ConcreteCalsFree · No sign-up · US & metric units
Calculate concrete yards, bags, cost, and rebar for slabs, footings, columns, walls, curbs, and steps. Results update instantly as you type.
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Concrete & rebar guide
ConcreteCals is a free concrete and rebar calculator that turns any shape into an accurate material order. Enter the length, width, thickness or diameter of a slab, footing, wall, curb, column or set of steps, and the tool returns volume in cubic yards, cubic meters and cubic feet, bag counts for 50 lb, 60 lb and 80 lb mix, rebar length and weight, and a running cost estimate. Everything runs in your browser, so results update as you type and no dimensions leave your device.
Suppliers in the United States quote concrete in cubic yards, and the concrete calculator yards output is the number you will read over the phone. A 10 ft × 10 ft slab at 4 in thick works out to 1.23 cubic yards before waste. Add 5–10% for spillage, uneven subgrade and over-excavation — the waste slider applies it automatically — then round up to the nearest quarter or half yard, because plants batch in fixed increments. Getting the yardage right the first time is the simplest way to avoid a short pour and a second delivery fee.
For small projects, the concrete calculator bags section converts the same volume into 50 lb, 60 lb and 80 lb bags, so you can compare shelf prices before leaving the house. An 80 lb bag yields roughly 0.6 cubic feet, a 60 lb bag about 0.45 cubic feet, and a 50 lb bag around 0.37 cubic feet. Counts are rounded up, so you buy enough for the form rather than just the arithmetic. Mix only what you can place before it starts to set.
The rebar calculator uses the same dimensions as the concrete estimate. Switch on rebar reinforcement, then choose a bar size from #3 to #8 (or 10–20 mm), a spacing, an edge cover and whether the pour gets one layer or top and bottom layers. The tool counts bars in both directions, multiplies by cut length, adds your waste allowance for laps and offcuts, then converts the total to pounds and kilograms.
The core formula is simple: bars per direction = floor((span − 2 × cover) ÷ spacing) + 1. Multiply each count by its cut length, add the two directions, then multiply by the number of layers. Standard bar weights are #3 0.376 lb/ft, #4 0.668 lb/ft, #5 1.043 lb/ft, #6 1.502 lb/ft, #7 2.044 lb/ft and #8 2.670 lb/ft. A 10 ft × 10 ft slab with #4 bars at 12 in on center, 2 in cover and one layer needs about 193 ft before waste — roughly 213 ft, 142 lb or 11 × 20 ft bars once you add 10% for laps and cuts.
Cover is measured from the concrete edge to the nearest bar; 2 in is typical for slabs, footings and walls, while 1.5 in suits protected interior work. For curbs and steps the calculator switches to longitudinal bars only, spaced across the width. Rebar size and spacing are structural decisions — use this estimate for budgeting and confirm the final layout with a licensed engineer or your local building department.
Type a price per cubic yard and the tool becomes a concrete calculator cost estimate, showing the material total, the unit rate and the volume it was based on. Ready-mix usually runs $120–$180 per cubic yard depending on mix design, delivery distance and short-load charges, while bagged mix costs more per yard but makes sense below one cubic yard. Compare both figures before ordering, use the rebar calculator above for reinforcement, and budget separately for formwork, base gravel and finishing tools.
The ready mix concrete calculator is built for delivery orders. It adds the waste allowance, shows cubic yards and cubic meters side by side, and gives you the three numbers a dispatcher will ask for: total volume, pour thickness and the shape being filled. A standard truck carries 8–10 cubic yards, so the result also tells you whether you need a full load or a short load. Confirm the final figure with your plant, since batching rules and minimum charges vary by supplier.
Branded products work the same way. Use the concrete calculator as a Sakrete concrete calculator: read the 50 lb, 60 lb or 80 lb counts and match them to the yield printed on the bag. For deck posts and round footings, the Sonotube concrete calculator approach uses the tube diameter and height to find the volume inside the form, so you can plan bags or ready-mix for 8 in, 10 in or 12 in tubes without working through πr² by hand.
Metric projects are covered too. The concrete calculator UK workflow accepts metres and centimetres and shows cubic metres beside cubic yards, matching how UK suppliers quote. A 3 m × 2 m slab at 100 mm deep is 0.6 cubic metres, or about 0.78 cubic yards. Every field has its own unit selector, so you can mix feet, inches, metres and centimetres in one calculation and still get a consistent result.
Every figure is an estimate based on standard concrete density and standard rebar weights. For large pours, confirm the final volume, mix and price with your supplier before the truck is booked, and have a licensed engineer approve the reinforcement layout.
Three quick steps to get your concrete estimate.
Choose from slab, circle, footing, wall, curb, or steps. The form adapts instantly.
Type length, width, thickness, or other measurements in feet, inches, or counts, then optionally set the rebar size, spacing and cover.
See cubic yards, cubic meters, bag counts, rebar length and weight, and estimated cost immediately.
Answers to the most common questions about concrete volume, bags, yards, rebar quantities, gravel bases, formulas and slab quantities.
