Concrete patio calculator
A 12 m² patio poured 10 cm thick is 1.2 m³ of concrete, 1.32 m³ with the default 10% waste, or 88 bags at the default yield. Enter the area and thickness to get the volume and the bags to buy. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Area
- 12
- Thickness
- 0.1
- Waste percent
- 10
- Waste factor
- 1.1
- Volume
- 1.2
- Waste volume
- 0.12
Planning a backyard patio pour starts with a trustworthy concrete volume, not a rough mental estimate from a paced-off sketch. This concrete patio calculator multiplies your measured plan area by slab thickness to produce the bare rectangular-prism volume, then applies a waste allowance so you order enough mix for spillage, edge forms, and uneven subbase. It divides the waste-adjusted volume by bag yield to estimate whole bags to buy, or leaves you with cubic volume for a ready-mix quote. You keep one unit system end to end—square metres with thickness in metres, or square feet with thickness in feet—and optionally override waste percent and bag volume when your crew or supplier uses different numbers. Use the result for bagged DIY patio pours, truck-order checks, and multi-pad schedules where every patio has its own footprint and depth.
How patio volume, waste, and bag count are computed
Start from the plan-area identity used on patio and pad estimators: bare volume equals plan area times slab thickness, with area in square units and thickness in the matching linear unit so the product is a consistent cubic unit. Write volume equals A times T. If you measured a ten-centimetre patio slab, enter thickness as zero point one metres when area is in square metres; if you measured four inches, convert to feet before multiplying when area is in square feet.
Waste allowance is a percent of that bare volume: waste factor equals one plus waste percent over one hundred, waste volume equals bare volume times waste percent over one hundred, and volume with waste equals bare volume times the waste factor. Typical patio pours use about ten percent overage for spillage, form edge loss, and subbase variation; the calculator defaults waste percent to ten when you omit it, and you can set zero for a bare theoretical volume or twenty for a difficult site.
Bag estimate divides volume with waste by bag volume, the cubic yield printed or implied on the product—for example about zero point zero one five cubic metres for a typical twenty-five kilogram bag, or about zero point six cubic feet for a common eighty-pound bag. bags exact is the real quotient; bags is the ceiling of that quotient because shops sell whole bags. spare volume is how much extra yield the rounded bag count covers beyond the waste-inflated volume.
When bag volume is omitted the calculator uses the documented default of zero point zero one five cubic units and sets bag volume defaulted true. Area and thickness must both be strictly positive; waste percent when provided must lie between zero and one hundred inclusive; bag volume when provided must be strictly positive.
What you send and what you get back
Send two required finite numbers: area for the patio plan footprint in square units, and thickness for slab depth in matching linear units. Optionally send waste percent as a number from zero to one hundred; if you omit it the default ten percent applies and waste percent defaulted is true. Optionally send bag volume as the cubic yield of one bag in matching cubic units; if you omit it the default zero point zero one five applies and bag volume defaulted is true.
Missing required fields, non-numeric strings, NaN, and Infinity fail with invalid input and are not charged. Waste outside zero to one hundred and non-positive bag volume fail the same way. A classic check is twelve square metres at zero point one metre thickness with default waste and bag volume: bare volume is one point two cubic metres, volume with waste is one point three two, bags exact is eighty-eight, and bags is eighty-eight.
Another useful check is one hundred twenty square feet at zero point three three three feet thickness with ten percent waste and bag volume zero point six: bare volume is about thirty-nine point nine six cubic feet, waste inflates it, and bags ceilings to the next whole sack.
What you can do with it
DIY backyard patio shopping list
Enter measured plan area and slab thickness, keep or adjust the waste percent, set your bag yield if needed, and buy whole bags without shortfall or bulk overstock.
Hardscape multi-patio estimates
Feed each patio’s plan area and thickness into the same formula so purchase orders match the estimate and every waste and ceil step is auditable.
