How much concrete does a one-car parking pad take?

For a measured 10 by 20 foot pad at a supplied 4 inch thickness, the geometric volume is 66.67 cubic feet, 2.47 cubic yards or 1.89 cubic meters. A 10 percent allowance gives 2.72 cubic yards. At the example yields of 0.60, 0.45 and 0.30 cubic feet per bag, that total needs 123 bags of 80 lb, 163 of 60 lb or 245 of 40 lb. These dimensions and thickness are an arithmetic example; enter your own measured dimensions and specified thickness.

Why is the answer bigger than length times width times thickness?

The waste allowance is added on top of the geometric volume. For a rectangle, volume is length × width × supplied thickness, using one unit throughout. A 12 by 10 foot slab at 5 inches contains 50 cubic feet or 1.85 cubic yards. With 10 percent waste the total is 2.04 cubic yards, while 1.85 remains visible before waste. Type any allowance from 0 to 100 percent; 0%, 5% and 10% buttons are shortcuts, not a recommendation for your site.

Which bag does the bag count assume?

The approximate example yields are 0.30 cubic feet for 40 lb, 0.45 for 60 lb and 0.60 for 80 lb. These are mixed-concrete volumes, not conversions from bag weight. One cubic meter takes 118, 79 or 59 bags respectively before waste. Choose Custom and enter the yield printed on your bag in cubic feet, cubic yards, cubic meters or liters when it differs. The count divides total volume by that yield and rounds up to a whole bag.

Can this page tell me how thick a slab should be?

No, and it is built not to. Thickness is an input here: you type the thickness, the page reports the volume it implies, and nothing on the page prints a thickness, a rebar size or a mix strength. Choosing a thickness for a load, a vehicle or a footing is structural work, and a number we estimated is not something anyone should build on. Get the thickness from an engineer, your local building code or the person specifying the job, then come back and type it in.

Is anything uploaded?

The dimensions, bag yields and arithmetic stay in your browser. Browser storage remembers your editable worksheet after a change; it may be unavailable in private or blocked-storage mode. Opening defaults or the yard preset does not save a new preference. Clearing browser data removes the draft.

Can I mix feet and inches, or feet and metres?

Yes. A 12 foot length, 10 foot width and 5 inch thickness need no conversion first. The same measurements entered as 3.6576 meters, 3.048 meters and 127 millimeters give 50.00 cubic feet and 1.85 cubic yards before waste. Unit factors use their exact definitions; the arithmetic uses browser numbers and displayed values are rounded.

How do I calculate concrete for a round or triangular slab?

Choose Circle and enter the diameter and supplied thickness: volume is π × (diameter ÷ 2)² × thickness. A 12 foot diameter at 4 inches contains about 1.40 cubic yards before waste. Choose Triangle and enter the base and perpendicular height, plus thickness: volume is base × perpendicular height × thickness ÷ 2. A 12 foot base and 10 foot perpendicular height at 5 inches contain 25 cubic feet or 0.93 cubic yards before waste. A sloping side is not the perpendicular height.

Can I calculate a 10x10, 10x12, 20x20, 20x30 or 30x40 slab?

Yes. Select Rectangle, enter the two measured dimensions and then the supplied thickness. For example, 10 by 12 feet at 4 inches is 40 cubic feet or 1.48 cubic yards before waste; 20 by 30 feet at the same thickness is 200 cubic feet or 7.41 cubic yards. Length and width alone give area, so a thickness is still needed for concrete volume. The footprint is also shown in square feet, square yards and square meters. If you already know the square footage, choose Area to volume and enter the area and specified thickness directly.

Can this calculate footing, monolithic or thickened-edge concrete?

This is a flat-slab geometry model. It does not add varying-depth footings, thickened edges, grade beams, voids or profiled metal deck. It also does not design reinforcement, load capacity, strength or structural thickness. A supplier or project designer must specify those sections; their extra volume is not included in a single flat slab.

Does the calculator estimate concrete prices or a mix recipe?

It calculates measured volumes and bag counts. It does not provide supplier rates, installation or removal quotes, cement/sand/aggregate recipes or water ratios. Ready-mix volume and a known bag yield are different inputs from a concrete mix design. Current price and delivery terms come from the supplier.

Concrete Slab Calculator

Calculate a concrete slab's volume in cubic yards, cubic meters and cubic feet at once, with each dimension typed in the unit you actually measured it in. Feet, inches, yards, meters, centimeters and millimeters can be mixed freely across the fields. Choose a rectangle, circle or triangle, enter the specified thickness, and add a supplied waste allowance from 0 to 100 percent. The geometric volume stays beside the total. You can also enter a measured area and thickness, use a known volume to count bags, convert bags to volume, or find the area a supply covers at your thickness. Bag presets are approximate examples; Custom uses the mixed-concrete yield printed on your bag.

Volume with allowance10% allowance

Cubic yards2.04yd³1.56 m³ · 55.00 ft³ · 1.85 yd³ before waste

80 lb example bags92

Mix dimension units freely. Bag presets use approximate yields of 0.30, 0.45 and 0.60 ft³; choose Custom to use the mixed-concrete yield printed on your bag. Counts round up to whole bags.

How this is calculated

length × width × supplied thickness. 12 ft long × 10 ft wide × 5 in thick.

Slab footprint: 120.00 ft² · 11.15 m² · 13.33 yd².