This concrete calculator needs three inputs for a slab: length, width and thickness. It multiplies them to find cubic feet, divides by 27 for cubic yards, adds your waste percentage, then converts the total into 50 lb, 60 lb and 80 lb bags plus a cost estimate. For round footings use diameter and height; for walls use length, height and thickness. Every field accepts feet, inches, metres or centimetres, so no manual conversion is needed.
Most slabs sit on a 4 in gravel base, or 6 in where vehicles park. Multiply the slab area by the base depth in feet, then divide by 27. A 10 ft × 10 ft slab with 4 in of gravel needs 100 × 0.333 = 33.3 cubic feet, or 1.23 cubic yards — roughly 1.7 tons of crushed stone. Add 5–10% for compaction and uneven subgrade.
Enter the volume, then read the 50 lb, 60 lb and 80 lb rows. An 80 lb bag yields about 0.6 cubic feet, a 60 lb bag about 0.45 cubic feet, and a 50 lb bag about 0.37 cubic feet. A 10 ft × 10 ft slab at 4 in thick is 33.3 cubic feet, so plan on 56–58 bags of 80 lb mix, rounded up. Always check the yield printed on the bag you buy.
Cubic yards = cubic feet ÷ 27. Measure length, width and thickness in feet (divide inches by 12), multiply them together, then divide by 27. A 10 ft × 10 ft slab at 4 in thick is 100 × 0.333 = 33.3 cubic feet, or 1.23 cubic yards. Add 5–10% waste, then round up to the quarter or half yard your supplier sells.
Slab: length × width × thickness. Footing: length × width × height. Wall: length × height × thickness. Cylinder: π × radius² × height. Steps: run × rise × width × number of steps. Keep every measurement in feet, then divide the cubic feet by 27 for cubic yards, or multiply cubic yards by 0.765 to get cubic metres. Add waste before you order.
30 ft × 40 ft = 1,200 square feet. At 4 in thick (0.333 ft) that is 400 cubic feet, or 14.81 cubic yards. Add 10% waste for a practical order of about 16.3 cubic yards. At $150 per cubic yard, expect roughly $2,220 before waste or $2,445 with it. Plan two truckloads, since a standard mixer carries 8–10 cubic yards; bagging it would take about 670–700 bags of 80 lb mix.
One cubic yard covers 27 square feet at 12 inches thick, 81 square feet at 4 inches thick, or 54 square feet at 6 inches thick. Divide your slab area by the coverage for its depth to estimate the yards you need.
On average, one cubic yard needs about 73–75 bags of 50 lb, 60–63 bags of 60 lb, or 45–47 bags of 80 lb concrete mix. Bag yields vary by brand, so check the yield printed on the bag before ordering.
Yes. Add 5–10% for spillage, uneven subgrade and over-excavation. The waste slider applies the allowance to every result and starts at 0%, so you decide the margin.
A 10 ft × 10 ft slab with #4 bars at 12 in on center, 2 in cover and one layer needs about 193 ft of rebar before waste. Add 10% for laps and cuts: roughly 213 ft, 142 lb, or 11 × 20 ft bars. Two layers double it. Confirm the bar size and spacing with your engineer or building plan before ordering.
Bars per direction = floor((span − 2 × cover) ÷ spacing) + 1. Multiply each count by its cut length, add both directions, then multiply by the number of layers. Apply a 5–10% waste allowance for laps and offcuts, then multiply total length by the bar weight. The rebar calculator above does this automatically for slabs, footings, walls, circles, curbs and steps.
Residential slabs commonly use #3 (3/8 in) or #4 (1/2 in) bars at 12–18 in on center. Driveways and slabs carrying vehicles often use #4 or #5 at 12 in on center. These are rules of thumb, not a structural design — follow the engineered plan or local building code for your project.
Number 4 rebar weighs 0.668 lb per foot, or about 13.4 lb per 20 ft bar. For comparison, #3 is 0.376 lb/ft, #5 is 1.043 lb/ft, #6 is 1.502 lb/ft, #7 is 2.044 lb/ft and #8 is 2.670 lb/ft. Metric bars weigh about 0.617 kg/m for 10 mm, 0.888 kg/m for 12 mm, 1.578 kg/m for 16 mm and 2.466 kg/m for 20 mm.
Standard concrete weighs about 4,050 lb per cubic yard, or 150 lb per cubic foot (roughly 2,400 kg per cubic metre).
Choose the circular shape and enter the tube diameter plus the pour height as the thickness. A 12 in tube filled 4 ft high comes to about 0.12 cubic yards, or six 80 lb bags before waste.
Sakrete yields differ by product. A 50 lb bag of general-purpose mix typically yields about 0.37 cubic feet and an 80 lb bag about 0.6 cubic feet. Enter your volume, compare the 50 lb and 80 lb rows, then match them to the yield printed on the bag.
Switch any dimension field to metres or centimetres and read the cubic metre value below the main result. The calculator also shows cubic feet, and one cubic metre equals about 1.308 cubic yards.
Ready-mix typically costs $120–$180 per cubic yard in the US, depending on mix design, delivery distance and short-load fees. Enter your supplier rate in the price field for a project total, then confirm delivery charges before ordering.