Ready-mix quote cross-check
Compute waste-adjusted patio volume from the plan first, then compare bags or convert volume to the unit your ready-mix supplier quotes.
FAQ
What happens if area or thickness is zero or negative?
Area and thickness must both be strictly positive; a non-positive value would make volume non-physical or zero.
What is the default waste percent and bag volume?
Bag volume defaults to 0.015 cubic units (roughly a typical 25 kg bag in m³). Override either field for your site and product yield.
What does it cost?
The browser tool is free and runs locally.
How do I enter a 4 inch or 10 cm slab thickness?
Use the linear unit that matches your area. With the area in square metres, 10 cm is 0.1 m; with the area in square feet, 4 inches is about 0.333 ft. Mixing units gives a volume that means nothing.
Can I use the result for a ready-mix truck order?
Yes. The volume with waste is in cubic units, so you can compare it directly with a truck quote instead of buying bags. Many people run the bag estimate first and then check it against the truck price.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/home/concrete-patio \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"area":12,"thickness":0.1}'const res = await fetch("https://api.kit.forhosting.com/home/concrete-patio", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"area": 12,
"thickness": 0.1
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/home/concrete-patio",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"area": 12,
"thickness": 0.1
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/home/concrete-patio", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"area":12,"thickness":0.1}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"area":12,"thickness":0.1}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/home/concrete-patio", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"area": 12,
"thickness": 0.1
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "home.concrete_patio",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
The same pure function powers the free browser tool and the paid API, so a phone quote matches the line item a script posts later. Zero or negative area or thickness is rejected with a clear invalid_input message instead of a silent nonsense volume.
How patio volume, waste, and bag count are computed
The pipeline is deterministic floating-point arithmetic with no random seeds, no wall-clock timestamps, and no network calls, so identical inputs always produce identical JSON.
What you send and what you get back
When area or thickness is zero or negative the request fails with a message that the dimension must be positive, so clients can correct the measurement before retrying. On success the response echoes cleaned area, thickness, and waste percent, flags for defaults, waste factor, bare volume, waste volume, volume with waste, the bag volume used, bags exact, integer bags, spare volume, a unit note reminder to keep one unit system, and a short formula string for documentation. Pricing for successful API calls is the published base of $0.002 per item; validation failures do not consume prepaid balance.
Where a concrete patio calculator shows up in real work
Homeowners pouring a backyard patio, seating pad, or outdoor kitchen base need a trustworthy bag count before a hardware-store run, especially when large bags are heavy and hard to return once opened. Ready-mix customers often convert a bagged estimate into cubic yards or cubic metres to compare against a truck quote, and having volume with waste explicit next to bags makes that conversion a transparent second step rather than a black-box guess. If you later need length-by-width rectangular slabs without a waste field, circular pads, stepped footings, rebar spacing grids, or mix design by compressive strength, treat those as separate search intents and landings rather than overloading this concrete patio volume and bag calculator page. Landscape and hardscape crews build patio schedules from measured or CAD plan areas and design thicknesses; a single deterministic endpoint that applies waste then ceilings bags reduces spreadsheet drift between the estimator and the purchasing clerk. Property managers planning multiple amenity pads feed each area-thickness pair through the API and attach bags to purchase orders so overstock stays intentional. Because this capability is a pure parse engine, API pricing is the published base of $0.002 per successful item and failed validation does not consume balance.
Technical questions
How does this concrete patio calculator work?
It multiplies area × thickness for bare volume, multiplies by (1 + waste_percent/100) for volume with waste, divides by bag_volume for an exact bag count, then ceilings to whole bags. Optional waste_percent defaults to 10; optional bag_volume defaults to 0.015 cubic units.
Which units should I use?
Any consistent set: m² with thickness in m and bag_volume in m³, or ft² with thickness in ft and bag_volume in ft³. Do not mix systems. The response includes a unit_note; it does not convert units for you.