What slope is recommended immediately away from a foundation?

A common rule of thumb is at least 6 inches of fall over the first 10 feet away from the foundation, which is roughly a 5% slope. Some codes or local practices may specify slightly different values, so always check regional guidance and consider soil conditions.

Is 1% slope enough for patios and sidewalks?

Many patios and sidewalks are built between about 1% and 2% slope (roughly 1/8–1/4 inch per foot). Around 1% can work if the surface is smooth and well‑drained; if you regularly see puddles, you may need a bit more slope or additional drainage features.

Does soil type or surface material affect the slope I should use?

Yes. Clay soils and tight surfaces shed water more quickly and may need more attention to drainage, while sandy or well‑draining soils can handle gentle slopes better. This calculator only reports geometric slope, so combine its output with knowledge of your soil, surface material, and climate.

How do I measure slope accurately on site?

A simple method is to use a string line and a small bubble level. Stretch the string from the high point to the low point, level the string, and measure the vertical distance from the string down to the surface at the low end. That drop, along with the horizontal distance between stakes, gives you the inputs for this calculator.

Can I use metric measurements with this drainage slope calculator?

The inputs are in feet and inches because those units match most North American building and landscape guidance. You can still use metric by converting meters to feet and centimeters to inches before entering values, then interpret the slope outputs (percent and inches per foot) against typical design recommendations.

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Drainage Slope Calculator

Convert rise/run to slope % and inches-per-foot for driveways, patios, and yard drainage.

Results

Slope (%): 5.00
Inches drop per foot: 0.60

Overview

Proper drainage slope keeps water flowing away from your house, driveway, or patio instead of pooling where it can cause cracks, ice, or basement leaks. This drainage slope calculator converts simple rise‑over‑run measurements into slope percentage and inches of drop per foot so you can quickly check whether your grade is in a safe, code‑friendly range.

How to use this calculator

Measure the horizontal run of the surface using a tape measure, then enter that distance in feet. For longer runs, you can measure in sections and add them together.
Measure how much the surface drops vertically from the high point to the low point over that run and enter that value in inches.
The calculator converts those measurements into slope percentage and inches of drop per foot, using standard rise‑over‑run formulas.
Compare your results to common guidelines for driveways, patios, sidewalks, and yard grading to see whether you need to adjust your slope.
If you regrade, re‑measure and rerun the calculator until the outputs match your target slope range.

Inputs explained

Horizontal run (feet): The straight‑line horizontal distance between the high point and low point of the surface you are grading, measured in feet. This is the "run" in rise‑over‑run calculations.
Vertical drop (inches): How far the surface falls vertically over the measured run, in inches. This is the "rise" (or fall) in the slope ratio and is what drives water to flow downhill.

Outputs explained

Slope (%): The grade expressed as a percentage. A 2% slope means the surface drops 2 units vertically for every 100 units horizontally. Many patios and sidewalks are designed in the 1–2% range.
Inches drop per foot: The grade expressed as inches of drop per foot of run. For example, 0.25 in/ft is about a 2% slope. Contractors often think in these terms when setting forms or screeding concrete.

How it works

Slope is just the ratio between vertical drop and horizontal run. In grade work, that ratio is often expressed either as a percentage or as inches of drop per foot of run.

To get slope percentage, we first convert your horizontal run from feet to inches so the units match your vertical drop. Slope % = (drop in inches ÷ (run in feet × 12)) × 100.

To get inches per foot, we divide the total drop in inches by the run in feet: Inches per foot = drop (in) ÷ run (ft). A result of 0.25 means you drop a quarter inch every foot.

These two values describe the same grade in different ways. For example, about 1/4 inch per foot corresponds to roughly a 2% slope, while 1/8 inch per foot is around 1%.

By turning raw tape‑measure readings into these common slope formats, you can compare your project against typical recommendations from builders, manufacturers, and local codes.

Formula

Let run_ft be the horizontal run in feet and drop_in the vertical drop in inches.\n\n• Slope % = [drop_in ÷ (run_ft × 12)] × 100\n• Inches per foot = drop_in ÷ run_ft\n\nBoth values describe the same slope using different units commonly used in grading and drainage work.

When to use it

Checking that soil immediately around a foundation slopes away from the house to help keep basements and crawl spaces dry.
Verifying that a new patio, sidewalk, or driveway has enough slope for water to run off without creating puddles or ice sheets.
Planning yard regrading projects so you can add just enough fall to move water toward a swale, drain, or daylight outlet.
Laying out trench drains, French drains, or perforated pipe runs and confirming that they maintain a consistent fall toward the outlet.
Evaluating whether an existing slope is too steep and prone to erosion, ruts, or slippery conditions, especially on unpaved surfaces.

