Stairs: Enter the run (tread depth), rise (height per step), width of the staircase, platform depth, and the number of steps. The calculator figures out the full solid volume of the staircase, including the filled area beneath each step. Set the quantity if you are building more than one staircase.
Post Holes: Enter the hole depth and the number of post holes you need to fill. The calculator automatically shows results for four common post and hole size combinations: 2-inch post with 6-inch hole, 3-inch post with 9-inch hole, 4-inch post with 12-inch hole, and 6-inch post with 18-inch hole. It subtracts the space taken up by the post itself.
Footing: Enter the depth, width, and length of your footing. This works for continuous strip footings used under walls or foundations. Set the quantity if you have more than one footing to pour.
Results: Each section shows the total concrete volume, estimated weight, and the number of pre-mixed bags needed in five common sizes (40 lb, 50 lb, 60 lb, 80 lb, and 90 lb). All bag estimates include an extra 10% for waste. A bar chart at the bottom compares the volume across all sections so you can see your full project at a glance.
How to Calculate Concrete for Your Project
Concrete is one of the most widely used building materials in the world. It is a mix of cement, water, sand, and gravel that hardens into a strong, durable surface. For a driveway, fence posts, or a foundation, knowing how much concrete you need is one of the most important steps in planning your project. Ordering too little means delays and extra trips to the store. Ordering too much means wasted money and leftover material you cannot use.
How Concrete Volume Is Measured
Concrete is measured by volume, most often in cubic yards (yd³) in the United States or cubic meters (m³) in countries that use the metric system. To find the volume, you multiply the length, width, and thickness (or depth) of the area you want to fill. For round shapes like columns or post holes, the formula uses the radius and the mathematical constant pi (π). The basic formulas are:
- Rectangular shapes (slabs, walls, footings): Length × Width × Depth
- Cylindrical shapes (columns, round footings): π × Radius² × Height
- Hollow cylinders (tubes, post holes): π × (Outer Radius² − Inner Radius²) × Height
Common Concrete Projects and Typical Dimensions
A standard concrete slab, like a patio or garage floor, is usually 4 inches thick. The International Residential Code sets a minimum of 3½ inches for concrete floors on the ground.3 Driveways are often 5 to 6 inches thick because they carry heavier loads. Sidewalks are typically 4 inches thick and 3 to 5 feet wide. Under the International Residential Code, house footings must be at least 12 inches wide and 6 inches thick, and sit at least 12 inches below undisturbed ground.2
Post holes for fences and deck supports follow a simple rule: Quikrete's directions make the hole about 3 times the post's width across and 1/3 of the post's overall length deep.1 So a 4-inch post needs a 12-inch hole, and an 8-foot post goes about 32 inches into the ground.
Why You Should Always Add Extra
The National Ready Mixed Concrete Association advises ordering 4% to 10% more concrete than the volume worked out from plan dimensions.4 This extra amount covers small spills, uneven ground, and the concrete that sticks to the inside of mixing equipment. Scattered, stop-and-start pours need a bigger allowance.4 Running short during a pour is a serious problem because concrete begins to set quickly, and a cold joint (where fresh concrete meets partially hardened concrete) creates a weak spot.
Pre-Mixed Bags vs. Ready-Mix Delivery
For small projects, pre-mixed bags from a hardware store are the easiest option. They come in common sizes: 40 lb, 50 lb, 60 lb, 80 lb, and 90 lb.1 Each bag yields a specific amount of concrete when mixed with water. For example, an 80 lb bag makes about 0.6 cubic feet of concrete.1 That is about 0.022 cubic yards. For anything larger than about 1 cubic yard, it usually makes more sense to order ready-mix concrete delivered by a truck. It saves time, gives a more consistent mix, and often costs less per cubic yard than buying dozens of bags.
Concrete Weight
Normal-weight concrete weighs about 140 to 150 pounds per cubic foot, or 2,240 to 2,400 kilograms per cubic meter.5 The calculator uses 150 pounds per cubic foot. This means even a small 4-inch thick, 10×10-foot slab weighs around 5,000 pounds. Knowing the weight helps you plan for structural support and figure out how many loads your vehicle can carry if you are picking up bags yourself.
Tips for a Successful Concrete Pour
- Prepare the ground first. Remove soft soil, add a compacted gravel base, and set your forms securely before mixing any concrete.
- Check the weather. Avoid pouring when temperatures are below 40°F (4°C) or above 90°F (32°C).6 Extreme temperatures cause curing problems.
- Don't add too much water. Extra water makes concrete easier to pour but weaker when it cures.7 Follow the mixing directions on the bag.
- Cure properly. Keep freshly poured concrete moist while it cures, typically for 3 to 7 days.8 Cover it with plastic sheeting or spray it with water to prevent cracking.
- Reinforce when needed. For slabs and footings that need extra strength, use rebar reinforcement.
Getting the right amount of concrete before you start saves time, money, and frustration. Use the calculator above to enter your project's exact dimensions, and it will work out the totals, including the 10% waste factor and bag counts, so you can focus on the actual work.