Swale Calculator
A swale moves water by grading a shallow channel, and getting the dirt volume right tells you whether you’re hauling material off-site or bringing it in. Enter your swale’s length, width, and cut/fill depths to get cubic yards and haul cost.
Swell = bulking when dug (bank → loose). Shrink = reduction once compacted (loose → compacted).
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Hauling notes
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Details
Swale volume starts with area: multiply the swale’s length by its width to get square footage. Multiply that by the cut depth (material removed) and separately by the fill depth (material added), each converted from inches to feet, then divide by 27 to get cubic yards for each. Subtract fill from cut to see whether you have net material to haul away (export) or need to bring material in (import), then divide by truck capacity to estimate loads and hauling cost.
Swale Sizing Guidelines
Swale dimensions depend on how much water the channel needs to carry and how much room you have to work with.
| Situation | Typical Width | Typical Depth |
|---|---|---|
| Minor yard drainage | 2-4 ft | 4-6 in |
| Standard drainage swale | 4-6 ft | 6-10 in |
| Higher-volume runoff (large lot, steep grade) | 6-10 ft | 10-18 in |
| Bioswale with plantings | 4-8 ft | 6-12 in, with engineered soil mix |
How to calculate swale cut and fill volume
- Measure the swale’s length and width in feet.
- Set the cut depth how deep you’re excavating the channel, in inches.
- Set the fill depth how much material you’re adding back, if any, in inches.
- Calculate cut and fill volume separately, then subtract to find the net cubic yards to move.
- Estimate hauling divide net volume by your truck’s capacity to get loads and haul cost.
Worked example
Here’s the math for an 80 ft long, 4 ft wide swale with an 8 in cut depth and no fill.
- Swale area320 sq ft (80 ft x 4 ft)
- Cut depth8 in
- Fill depth0 in
- Cut volume9.9 cu yd
- Fill volume0.0 cu yd
- Net volume9.9 cu yd (export)
- Truck loads1 load
- Haul cost$177.78
Grading a swale that actually drains
A swale only works if water keeps moving toward its outlet, so slope matters more than exact width or depth. Aim for a minimum grade of 1-2% (about 1/8 to 1/4 in of drop per foot of length) along the full run, with no flat or back-pitched sections where water can pool and sit. On a longer swale, check the grade with a laser level or string line every 10-20 ft rather than eyeballing it end to end, since a flat spot in the middle can undo an otherwise good slope. Route the outlet somewhere the water is actually allowed to go, like a storm drain, dry well, or a spot well away from your own or a neighbor’s foundation, and check local drainage rules before directing runoff onto adjacent property.
Common mistakes
- Building a swale with no consistent slopeA flat or uneven-grade swale collects standing water instead of moving it, which defeats the purpose and can attract mosquitoes.
- Underestimating truck loads on export jobsExcavated soil expands (swells) compared to its in-ground volume, so a truck rated for a certain cubic yardage of compacted fill carries less loose, swelled material per load.
- Ignoring the outlet pointA well-graded swale that dumps water against a foundation, a neighbor’s yard, or a spot with nowhere to go just relocates the drainage problem.
- Skipping erosion controlBare soil in a new swale erodes fast during the first few rains. Sod, seed, or riprap at the outlet keeps the channel intact.
What this calculator assumes
Adjust your result if your project differs from these.
- Swale is measured as a simple rectangular channel (length by width), not a complex compound-slope shape.
- Cut and fill depths are treated as uniform across the swale’s full length and width.
- Truck capacity and haul cost are based on the values entered for your hauler or rental truck.
- Net volume determines direction, export if cut exceeds fill, import if fill exceeds cut.
Common questions
What slope does a drainage swale need?
A minimum of 1-2% grade, roughly 1/8 to 1/4 in of drop per foot, is standard so water keeps moving instead of pooling.
Where does excavated swale soil go?
If you don’t need it elsewhere on the property for fill, it’s typically hauled off-site, which is what this calculator’s haul cost estimates.
Can I use a swale on a mostly flat lot?
A swale needs some grade to function. On a very flat lot, you may need to import fill on one end to create enough slope, which this calculator can also estimate.
Do I need a permit to build a swale?
Rules vary by city and county, especially where the swale crosses a property line or discharges toward a neighbor’s lot. Check local drainage regulations before digging.
How is truck load count calculated?
Net cubic yards to move is divided by your entered truck capacity, then rounded up to a full load since a truck can’t make a partial trip.
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Swale Calculator Result
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materialcalculate.com/tools/swale-calculator/
Result
| Area | — |
| Cut volume | — |
| Fill volume | — |
| Net | — |
| Truck loads | — |
| Estimated haul cost | — |
Notes
Estimate generated by materialcalculate.com.