Concrete Slab Calculator
Enter the size of your patio, driveway or garage slab and get the concrete to buy, with every step shown. The example also works out the volume of a base layer under the slab. A slab that is not a rectangle can be drawn with Draw a shape.
A ready-made setup of the Concrete Calculator.
Estimates for planning, not professional advice. Read the full notice.
Shape
The drawing did not open. Length and width are still here.
Slab: shape and size
Skip the drawingDrag a round corner to move it. The small hollow diamond on a side is its curve handle: drag it across the side to curve the side (it is not a corner). To add a corner (a new point), tap the side itself, then choose Add a point here. Tapping a corner or a side opens its actions. Drag empty space to move the view; pinch, or Ctrl and the mouse wheel, to zoom. The keys are listed under Keys.
Keys
- Tab
- next corner; each says how far it is from corner 1
- Arrow keys on a corner
- move it one square; ten with Shift; 1/16 in with Alt
- Delete or Backspace
- remove the corner; its two sides join in one straight side
- + on a corner
- add a corner halfway along the next side
- Arrow keys on the drawing
- move the view; farther with Shift
- + and - on the drawing
- zoom in and out
- 0 on the drawing
- show the whole shape
- Ctrl+Z (Cmd+Z on a Mac)
- undo, except inside a typed field (it keeps its own)
- Ctrl+Shift+Z or Ctrl+Y
- redo
- Escape while dragging
- put it back where it was
- Enter on a corner or side
- go to its actions
- Escape in the actions
- close them and go back to the drawing
The drawing did not load. Check your connection and try again.
- Area
- 100 ft²
- Perimeter
- 40 ft
- Cut-out edges
No area until the shape is fixed.
Estimate for planning, from what you entered and the product data shown. Check product labels and your supplier before you buy.
Shape: Rectangle Change
Sides
Corners
Cut-outs
Feet and inches, like 12' 6"
Product names are trademarks of their owners. HoneyDoMath is not affiliated with, sponsored by or endorsed by these makers. Figures come from each maker's published sheets and are shown for information only.
Example: a patio slab
62 80 lb bags
- Concrete in the slab 33.33 ft³
- To order, with waste 1.36 yd³
- Base layer, in place 1.23 yd³
Your project
Enter a size to see your total.
Each product is rounded up once for the whole project, so the total can be less than the items bought alone added together. A line counted from a cut layout (sheets, boards or tiles laid out piece by piece) is counted for each item and added.
Shopping list
| Item | Size | Buy |
|---|---|---|
| Concrete mix | 80 lb bag | 62 |
Save on this device
Saved projects
No saved projects yet.
Worked example: a patio slab
Show the working
- Slab area 10 ft × 10 ft = 100 ft²
- Slab volume 100 ft² × 4 in = 33.33 ft³
- Add the waste allowance 33.333333 ft³ + 10%[1] = 36.67 ft³
- Divide by the bag's yield 36.666667 ft³ ÷ approx. 0.6 ft³[2] = 61.11 bags
- Round up once, to whole bags 61.11 bags = 62 × 80 lb bags
- Base layer volume, in place 100 ft² × 4 in = 33.33 ft³
Assumptions
The figures behind the example. Sourced figures link to their source below; a default is a starting value to check against your label or supplier.
