Berm Volume Calculator
A berm looks simple until you try to order soil for one. The cross-section is a trapezoid, not a triangle, and the difference between the two shapes is the top width nobody measures. Guess a triangle and you under-order by a third; guess a rectangle and you over-order by half. Either way, the delivery truck is wrong on the day the crew shows up.
The Berm Volume Calculator below takes the trapezoid seriously: length, base width, top width, and height, with results in cubic feet, cubic yards, and truckloads. It also applies a compaction allowance, because loose soil settles and the volume you order is not the volume that stays.
Quick Answer
Key takeaways
- A berm’s cross-section is a trapezoid: area = (base + top) ÷ 2 × height. Triangles under-order by a third.
- Divide cubic feet by 27 for cubic yards, the unit suppliers use.
- Add 15-25% for compaction and settling, or you will run short after the soil settles.
- Measure height vertically from the lowest point, not along the slope face.
The trapezoid that most calculators skip
A berm’s cross-section is almost never a triangle. Real berms have a flat or rounded crest, which makes the shape a trapezoid: two parallel sides (the base width at the ground and the top width at the crest) separated by the height. The area is the average of the two parallel sides times the distance between them, and the volume is that area times the berm’s length. The Math Central berm analysis states it exactly this way: the cross-section area is the average of the parallel sides times the distance between them, multiplied by the length for volume.
The triangle shortcut is the expensive mistake. A 15 ft base with a 4 ft top and 4 ft height has a trapezoid area of 38 sq ft; the triangle version (base × height ÷ 2) gives 30 sq ft, under-ordering by more than 20%. And the compaction allowance is the second most skipped step: loose soil settles, so fill-dirt guides recommend ordering 15-25% extra depending on soil type, 10-15% for screened fill, up to 25% for clay-heavy soils.
Worked example, checked against this exact tool
Enter the pre-filled defaults (100 ft long, 15 ft base, 4 ft top, 4 ft height, 15% compaction) and click Calculate:
| Figure | Value |
|---|---|
| Cross-section area | 38 sq ft ((15 + 4) ÷ 2 × 4) |
| Geometric volume | 3,800 ft³ (38 × 100), or 140.7 cy |
| Compaction allowance | +15% (21.1 cy) |
| Soil to order | 161.9 cubic yards |
| Truckloads | 12 (at 14 cy per load) |
Try the sharp-ridge case with top width 0: the area becomes (15 + 0) ÷ 2 × 4 = 30 sq ft and the order drops to about 127.8 cy. Same footprint, nearly 21% less soil, which is exactly why the top width matters.
Measuring a berm without guessing
Four measurements, all in feet. Length is the long run of the berm. Base width is the footprint at the ground. Top width is the crest; for a rounded crest, measure where the slope clearly flattens. Height is vertical, from the lowest adjacent ground to the crest, measured with a level and a stick or a laser level, never along the slope face. For irregular berms, break the run into segments, compute each, and add them.
Two practical notes. First, a 3:1 slope (three feet horizontal per foot of height) is the common rule for stable, mowable berms; steeper slopes erode. Second, topsoil and fill dirt are different products: use fill dirt for the berm’s structure and reserve topsoil for the top few inches where plants grow. If the berm is part of a larger yard project, an irrigation system cost calculator can help budget the watering side of the new landscaping.
What competing berm calculators miss
We checked the top-ranking berm and fill calculators. Three gaps keep showing up.
No top width. Most tools ask for length, width, and height and compute a triangle or a box. The top width is the measurement that makes a berm a berm, and skipping it is the main source of under-ordering.
No compaction allowance. Several calculators give the geometric volume and stop. Ordering exactly the geometric volume guarantees a shortfall after settling. The allowance selector here is matched to soil-type guidance.
No truckload figure. Cubic yards are what suppliers quote, but truckloads are what you schedule. The per-load row turns the abstract number into a delivery plan.
Frequently asked questions
Use the trapezoid formula: volume = length × (base width + top width) ÷ 2 × height, all in feet, then divide by 27 for cubic yards. Add 15-25% for compaction. A 100 ft berm with a 15 ft base, 4 ft top, and 4 ft height needs about 161.9 cubic yards ordered.
Compute the geometric volume in cubic feet, divide by 27, then add a compaction allowance. The calculator above does all three steps and converts to truckloads: a 140.7 cy berm with 15% compaction needs about 161.9 cy, or 12 loads at 14 cy each.
A 3:1 slope (3 feet of horizontal run per foot of height) is the standard for stable, mowable berms. Steeper slopes erode and are hard to maintain. With a 4 ft height and 3:1 slopes on both sides, the base naturally works out to about 24 ft plus the top width.
Fill dirt for the structure: it compacts well and supports the shape. Topsoil is for the top few inches where plants grow; it is less stable and not suitable for the load-bearing core. Screened fill dirt needs about 10-15% extra for compaction; clay-heavy soils need up to 25%.
Vertically, from the lowest adjacent ground to the target crest level, not along the slope face. Use a level and a measuring stick for small berms or a laser level for long runs. For irregular shapes, break the berm into segments and measure each.
About 7 loads at 14 cubic yards per truck (100 ÷ 14 = 7.1, rounded up). Check your hauler’s actual capacity: end dumps commonly carry 18-22 yards, which changes the count.
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References
- Math Central (University of Regina), “The volume of a berm” – trapezoid cross-section area as the average of the parallel sides times the distance between them, times length for volume. Math Central: The Volume of a Berm. Accessed October 19, 2026.
- HelloGravel, “How to Calculate Fill Dirt for a Slope” – triangular wedge formula, 15-25% compaction allowance by soil type, and vertical height measurement guidance. HelloGravel: Fill Dirt for a Slope. Accessed October 19, 2026.
- The Tech Edvocate, “How to calculate cy” – cubic yard conversions for prisms, cylinders, and triangular prisms, including berm shapes. The Tech Edvocate: How to Calculate Cubic Yards. Accessed October 19, 2026.