Volume with allowance: 2.04 yd³ · 1.56 m³ · 55.00 ft³. Bag count = volume ÷ yield, rounded up: 92 at 16.9901 litres per bag.

12 ft x 10 ft x 5 inone-car pad, 10% waste
2.04 yd³ · 1.56 m³ · 92 bags
20 ft x 20 ft x 0.5 ftdouble garage, all in feet, no waste
7.41 yd³ · 5.66 m³ · 334 bags
3 m x 3 m x 100 mmmetric entry, 5% waste
1.24 yd³ · 0.95 m³ · 56 bags

Measured concrete geometry. Geometry uses exact unit definitions with browser-number arithmetic and rounded displays. Bag yields are approximate; use the yield on your bag. Thickness and waste are supplied inputs, not structural recommendations. This page does not calculate load capacity, reinforcement, mix design, supplier prices or installation costs. For varying-depth, thickened-edge, footing or monolithic work, this flat-slab model does not total those extra sections.

Common questions

How much concrete does a one-car parking pad take?: For a measured 10 by 20 foot pad at a supplied 4 inch thickness, the geometric volume is 66.67 cubic feet, 2.47 cubic yards or 1.89 cubic meters. A 10 percent allowance gives 2.72 cubic yards. At the example yields of 0.60, 0.45 and 0.30 cubic feet per bag, that total needs 123 bags of 80 lb, 163 of 60 lb or 245 of 40 lb. These dimensions and thickness are an arithmetic example; enter your own measured dimensions and specified thickness.
Why is the answer bigger than length times width times thickness?: The waste allowance is added on top of the geometric volume. For a rectangle, volume is length × width × supplied thickness, using one unit throughout. A 12 by 10 foot slab at 5 inches contains 50 cubic feet or 1.85 cubic yards. With 10 percent waste the total is 2.04 cubic yards, while 1.85 remains visible before waste. Type any allowance from 0 to 100 percent; 0%, 5% and 10% buttons are shortcuts, not a recommendation for your site.
Which bag does the bag count assume?: The approximate example yields are 0.30 cubic feet for 40 lb, 0.45 for 60 lb and 0.60 for 80 lb. These are mixed-concrete volumes, not conversions from bag weight. One cubic meter takes 118, 79 or 59 bags respectively before waste. Choose Custom and enter the yield printed on your bag in cubic feet, cubic yards, cubic meters or liters when it differs. The count divides total volume by that yield and rounds up to a whole bag.
Can this page tell me how thick a slab should be?: No, and it is built not to. Thickness is an input here: you type the thickness, the page reports the volume it implies, and nothing on the page prints a thickness, a rebar size or a mix strength. Choosing a thickness for a load, a vehicle or a footing is structural work, and a number we estimated is not something anyone should build on. Get the thickness from an engineer, your local building code or the person specifying the job, then come back and type it in.
Is anything uploaded?: The dimensions, bag yields and arithmetic stay in your browser. Browser storage remembers your editable worksheet after a change; it may be unavailable in private or blocked-storage mode. Opening defaults or the yard preset does not save a new preference. Clearing browser data removes the draft.
Can I mix feet and inches, or feet and metres?: Yes. A 12 foot length, 10 foot width and 5 inch thickness need no conversion first. The same measurements entered as 3.6576 meters, 3.048 meters and 127 millimeters give 50.00 cubic feet and 1.85 cubic yards before waste. Unit factors use their exact definitions; the arithmetic uses browser numbers and displayed values are rounded.
How do I calculate concrete for a round or triangular slab?: Choose Circle and enter the diameter and supplied thickness: volume is π × (diameter ÷ 2)² × thickness. A 12 foot diameter at 4 inches contains about 1.40 cubic yards before waste. Choose Triangle and enter the base and perpendicular height, plus thickness: volume is base × perpendicular height × thickness ÷ 2. A 12 foot base and 10 foot perpendicular height at 5 inches contain 25 cubic feet or 0.93 cubic yards before waste. A sloping side is not the perpendicular height.
Can I calculate a 10x10, 10x12, 20x20, 20x30 or 30x40 slab?: Yes. Select Rectangle, enter the two measured dimensions and then the supplied thickness. For example, 10 by 12 feet at 4 inches is 40 cubic feet or 1.48 cubic yards before waste; 20 by 30 feet at the same thickness is 200 cubic feet or 7.41 cubic yards. Length and width alone give area, so a thickness is still needed for concrete volume. The footprint is also shown in square feet, square yards and square meters. If you already know the square footage, choose Area to volume and enter the area and specified thickness directly.
Can this calculate footing, monolithic or thickened-edge concrete?: This is a flat-slab geometry model. It does not add varying-depth footings, thickened edges, grade beams, voids or profiled metal deck. It also does not design reinforcement, load capacity, strength or structural thickness. A supplier or project designer must specify those sections; their extra volume is not included in a single flat slab.
Does the calculator estimate concrete prices or a mix recipe?: It calculates measured volumes and bag counts. It does not provide supplier rates, installation or removal quotes, cement/sand/aggregate recipes or water ratios. Ready-mix volume and a known bag yield are different inputs from a concrete mix design. Current price and delivery terms come from the supplier.

Geometry uses exact unit definitions with browser-number arithmetic and rounded displays. Bag yields are approximate; use the yield on your bag. Thickness and waste are supplied inputs, not structural recommendations.