| Assumption | Value | Details and changes |
|---|---|---|
| Concrete waste allowance | 10%[1] | |
| Default 10% is the top of NRMCA's 4% to 10% range. | ||
| Yield of the 40 lb bag | approx. 0.3 ft³[2] | |
| A 40 lb bag of QUIKRETE Concrete Mix 1101 yields about this many cubic feet, as the maker's own sheet states. | ||
| Yield of the 50 lb bag | approx. 0.375 ft³[2] | |
| A 50 lb bag of QUIKRETE Concrete Mix 1101 yields about this many cubic feet, as the maker's own sheet states. | ||
| Yield of the 60 lb bag | approx. 0.45 ft³[2] | |
| A 60 lb bag of QUIKRETE Concrete Mix 1101 yields about this many cubic feet, as the maker's own sheet states. | ||
| Yield of the 80 lb bag | approx. 0.6 ft³[2] | |
| An 80 lb bag of QUIKRETE Concrete Mix 1101 yields about this many cubic feet, as the maker's own sheet states. | ||
| Yield of the 90 lb bag | approx. 0.675 ft³[2] | |
| A 90 lb bag of QUIKRETE Concrete Mix 1101 yields about this many cubic feet, as the maker's own sheet states. | ||
Feet and inches, like 12' 6"
Slab jobs
Concrete volume, bags and base layer volume for common slab jobs
| Job (sizes) | Slab volume, without waste | To order, with waste | In 80 lb bags | Base layer, in place |
|---|---|---|---|---|
| Round patio, 10 ft across × 4 in | 26.18 ft³ | 1.07 yd³ | 48 × 80 lb bags | 26.18 ft³ |
| Slab, 12 ft 6 in × 9 ft 3 in × 4 in | 38.54 ft³ | 1.57 yd³ | 71 × 80 lb bags | 38.54 ft³ |
| Driveway, 12 ft × 24 ft × 5 in | 120 ft³ | 4.89 yd³ | 220 × 80 lb bags | 96 ft³ |
The waste allowance in the assumptions above is added once and the bags are rounded up once. The base layer column uses the base depth from the example and is a volume in place, with no waste allowance.
Yield per bag, by maker and mix
What one bag yields, for each concrete mix and bag size the calculator offers, as its maker states
| Mix and bag size | Yield per bag |
|---|---|
| QUIKRETE 5000 High Early Strength Concrete Mix, 50 lb | approx. 0.375 ft³ (per QUIKRETE's data sheet, checked Nov 12, 2026) |
| QUIKRETE 5000 High Early Strength Concrete Mix, 60 lb | approx. 0.45 ft³ (per QUIKRETE's data sheet, checked Nov 12, 2026) |
| QUIKRETE 5000 High Early Strength Concrete Mix, 80 lb | approx. 0.6 ft³ (per QUIKRETE's data sheet, checked Nov 12, 2026) |
| QUIKRETE Concrete Mix 1101, 40 lb | approx. 0.3 ft³ (per QUIKRETE's data sheet, checked Nov 12, 2026) |
| QUIKRETE Concrete Mix 1101, 50 lb | approx. 0.375 ft³ (per QUIKRETE's data sheet, checked Nov 12, 2026) |
| QUIKRETE Concrete Mix 1101, 60 lb | approx. 0.45 ft³ (per QUIKRETE's data sheet, checked Nov 12, 2026) |
| QUIKRETE Concrete Mix 1101, 80 lb | approx. 0.6 ft³ (per QUIKRETE's data sheet, checked Nov 12, 2026) |
| QUIKRETE Concrete Mix 1101, 90 lb | approx. 0.675 ft³ (per QUIKRETE's data sheet, checked Nov 12, 2026) |
| QUIKRETE Crack Resistant Concrete Mix, 50 lb | approx. 0.375 ft³ (per QUIKRETE's data sheet, checked Nov 12, 2026) |
| QUIKRETE Crack Resistant Concrete Mix, 60 lb | approx. 0.45 ft³ (per QUIKRETE's data sheet, checked Nov 12, 2026) |
| QUIKRETE Crack Resistant Concrete Mix, 80 lb | approx. 0.6 ft³ (per QUIKRETE's data sheet, checked Nov 12, 2026) |
| QUIKRETE Fast-Setting Concrete Mix 1004, 50 lb | approx. 0.375 ft³ (per QUIKRETE's data sheet, checked Nov 12, 2026) |
| QUIKRETE Fast-Setting Concrete Mix 1004, 60 lb | approx. 0.45 ft³ (per QUIKRETE's data sheet, checked Nov 12, 2026) |
| QUIKRETE Q•MAX PRO Concrete Mix, 50 lb | approx. 0.375 ft³ (per QUIKRETE's data sheet, checked Nov 12, 2026) |