Tips & cautions

As a rough rule of thumb, many hardscape surfaces perform well with 1–2% slope (about 1/8–1/4 inch per foot), while the first 10 feet away from a foundation are often graded closer to 5% slope for aggressive drainage.
Avoid overly steep slopes on bare soil; high grades can accelerate erosion and washouts. If you must use a steep slope, consider erosion‑control matting, vegetation, or retaining structures.
Use a string line and line level or a laser level in the field: stretch the string level from the high point, level it, then measure the drop at the low point. That gives you the numbers to plug into this calculator.
Check local codes and manufacturer installation instructions for minimum and maximum slopes; requirements can vary for driveways, accessible routes, and drainage systems.
Re‑measure after compaction or settlement. Freshly placed soil or gravel can shift, subtly changing the slope over the first season.
This tool only calculates geometric slope based on your measurements; it does not account for soil type, infiltration rate, rainfall intensity, or stormwater regulations.
It assumes a straight, uniform run. Complex sites with curves, dips, or multiple slope breaks may need to be broken into segments or modeled in more detail.
The calculator does not size pipes, inlets, or drainage channels; hydraulic design for stormwater systems requires additional calculations.
Accessibility and safety standards (such as ADA limits on ramp slopes) are not enforced here—always cross‑check against applicable codes.
Results are only as accurate as your measurements; using rough measurements or eyeballing slopes can produce misleading numbers.

Worked examples

Example 1: 6 inches of drop over 10 feet

Run = 10 ft, drop = 6 in.
Slope % = [6 ÷ (10 × 12)] × 100 = (6 ÷ 120) × 100 = 0.05 × 100 = 5%.
Inches per foot = 6 ÷ 10 = 0.6 in/ft.
Interpretation: this is a relatively steep slope compared to a typical 1–2% patio grade and is more like the aggressive fall often recommended immediately away from foundations.

Example 2: Patio with 1.5 inches of fall over 10 feet

Run = 10 ft, drop = 1.5 in.
Slope % = [1.5 ÷ (10 × 12)] × 100 = (1.5 ÷ 120) × 100 ≈ 0.0125 × 100 ≈ 1.25%.
Inches per foot = 1.5 ÷ 10 = 0.15 in/ft.
Interpretation: a 1.25% slope (around 1/8 inch per foot) is a common target for patios and walkways where you want water to drain but do not want a noticeable tilt underfoot.

Example 3: French drain trench dropping 8 inches over 40 feet

Run = 40 ft, drop = 8 in.
Slope % = [8 ÷ (40 × 12)] × 100 = (8 ÷ 480) × 100 ≈ 0.0167 × 100 ≈ 1.67%.
Inches per foot = 8 ÷ 40 = 0.2 in/ft.
Interpretation: a trench with about 0.2 inches of fall per foot typically gives enough grade for water to move consistently toward the outlet without creating a very deep trench at the low end.

Deep dive

Use this drainage slope calculator to turn simple field measurements into usable slope values in both percent and inches per foot. By entering the horizontal run and vertical drop of your driveway, patio, sidewalk, or yard grade, you can quickly see whether the surface will carry water away from structures instead of letting it pond.

Because the tool outputs both slope percentage and inches of drop per foot, it fits the way builders, inspectors, and DIYers actually talk about grade. That makes it easy to check your work against common guidelines like 1–2% slope for hardscapes or more aggressive fall away from foundations and trouble spots.

Pair this grade calculator with site‑specific guidance from local codes, building pros, or landscape designers to refine your plan. It is ideal for quick sanity checks during planning, layout, and inspection stages of small drainage and grading projects.

FAQs

What slope is recommended immediately away from a foundation?: A common rule of thumb is at least 6 inches of fall over the first 10 feet away from the foundation, which is roughly a 5% slope. Some codes or local practices may specify slightly different values, so always check regional guidance and consider soil conditions.
Is 1% slope enough for patios and sidewalks?: Many patios and sidewalks are built between about 1% and 2% slope (roughly 1/8–1/4 inch per foot). Around 1% can work if the surface is smooth and well‑drained; if you regularly see puddles, you may need a bit more slope or additional drainage features.
Does soil type or surface material affect the slope I should use?: Yes. Clay soils and tight surfaces shed water more quickly and may need more attention to drainage, while sandy or well‑draining soils can handle gentle slopes better. This calculator only reports geometric slope, so combine its output with knowledge of your soil, surface material, and climate.
How do I measure slope accurately on site?: A simple method is to use a string line and a small bubble level. Stretch the string from the high point to the low point, level the string, and measure the vertical distance from the string down to the surface at the low end. That drop, along with the horizontal distance between stakes, gives you the inputs for this calculator.
Can I use metric measurements with this drainage slope calculator?: The inputs are in feet and inches because those units match most North American building and landscape guidance. You can still use metric by converting meters to feet and centimeters to inches before entering values, then interpret the slope outputs (percent and inches per foot) against typical design recommendations.

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This drainage slope calculator provides grade estimates based on simple rise‑over‑run math and is intended for planning and educational use. It does not replace site‑specific engineering, stormwater design, or local building and drainage codes. Always verify critical drainage decisions with qualified professionals and consider erosion control, soil behavior, and regulatory requirements.