Drainage & Slope Projects

Water problems are really slope problems: water stands where the ground fails to move it, and it moves wherever the grade tells it to go. This hub collects the calculators, specification guides, and cost references for diagnosing wet yards, setting grades, and building French drains that still work in ten years.

Work the problem in order: diagnose where the water comes from and where it can legally go, set or verify grades, then size the drain materials only if grading alone cannot solve it. The most expensive drainage mistake is burying a pipe with no outlet.

Calculators

CalculatorFrench Drain CalculatorComplete materials list: trench volume, washed stone in tons, pipe sections, filter fabric, and required elevation drop.Open calculator → CalculatorSlope & Grade CalculatorConvert rise/run, percent, and degrees; fall in inches over any distance for string-line setting.Open calculator → CalculatorExcavation & Trench CalculatorTrench spoil volume with swell, truckloads, and disposal planning for the dig.Open calculator →

Planning guides

DrainageWhat Is a French Drain?How the system works, when it is the right fix, and the anatomy of a correct build.Read guide → DrainageGravel for a French DrainStone size, washed versus fines, tonnage math, and why the wrong rock clogs the system.Read guide → DrainageWhat Slope Does a French Drain Need?The 1% standard, how to set it with a string line, and what happens when it is flatter.Read guide → DrainageWhy French Drains FailThe five failure modes, how to diagnose each, and what a rebuild costs versus doing it right.Read guide → DrainageFrench Drain vs. SwaleBuried pipe or shaped ground: which fix matches which water problem, with costs.Read guide → DrainageHow to Fix Standing Water in a YardThe four causes and the fix for each, from regrading to drains to downspout extensions.Read guide → SlopeHow to Calculate Percent GradeRise over run in the field with a string line and level, plus target grades by application.Read guide → SlopePercent Grade to DegreesThe conversion formula and chart, and why 100% is 45 degrees, not vertical.Read guide →

Costs & budgeting

CostsFrench Drain Cost (2026)Per-linear-foot pricing for yard, perimeter, and interior systems, plus a DIY materials budget.Read guide → CostsExcavation Cost Guide (2026)What the digging portion of a drainage project costs by the yard, hour, and trench foot.Read guide →

The one rule that governs every drain

Water needs somewhere lower to go. Before buying a foot of pipe, confirm the outlet: daylight on a downhill slope, a storm drain where permitted, or a dry well, and verify it sits lower than the entire pipe run at your chosen slope. The French drain calculator computes the total elevation drop your run requires, and the slope calculator converts it to a string-line measurement. Formulas and standards are documented in our methodology.

Frequently Asked Questions

How much does a French drain cost in 2026?

Exterior yard drains run $10 to $65 per linear foot installed depending on depth, with deep perimeter drains at $30 to $90. Interior basement systems cost $40 to $100 per linear foot, or $4,000 to $17,000 for a full perimeter.

What slope does drainage need?

Drain pipe needs a minimum 1% slope (1/8 inch per foot). Patios and walkways should shed water at 2%, and the ground next to a foundation should fall 5% (6 inches over the first 10 feet) away from the house.

Why do French drains fail?

Almost always clogging: no filter fabric, the wrong stone (fines or rounded pea gravel), or no positive outlet. A properly built drain with washed angular stone, a fabric-lined trench, and a real outlet lasts decades.

Do I fix grading or install a drain first?

Grading first. Surface water problems are usually cheaper to fix by reshaping the ground than by burying pipe, and many standing-water problems disappear with correct grade alone. Drains handle the water grading cannot.