| QUIKRETE Q•MAX PRO Concrete Mix, 80 lb | approx. 0.6 ft³ (per QUIKRETE's data sheet, checked Nov 12, 2026) |
| Rapid Set CONCRETE MIX, 60 lb | approx. 0.5 ft³ (per Rapid Set's published data, checked Nov 12, 2026) |
| SAKRETE 5000 Plus Concrete Mix, 50 lb | 0.38 ft³ (per SAKRETE's data sheet, checked Nov 12, 2026) |
| SAKRETE 5000 Plus Concrete Mix, 60 lb | 0.47 ft³ (per SAKRETE's data sheet, checked Nov 12, 2026) |
| SAKRETE 5000 Plus Concrete Mix, 80 lb | 0.6 ft³ (per SAKRETE's data sheet, checked Nov 12, 2026) |
| SAKRETE Crack-Resistant Concrete Mix, 50 lb | 0.38 ft³ (per SAKRETE's data sheet, checked Nov 12, 2026) |
| SAKRETE Crack-Resistant Concrete Mix, 80 lb | 0.6 ft³ (per SAKRETE's data sheet, checked Nov 12, 2026) |
| SAKRETE Fast Setting Concrete Mix, 50 lb | 0.38 ft³ (per SAKRETE's data sheet, checked Nov 12, 2026) |
| SAKRETE High Strength Concrete Mix, 40 lb | 0.3 ft³ (per SAKRETE's data sheet, checked Nov 12, 2026) |
| SAKRETE High Strength Concrete Mix, 60 lb | 0.45 ft³ (per SAKRETE's data sheet, checked Nov 12, 2026) |
| SAKRETE High Strength Concrete Mix, 80 lb | 0.6 ft³ (per SAKRETE's data sheet, checked Nov 12, 2026) |
| SAKRETE High Strength Concrete Mix, 90 lb | 0.66 ft³ (per SAKRETE's data sheet, checked Nov 12, 2026) |
| SAKRETE Maximizer Concrete Mix, 40 lb | 0.46 ft³ (per SAKRETE's data sheet, checked Nov 12, 2026) |
| SAKRETE Maximizer Concrete Mix, 80 lb | 0.92 ft³ (per SAKRETE's data sheet, checked Nov 12, 2026) |
| SAKRETE Pro-Mix Advanced Concrete Mix, 50 lb | 0.375 ft³ (per SAKRETE's data sheet, checked Nov 12, 2026) |
Product names are trademarks of their owners. HoneyDoMath is not affiliated with, sponsored by or endorsed by these makers. Figures come from each maker's published sheets and are shown for information only.
Sources: [3][2][4][5][6][7][8][9][10][11][12][13]
The list is in alphabetical order by maker, then by mix. Your bag's label comes first. If it says something different, use the label.
IRC values
Slab figures from the International Residential Code, with its section numbers
| Item | Model-code value |
|---|---|
| Minimum floor slab thickness (section R506.1) | 3.5 inModel-code (2021 IRC R506.1) minimum floor slab thickness; local adopted codes differ. |
| Vapor retarder under the slab, thickness (section R506.2.3) | 10 milModel-code (2021 IRC R506.2.3) minimum vapor retarder thickness under a slab; local adopted codes differ. |
| Vapor retarder under the slab, joint lap (section R506.2.3) | 6 inModel-code (2021 IRC R506.2.3) minimum lap of vapor retarder joints; not the wire-mesh lap. |
These are model-code values. The code your area has adopted may differ.
- The 2021 IRC, section R506.1, says “Floors shall be a minimum 3½ inches (89 mm) thick”
- The 2021 IRC, section R506.2.3, says “A minimum 10-mil (0.010 inch; 0.254 mm) vapor retarder conforming to ASTM E1745 Class A requirements with joints lapped not less than 6 inches (152 mm) shall be placed between the concrete floor slab and the base course or the prepared subgrade where a base course does not exist.”
Questions
How much concrete do I need for a slab?
Multiply the length, width and thickness to get the volume, add a waste allowance, and read the result in bags or cubic yards. The calculator shows every step for a slab of your size.
How thick should a concrete slab be?
The International Residential Code names a minimum floor slab thickness, shown in the IRC values table with the code's own wording. Your local code and your load decide what applies to your slab.
Does a slab need a vapor retarder?
