Yard Slope & Grading Calculator
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Excavation & Grading
Grading & Slope Calculator
Quick answer: slope (%) = rise ÷ run × 100, with both in the same units. Ground that drops 6 in (0.5 ft) over 10 ft has a 5% slope — 0.6 in per foot, a 1:20 ratio, about 2.9°. That is exactly the minimum fall the IRC requires within 10 ft of a house foundation.
Three grading tools in one: convert a measured rise and run into percent, ratio, degrees, and inches per foot; find how much drop a target slope needs over a distance; and estimate cut or fill cubic yards and tons to bring an area to finished grade.
Rise, run, and string line
How to calculate grading slope and fill
Grading is about two numbers: how steeply the finished ground falls, and how much soil it takes to get there. Slope can be written four ways that all describe the same angle, so builders, landscapers, and code books often quote it differently.
Slope % = rise ÷ run × 100 · Drop = run × slope %
Fill yd³ = area (ft²) × average depth (ft) ÷ 27 × (1 + compaction %)
- Inches per foot = slope % × 0.12. A 2% slope is 0.24 in/ft; 1/4 in/ft is 2.08%.
- Ratio 1:x = run ÷ rise. 5% is 1:20; a 3:1 bank (3 ft out per 1 ft up) is 33%.
- Degrees = arctan(rise ÷ run). At yard slopes, degrees are small: 5% is only 2.9°.
- Drop for a target slope = distance × slope ÷ 100. Convert feet to inches by × 12.
- Cut or fill = area × average depth change ÷ 27. Add a compaction allowance to fill, or a swell allowance to soil you haul away.
Measuring with a string line and line level
Drive a stake at the high point (usually against the foundation) and another at the far end. Tie a mason's line to both, hang a line level at its center, and slide the knot until the bubble centers. Measure from the line down to the ground at each stake: the difference between the two readings is the rise, and the horizontal stake-to-stake distance is the run. For cut/fill, measure down to the ground every 5–10 ft in a grid and average the readings — that average is the "existing ground" input. Do the same with the finished heights you want to get the "finished grade" input.
Worked example: regrading a 30 × 40 ft backyard
Six string-line readings across the yard are 14, 11, 9, 12, 8, and 6 in, averaging 10 in below the line. The plan sets finished grade at an average of 5 in below the line, falling 6 in over the first 10 ft from the house (5%) and 2% beyond that.
- Average fill: 10 − 5 = 5 in (0.417 ft) over 1,200 ft²
- Compacted volume: 1,200 × 0.417 = 500 ft³ ÷ 27 = 18.52 yd³
- Order with 20% compaction allowance: 18.52 × 1.20 = 22.22 yd³, about 26.7 tons at 1.2 tons/yd³
- Fall: 6 in in the first 10 ft, then 30 ft × 2% = 7.2 in more to the back of the yard
Typical grading slopes for drainage
Common design ranges. Your local code, HOA, or engineer may require different values.
| Surface | Typical slope | Inches per foot | Drop per 10 ft |
|---|---|---|---|
| Soil within 10 ft of foundation (IRC R401.3) | 5% minimum (6 in in 10 ft) | 0.60 | 6.0 in |
| Paving within 10 ft of foundation (IRC R401.3) | 2% minimum | 0.24 | 2.4 in |
| Lawn areas away from the house | 1–2% minimum; 2% drains more reliably | 0.12–0.24 | 1.2–2.4 in |
| Patio (concrete or pavers) | 1–2% (about 1/8–1/4 in/ft) | 0.12–0.24 | 1.2–2.4 in |
| Driveway cross slope or crown | 1–2% or more | 0.12–0.24+ | 1.2–2.4+ in |
| Grass swale, along its length | 1–2% minimum | 0.12–0.24 | 1.2–2.4 in |
| Steepest bank most mowers handle (3:1) | 33% | 4.0 | 40 in |
Slope conversion chart
| Percent | Inches per foot | Ratio (1:x) | Degrees | Drop per 100 ft |
|---|---|---|---|---|
| 0.5% | 0.06 | 1:200 | 0.29° | 6 in |
| 1% | 0.12 | 1:100 | 0.57° | 12 in |
| 1.04% | 1/8 (0.125) | 1:96 | 0.60° | 12.5 in |
| 2% | 0.24 | 1:50 | 1.15° | 24 in |
| 2.08% | 1/4 (0.25) | 1:48 | 1.19° | 25 in |
| 5% | 0.60 | 1:20 | 2.86° | 60 in |
| 10% | 1.20 | 1:10 | 5.71° | 120 in |
| 25% | 3.00 | 1:4 | 14.04° | 300 in |
Grading tips and common mistakes
- Grade for where the water goes, not just away from the wall. Every slope needs a destination — a swale, street, dry well, or rain garden. Sending runoff onto a neighbor's lot can violate local ordinances.
- Keep soil below siding and weep screeds. Building codes and siding makers require clearance between finished grade and wood framing or siding (often 6 in or more). Raising the yard against the house to get slope can bury that gap.
- Use the right soil in the right place. Compactable fill or clay-rich soil near the foundation sheds water; finish with 4–6 in of topsoil where grass will grow. Sand or gravel next to the house lets water soak straight down.
- Compact in lifts. Place fill in layers of roughly 4–6 in and tamp or roll each one. A thick loose pile settles unevenly and creates low spots that hold water.
- Check slope after rain. Puddles that last more than a day mark low spots. Re-shoot those areas with the string line and add topsoil to restore the fall.
- Call 811 first. Even shallow grading with a skid steer can hit irrigation, gas, or electric lines.
Grading and slope FAQ
How do you calculate the slope of a yard?
Divide the rise (height change) by the run (horizontal distance) using the same units, then multiply by 100 for percent. A yard that drops 6 inches over 10 feet is 0.5 ÷ 10 = 0.05, or a 5 percent slope, which is also 0.6 inches per foot, a 1:20 ratio, or about 2.9 degrees.
How much should the ground slope away from a house?
The International Residential Code (section R401.3) requires the grade to fall at least 6 inches within the first 10 feet from the foundation, which is a 5 percent slope. Where lot lines or other barriers prevent that, drains or swales must carry water away instead, and impervious surfaces within 10 feet of the foundation must slope at least 2 percent away from the building.
What is a 2 percent slope in inches per foot?
A 2 percent slope is 0.24 inches of drop per foot, just under 1/4 inch per foot. Over 10 feet it falls 2.4 inches, and over 50 feet it falls 12 inches. A slope of exactly 1/4 inch per foot is 2.08 percent.
How do I calculate fill dirt for grading a yard?
Find the average fill depth across the area, multiply it in feet by the area in square feet, and divide by 27 for cubic yards. Then add 15 to 25 percent because loose soil compacts. Raising 1,200 square feet by an average of 5 inches takes 18.5 cubic yards compacted, or about 22.2 cubic yards delivered with a 20 percent allowance.
What is the minimum slope for a patio?
Patios are usually pitched 1 to 2 percent away from the house, which is about 1/8 to 1/4 inch per foot. A 12 foot deep patio at 2 percent drops about 2.9 inches from the house side to the outer edge.
How we built this calculator: results use the standard volume, area, and coverage formulas shown on this page, with typical U.S. material densities, bag yields, and waste factors that you can override. Written and checked by the YardsCalculator editorial team. Last reviewed: October 2026.