Driveway cut and fill calculator

How this is calculated

Natural grade. Grade is rise over run expressed as a percentage: a driveway that climbs 10 ft over 200 ft is at 5 percent. The calculator takes the absolute value of the elevation change, so a driveway that drops to the house is treated the same as one that climbs.

When no earthwork is needed. If the natural grade is already at or below your target, the driveway can follow the ground. Cut and fill for grade are reported as zero. You still clear, shape a crown and ditches, and surface it, but you are not moving dirt to change the slope.

The wedge. If the ground is steeper than the target, the far end has to come down (or the near end come up) by the difference between the two grades multiplied by the length. On a straight run of uniform slope, the material between the natural ground line and the new design line is a triangle in profile: zero depth at one end, depth h at the other. Extruded across the driveway width, that triangle is a wedge whose volume is half of length times depth times width. Dividing by 27 converts cubic feet to cubic yards.

Cut versus fill. A balanced regrade pivots the design line about the middle of the run: the uphill half is cut, the downhill half is filled with that material, and the volumes are equal. The calculator reports that split. If your contractor instead cuts the whole wedge and hauls it off, or imports fill for all of it, the one-sided volume is the total earthwork figure, not the cut figure.

Length to reach target grade. Dividing the elevation change by the target grade gives the run that would carry the same rise at that grade with no cut or fill. If it is much longer than your straight-line distance, the answer is a longer alignment, a switchback, or accepting a steeper grade, not more dirt.

Cochise County defaults

• Target grade: 8 percent. The county's Road Design and Construction Standards (2017 edition) set a maximum of 7 percent on arterial and major collector roads and 10 percent on minor collector and local roads for runs not exceeding 600 ft, with a 0.25 percent minimum for drainage. The county does not set a maximum for the private portion of a driveway on your own parcel. For a gravel or compacted-caliche surface, about 10 percent is the practical ceiling before the surface washes and tires spin.
• Width: 14 to 16 ft. The county's residential driveway handout gives a preferred width of 16 ft and a range of 12 ft minimum to 30 ft maximum for the apron where it meets a county road. Count the vehicles that will come up it before the house is done: drill rig, septic tank truck, water hauler, lumber and concrete trucks.
• Permit. A right-of-way permit is required before you build the connection to a county road; the apron follows Standard Detail CC205-1 and needs a minimum 18-inch culvert where a drainage structure is required. Highway and Floodplain Department, 1415 Melody Lane, Building F, Bisbee; 520-432-9300; highway@cochise.az.gov. A driveway that stays on your parcel and out of the public right-of-way is on the county's list of single-family residential work that typically needs no building permit; floodplain and grading rules can still apply.
• Elevation data. For a first pass, USGS 3DEP lidar-derived elevation models (including the seamless 1-meter DEM where available) give the elevation at each end of the route. For the number you build to, use a level and grade rod or a drone photogrammetry survey of the actual route. Phone GPS altitude is not good enough.
• Soil. Much of the valley floor has cemented caliche within a few feet of the surface. A cut through it needs a ripper or breaker, and the time and cost per yard are not what the same volume of sandy loam costs. Broken caliche compacts into a usable running surface, which can offset the haul.

A worked example

A 300 ft driveway, 14 ft wide, climbing 40 ft from the road to a bench where the house pad goes, with an 8 percent target. Natural grade: 40 ÷ 300 × 100 = 13.3 percent, over target. Depth of the wedge at the far end: (13.3 − 8) ÷ 100 × 300 = 16 ft. Volume: ½ × 300 × 16 × 14 = 33,600 ft³, or 1,244.4 yd³ total, reported as 622.2 yd³ cut and 622.2 yd³ fill. Length to hit 8 percent without earthwork: 40 ÷ 8 × 100 = 500 ft. A 16-foot-deep cut at the top of a 300 ft drive is not something you want; the 500 ft alignment, or a switchback, is the real option.

The default inputs, 200 ft, 14 ft, 10 ft of rise, 8 percent target: natural grade 5 percent, within target, 0 yd³, and 125 ft would already carry that rise at 8 percent.

What this does not cover

• Real terrain. The wedge assumes a straight run on a uniform slope. A route that crosses a wash, a hump or a side-slope needs cross-sections every 25 to 50 ft, which is what a grading contractor or a drone survey produces.
• Cross-slope, crown and ditches. A rural driveway needs 2 to 5 percent cross-slope and drainage on the uphill side; that earthwork is not in the figure.
• Shrink and swell. Excavated material bulks when loosened and loses volume when compacted as fill. The calculator reports in-place volume; your contractor applies their own factors for haul and compaction.
• Surfacing. Aggregate base, chip seal or compacted caliche is a separate volume on top of the finished grade.
• Culverts, low-water crossings, erosion control and the apron at the county road.
• Cost. Per-yard rates depend on access, soil, rock and how far the contractor's machine travels to reach you. Get a bid against a plan.
• Curves and switchbacks. Enter the length along the path; the volume still assumes the grade is uniform along it.

Sources

• Cochise County — Residential Driveway Handout (PDF) — widths, radii, spacing, drainage, right-of-way permit, Highway and Floodplain Department contact.
• Cochise County — Engineering and Natural Resources — right-of-way and encroachment permits, driveway handouts.
• Cochise County Road Design and Construction Standards and Specifications for Public Improvements, 2017 edition (PDF) — maximum and minimum road grades, driveway section, Standard Details CC205-1 to CC205-4.
• Cochise County — Permit Exemptions — driveways outside a public right-of-way listed among residential work that typically needs no building permit.
• USGS 3D Elevation Program (3DEP) — lidar-based elevation data and digital elevation models.

Related guides

• Building a Rural Driveway in Cochise County: Permits, Base, Culverts
• Building Pad Specification Checklist for Cochise County Quotes
• Where to Buy ABC, Base Rock and Fill in Cochise County