The International Residential Code describes one under a floor slab, with a thickness and a lap at the joints, quoted in the IRC values table. Your building department decides what applies in your area.
What is the base layer under a slab?
It is a layer of compacted gravel or crushed stone that the slab sits on. The example and the slab jobs table on this page show its volume in place, from the slab's own footprint and an example depth. The calculator itself counts the concrete only.
Is the base layer part of the concrete count?
The base layer is gravel or stone, not concrete, so the concrete count here covers only the slab. The base layer volume is shown on its own line.
Local codes and amendments differ; your building department decides.
Sources (15)
-
CIP 31, Ordering Ready Mixed Concrete (opens in new tab), National Ready Mixed Concrete Association, 2000, 2016, 2023.
Standards or industry body.
“Quantity of concrete ordered should be 4% to 10% more than an estimate calculated from the plan dimensions to account for contingencies.”
Checked November 12, 2026. Figures and codes change; verify with the source. Back to where this is used (Source 1) -
QUIKRETE Concrete Mix No. 1101 data sheet (opens in new tab), The Quikrete Companies, Revised October 2022.
Manufacturer data.
“An 80 lb (36.2 kg) bag yields approximately 0.60 ft3 (17 L)”
“A 40 lb (18.1 kg) bag yields approximately 0.30 ft3 (8.5 L)”
“A 50 lb (22.6 kg) bag yields approximately 0.375 ft3 (10.6 L)”
“A 60 lb (27.2 kg) bag yields approximately 0.45 ft3 (12.7 L)”
“A 90 lb (40.8 kg) bag yields approximately 0.675 ft3 (19.1 L)”
Per QUIKRETE's data sheet, checked Nov 12, 2026. Figures and codes change; verify with the source. Back to where this is used (Source 2) -
QUIKRETE 5000 High Early Strength Concrete Mix No. 1007 data sheet (opens in new tab), The Quikrete Companies, Revised November 2022.
Manufacturer data.
“A 50 lb (22.6 kg) bag yields approximately 0.375 ft3 (10.6 L)”
“A 60 lb (27.2 kg) bag yields approximately 0.45 ft3 (12.7 L)”
“An 80 lb (36.2 kg) bag yields approximately 0.60 ft3 (17 L)”
Per QUIKRETE's data sheet, checked Nov 12, 2026. Figures and codes change; verify with the source. Back to where this is used (Source 3) -
QUIKRETE Crack Resistant Concrete Mix No. 1006 data sheet (opens in new tab), The Quikrete Companies, Revised December 2021.
Manufacturer data.
“A 50 lb (22.6 kg) bag yields approximately 0.375 ft3 (10.6 L)”
“A 60 lb (27.2 kg) bag yields approximately 0.45 ft3 (12.7 L)”
“An 80 lb (36.2 kg) bag yields approximately 0.60 ft3 (17 L)”
Per QUIKRETE's data sheet, checked Nov 12, 2026. Figures and codes change; verify with the source. Back to where this is used (Source 4) -
QUIKRETE Fast-Setting Concrete Mix No. 1004 data sheet (opens in new tab), The Quikrete Companies, Revised November 2025.
Manufacturer data.
“Each 50 lb (22.6 kg) bag yields approximately 0.375 cu ft (10.6 L)”
“Each 60 lb (27.2 kg) bag yields approximately 0.45 cu ft (12.7 L)”
Per QUIKRETE's data sheet, checked Nov 12, 2026. Figures and codes change; verify with the source. Back to where this is used (Source 5) -
QUIKRETE Q•MAX PRO Concrete Mix No. 1004-81 data sheet (opens in new tab), The Quikrete Companies, Revised April 2022.
Manufacturer data.
“A 50 lb (22.6 kg) bag and an 80 lb (36.2 kg) bag of QUIKRETE Q•MAX PRO Concrete Mix will yield approximately 0.375 ft3 (10.6 L) and 0.6 ft3 (16.9 L) respectively, at the recommended consistency.”
Per QUIKRETE's data sheet, checked Nov 12, 2026. Figures and codes change; verify with the source. Back to where this is used (Source 6) -
Rapid Set CONCRETE MIX datasheet DS_004_EN (opens in new tab), CTS Cement Manufacturing Corporation (Rapid Set), Datasheet DS_004_EN, web view, © 2026.
