Concrete Patio Slope Calculator Guide
Plan concrete patio slope by fall per foot, drainage direction, door thresholds, forms, finish, and contractor quote questions.
A concrete patio slope calculator helps you translate drainage intent into a height difference across the slab. The goal is not only to calculate concrete volume. The patio also needs a drainage direction, form elevations, door threshold checks, finish plan, and quote scope.
Use the Concrete Patio Calculator Guide for yards and bags. Use the Concrete Patio Drainage Cost Guide when water already collects near the house. Then use the Concrete Quote Reviewer and Concrete Proposal Kit to keep slope and drainage responsibilities written into the estimate.
Competitor calculator pages commonly focus on slab quantity. This guide covers the field question that affects whether the patio drains correctly after the concrete is placed.
Quick answer
Concrete patio slope is usually planned as fall over distance:
total fall = patio run x slope per foot
Example:
12 ft run x 1/8 in per ft = 1.5 in total fall
12 ft run x 1/4 in per ft = 3.0 in total fall
Confirm the correct slope for your surface, finish, code, accessibility, door thresholds, and drainage path with a qualified local professional. Too little slope can hold water. Too much slope can feel uncomfortable and create edge, step, or trip issues.
Patio slope quick table
| Patio run | 1/8 in per ft | 3/16 in per ft | 1/4 in per ft |
|---|---|---|---|
| 8 ft | 1.0 in fall | 1.5 in fall | 2.0 in fall |
| 10 ft | 1.25 in fall | 1.875 in fall | 2.5 in fall |
| 12 ft | 1.5 in fall | 2.25 in fall | 3.0 in fall |
| 16 ft | 2.0 in fall | 3.0 in fall | 4.0 in fall |
| 20 ft | 2.5 in fall | 3.75 in fall | 5.0 in fall |
The table is a planning aid, not a design rule. The right slope depends on where the water goes, what the patio connects to, and how the surface will be used.
Slope inputs to collect
| Input | Why it matters | Quote question |
|---|---|---|
| Drainage direction | Water should move away from the house. | Which way will the finished surface drain? |
| Patio run | Fall is based on distance. | What is the longest drainage run? |
| Door threshold | Slab must not trap water at doors. | What finished elevation is planned at the house? |
| Adjacent grade | Low yard edges can back water up. | Is grading included outside the patio edge? |
| Finish type | Stamped or textured surfaces drain differently. | Does finish choice change slope or drainage? |
| Forms | Form heights create the slope. | Are form elevations included in the quote? |
| Joints | Water can follow joints and edges. | How are control and isolation joints planned? |
If a quote includes patio drainage or grading, compare the same scope in the Concrete Patio Drainage Cost Guide.
Example: 12 ft patio away from the house
Assume a patio drains 12 ft from the house to the yard.
| Planning slope | Total fall | What it means |
|---|---|---|
| 1/8 in per ft | 1.5 in | Gentle slope, but drainage must be checked. |
| 3/16 in per ft | 2.25 in | Middle planning case for comparison. |
| 1/4 in per ft | 3.0 in | More noticeable fall across the patio. |
If the house-side edge is set too low, water may move toward the building. If the outside edge is too low for the yard grade, the patio may drain into a low spot. The calculator only gives fall; the site still needs an outlet.
Quote red flags
| Red flag | Follow-up question |
|---|---|
| No drainage direction | Which way does the finished patio drain? |
| No form elevation note | How are the high and low edges set? |
| No door threshold check | How is water kept away from doors and siding? |
| No grading scope | Who handles soil and lawn transitions? |
| No joint plan | Where will control and isolation joints go? |
| No drainage exclusion | Are drains, swales, or downspout changes included? |
Put slope and drainage notes into the bid before the pour. It is much easier to review a written scope than to argue after water stands on the patio.
FAQ
How do I calculate concrete patio slope?
Multiply the patio run by the planned fall per foot. For example, 12 ft at 1/8 in per ft equals 1.5 in of total fall.
Does patio slope change concrete volume?
For most simple patios, the volume change is usually small compared with the overall slab estimate. The bigger issue is form elevation, drainage, and finish quality.
Should a patio slope away from the house?
In many cases, yes, but site conditions, doors, drains, adjacent grade, and local requirements matter. Confirm the drainage plan with a qualified local professional.
Is slope included in a patio contractor quote?
Only if written. Ask for drainage direction, form elevations, grading scope, and exclusions.
Can a flat patio hold water?
Yes. A patio that is too flat, uneven, or poorly finished can pond water even when the volume calculation is correct.
Next step
Calculate patio quantity first, then enter contractor bids into the Concrete Quote Reviewer and verify that slope, drainage, grading, and finish are included.
Quote planning next step
Turn this guide into a concrete buying check
Run the matching calculator, then compare ready-mix, bagged concrete, delivery fees, access needs, and quote gaps before you buy materials or approve a contractor number.