Surface grade and water direction
Paver Patio Slope Calculator
3 in of fall over 12 ft of horizontal run is a 2.08% slope (0.25 in per ft), directed away from the building. Enter your measurements below.
Sources checked
Your estimate
2.08 % grade
3 in fall over 12 ft horizontal distance; 0.25 in per ft.
- Measured fall1.19° surface angle3 in
- Fall per footExact ratio from your measurements0.25 in/ft
- At CMHA's 1.5% exampleComparison for this run, not a pass/fail test2.16 in fall
- At Unilock's 2% exampleComparison for this run, not a pass/fail test2.88 in fall
Grade alone cannot show local low spots, where runoff leaves the patio, or whether a drain is needed.
How to calculate paver patio slope
- Measure a horizontal run from the high edge to the low edge. The example is 12 ft, or 144 in.
- Measure vertical fall between those finished-surface elevations. The example is 3 in.
- Divide fall by horizontal run and multiply by 100: 3 ÷ 144 × 100 = 2.08%. Divide fall by feet to get 0.25 in per foot.
Choose the side where water is meant to go. Changing the direction changes the profile and the drainage warning, not the slope arithmetic. A single end-to-end grade does not reveal a low spot between the edges.
What the published paver slope guidance says
CMHA’s construction bulletin says pavement slopes should be at least 1.5%. Unilock’s advanced technical guide recommends at least 2% away from a house or building. These recommendations differ, and neither checks where runoff actually leaves your site. CMHA PAV-TEC-002-22, Construction of Interlocking Concrete Pavements; Unilock Advanced Tech Guide (2019)
Unilock describes its 2% figure as about ¼ in per foot. The two units are rounded equivalents: exactly 2% equals 0.24 in per foot; exactly ¼ in per foot is 2.08%. On the 12 ft example, they mean 2.88 in and 3 in of fall respectively.
- CMHA pavement slope
- 1.5% minimum in its construction bulletinCMHA PAV-TEC-002-22, Construction of Interlocking Concrete Pavements
- Unilock site drainage slope
- 2% recommended away from buildingsUnilock Advanced Tech Guide (2019)
How many inches of fall over a patio run?
| Horizontal run | At 1.5% | At 2% | At ¼ in per ft |
|---|---|---|---|
| 8 ft | 1.44 in | 1.92 in | 2 in |
| 12 ft | 2.16 in | 2.88 in | 3 in |
| 16 ft | 2.88 in | 3.84 in | 4 in |
| 20 ft | 3.6 in | 4.8 in | 5 in |
For the 12 ft example, the cited guides yield 2.16 in (CMHA pavement guidance) and 2.88 in (Unilock site drainage guidance). Measure the actual elevations and follow the specified profile for your project.
Where should the water go?
The grade needs a real low edge and a safe outlet. Away from a building is the usual direction in Unilock’s guidance; a patio that falls toward a building needs a designed interception and discharge route before water reaches the foundation. Unilock Advanced Tech Guide (2019)
This calculator does not size channel drains, determine soil infiltration, assess neighboring property runoff, or check accessibility and local grading requirements. For a large or complicated site, use surveyed elevations and a site drainage plan.
The paver patio planner counts the full material list. Use the paver base calculator for compacted gravel and the paver sand calculator for bedding once elevations and layer depths are set.
Paver patio slope questions
How do I calculate paver patio slope from a drop?
Divide the vertical drop in inches by the horizontal run in inches, then multiply by 100. A 3 in drop over 12 ft is 3 ÷ 144 × 100 = 2.08%. Measure the run horizontally, not along the sloping surface.
How much fall is 2% over 12 feet?
Two percent of 144 in is 2.88 in. Unilock also describes 2% as about 1/4 in per foot; exactly 1/4 in per foot gives 3 in over 12 ft, or 2.08%.
What slope should a paver patio have?
There is no single figure for every site. CMHA's pavement construction bulletin says at least 1.5%, while a Unilock site drainage guide recommends at least 2% away from buildings. The right grade also depends on where the water can go, access and local requirements.
Can the pavers slope toward the house?
A slope toward a building needs a designed way to intercept and discharge water before it reaches the foundation. This calculator only measures the surface grade; it does not size or approve a drain.
Does a 2% slope guarantee that a patio drains?
No. Low spots, uneven joints, blocked outlets and the surrounding ground can hold water even when the end-to-end grade is 2%. Check the actual finished surface and where runoff goes.
A planning aid, not an engineering calculation: your local code and building inspector have the final word. Terms