Manufacturer data.
“One 60-lb (27.2-kg) bag of CONCRETE MIX will yield approximately 0.5 ft3 (0.01 m3).”
Per Rapid Set's published data, checked Nov 12, 2026. Figures and codes change; verify with the source. Back to where this is used (Source 7) -
SAKRETE 5000 Plus Concrete Mix technical data sheet (opens in new tab), SAKRETE of North America, Technical data sheet, 2023 (sakrete.com copy).
Manufacturer data.
“50 lb 0.38 ft3 2.1 qts”
“60 lb 0.47 ft3 2.5 qts”
“80 lb 0.6 ft3 3.5 qts”
Per SAKRETE's data sheet, checked Nov 12, 2026. Figures and codes change; verify with the source. Back to where this is used (Source 8) -
SAKRETE Crack-Resistant Concrete Mix technical data sheet (opens in new tab), SAKRETE of North America, Technical data sheet, no date read (sakrete.com copy).
Manufacturer data.
“50 lb 22.7 kg 0.38 ft3 0.01 m3”
“80 lb 36.3 kg 0.6 ft3 0.017 m3”
Per SAKRETE's data sheet, checked Nov 12, 2026. Figures and codes change; verify with the source. Back to where this is used (Source 9) -
SAKRETE Fast Setting Concrete Mix technical data sheet (opens in new tab), SAKRETE of North America, Rev. 05/18.
Manufacturer data.
“50 lb (22.6 kg) 0.38 ft3 (.01 m3) 2.5 to 3 qts (2.4 - 2.9 L)”
Per SAKRETE's data sheet, checked Nov 12, 2026. Figures and codes change; verify with the source. Back to where this is used (Source 10) -
SAKRETE High Strength Concrete Mix technical data sheet (opens in new tab), SAKRETE of North America, Technical data sheet, 2023 (sakrete.com copy).
Manufacturer data.
“40 lb 0.30 ft3 1.75 qts”
“60 lb 0.45 ft3 2.5 qts”
“80 lb 0.6 ft3 3.5 qts”
“90 lb 0.66 ft3 4.25 qts”
Per SAKRETE's data sheet, checked Nov 12, 2026. Figures and codes change; verify with the source. Back to where this is used (Source 11) -
SAKRETE Maximizer Concrete Mix technical data sheet (opens in new tab), SAKRETE of North America, File name dated 04-24 (sakrete.com copy).
Manufacturer data.
“40 lb 18.1 kg 0.46 ft3 0.013 m3”
“80 lb 36.3 kg 0.92 ft3 0.026 m3”
Per SAKRETE's data sheet, checked Nov 12, 2026. Figures and codes change; verify with the source. Back to where this is used (Source 12) -
SAKRETE Pro-Mix Advanced Concrete Mix technical data sheet (opens in new tab), SAKRETE of North America, Technical data sheet, no date read (sakrete.com copy).
Manufacturer data.
“50 lb 22.7 kg 0.375 ft3 0.01 m3”
Per SAKRETE's data sheet, checked Nov 12, 2026. Figures and codes change; verify with the source. Back to where this is used (Source 13) -
2021 International Residential Code, Chapter 5 Floors (opens in new tab), International Code Council, 2021 IRC.
Code or government.
“Floors shall be a minimum 3½ inches (89 mm) thick”
“A minimum 10-mil (0.010 inch; 0.254 mm) vapor retarder conforming to ASTM E1745 Class A requirements with joints lapped not less than 6 inches (152 mm) shall be placed between the concrete floor slab and the base course or the prepared subgrade where a base course does not exist.”
Checked November 12, 2026. Figures and codes change; verify with the source. Back to where this is used (Source 14) -
CIP 29, Vapor Retarders Under Slabs on Grade (opens in new tab), National Ready Mixed Concrete Association, CIP 29 (sheet in 2021/01 upload folder).
Standards or industry body.
“A minimum thickness of 10 mils (0.25 mm) is recommended for reduced vapor transmission and for required durability during and after installation.”
“Vapor retarder sheets should be overlapped by 6 inches [150 mm] at the seams and taped and sealed around utility or column openings”
Checked November 12, 2026. Figures and codes change; verify with the source. Back to where this is used (Source 15)
These are summaries of what the sources say, not professional advice. Codes and product data change. Check with your building department and the product label about your own project.
Sources
- [1] National Ready Mixed Concrete Association, CIP 31, Ordering Ready Mixed Concrete. Checked November 12, 2026. https://www.nrmca.org/wp-content/uploads/2021/01/31pr.pdf
- [2] QUIKRETE, QUIKRETE Concrete Mix No. 1101 data sheet. Checked November 12, 2026. https://www.quikrete.com/PDFs/DATA_SHEET-Concrete%20Mix%201101.pdf
- [3] QUIKRETE, QUIKRETE 5000 High Early Strength Concrete Mix No. 1007 data sheet. Checked November 12, 2026. https://www.quikrete.com/PDFs/DATA_SHEET-QUIKRETE%205000%201007.pdf
- [4] QUIKRETE, QUIKRETE Crack Resistant Concrete Mix No. 1006 data sheet. Checked November 12, 2026. https://www.quikrete.com/PDFs/DATA_SHEET-Crack%20Resistant%20Concrete%20Mix%201006-80.pdf
- [5] QUIKRETE, QUIKRETE Fast-Setting Concrete Mix No. 1004 data sheet. Checked November 12, 2026. https://www.quikrete.com/PDFs/DATA_SHEET-Fast%20Setting%20Concrete%20Mix%201004-50.pdf
- [6] QUIKRETE, QUIKRETE Q•MAX PRO Concrete Mix No. 1004-81 data sheet. Checked November 12, 2026. https://www.quikrete.com/PDFs/DATA_SHEET-QMAX-PRO-1004-81.pdf
- [7] Rapid Set, Rapid Set CONCRETE MIX datasheet DS_004_EN. Checked November 12, 2026. https://www.ctscement.com/datasheet/CONCRETE_MIX_Datasheet_DS_004_EN
- [8] SAKRETE, SAKRETE 5000 Plus Concrete Mix technical data sheet. Checked November 12, 2026. https://www.sakrete.com/wp-content/uploads/2021/07/Sakrete-5000-Plus-TDS.pdf
- [9] SAKRETE, SAKRETE Crack-Resistant Concrete Mix technical data sheet. Checked November 12, 2026. https://www.sakrete.com/wp-content/uploads/2021/07/Sakrete-Crack-Resistant-Concrete-TDS.pdf
- [10] SAKRETE, SAKRETE Fast Setting Concrete Mix technical data sheet. Checked November 12, 2026. https://www.sakrete.com/wp-content/uploads/2021/07/Fast-Setting-Concrete.pdf
- [11] SAKRETE, SAKRETE High Strength Concrete Mix technical data sheet. Checked November 12, 2026. https://www.sakrete.com/wp-content/uploads/2024/01/Sakrete-High-Strength-Concrete-Mix-TDS.pdf
- [12] SAKRETE, SAKRETE Maximizer Concrete Mix technical data sheet. Checked November 12, 2026. https://www.sakrete.com/wp-content/uploads/2024/09/Sakrete-Maximizer-Concrete-Mix-TDS-04-24.pdf
- [13] SAKRETE, SAKRETE Pro-Mix Advanced Concrete Mix technical data sheet. Checked November 12, 2026. https://www.sakrete.com/wp-content/uploads/2023/02/Pro-Mix-Advanced-Concrete-Mix-TDS-1.pdf
- [14] International Code Council, 2021 International Residential Code, Chapter 5 Floors. Checked November 11, 2026. https://codes.iccsafe.org/content/IRC2021P2/chapter-5-floors
- [14] International Code Council, 2021 International Residential Code, Chapter 5 Floors. Checked November 12, 2026. https://codes.iccsafe.org/content/IRC2021P2/chapter-5-floors
- [15] National Ready Mixed Concrete Association, CIP 29, Vapor Retarders Under Slabs on Grade. Checked November 12, 2026. https://www.nrmca.org/wp-content/uploads/2021/01/29pr.pdf