Fill Dirt Calculator
Yards of fill dirt for grading, leveling, or retaining
What is fill dirt calculator?
A fill dirt calculator answers the contractor’s first question on any grading or backfill project: how many cubic yards of structural fill do I need delivered. The volume math is straightforward — area times depth — but compaction allowance is significant, and the difference between fill dirt and topsoil is operationally important.
The default density is 95 lb/ft³, which is typical for moderately moist clay-and-rock fill. Wet clay-heavy fill runs 110-115 lb/ft³ and weighs 15-20% more per yard; the volume calculation doesn’t change, only the tonnage readout. Both densities assume properly compacted fill — loose-dumped is significantly lighter and shouldn’t be used for any structural quote.
What depth to use? There is no single standard — the right depth is whatever fill it takes to reach final grade or backfill the void. For foundation backfill, the depth equals the trench depth, and you must compact in 6-inch lifts to avoid voids near the wall. For yard regrades and slope work, use the average fill depth across the slope. For retaining wall backfill, structural fill behind the wall is essential and must be compacted in lifts.
Bulk vs bagged: fill dirt is bulk-only on any real job. Bagged products labeled “fill dirt” exist at home centers but cost many times more per yard than bulk. For anything past a wheelbarrow load, call an excavation or trucking supplier for a half-truck or full-truck delivery. Typical dump trucks haul 10-20 cubic yards.
The 10% waste factor default covers spread loss and minor over-fill. For structural fill that compacts in lifts — foundation backfill, retaining wall fill, anything load-bearing — bump to 25%. Fill dirt loses roughly 20-25% of its loose volume under proper mechanical compaction (plate compactor or jumping jack tamper). Order on the high side; leftover fill is easy to spread elsewhere on the site, but a return delivery costs another half day.
Always specify clean fill (no organic debris, rocks under 6 inches) for structural applications. Unscreened fill is cheaper and works fine for non-structural grading, but never for foundations or retaining walls — organic material decays and creates voids that compromise the structure years later.
When to use a fill dirt calculator
- Foundation backfill — Filling around a poured wall after the forms come off. Trench depth equals wall height; backfill compacts in 6-inch lifts.
- Slope regrade — Re-shape a sloped yard for drainage or a flat play area. Use average fill depth across the slope for the volume.
- Retaining wall fill — Behind a new retaining wall, structural fill is critical. Compact in lifts and order extra for the compaction allowance.
How to use the Fill Dirt Calculator
- Measure the area — For foundation trenches and retaining wall zones, multiply length by width by depth. For yard regrades, multiply area by average fill depth across the slope.
- Pick a depth — There's no standard depth for fill dirt — use whatever it takes to reach final grade. Compact in 6-inch lifts for structural applications (foundations, walls); 12-inch lifts are tolerable for non-structural grading.
- Read the volume — Bulk fill dirt is sold by the cubic yard at most excavation suppliers. Output shows yards directly; the tonnage figure is for trucking weight load reference (typical truck holds 10-20 yards).
- Apply waste factor — 10% covers spread loss and minor over-fill. Bump to 25% for structural fill that compacts in lifts — fill dirt loses roughly 20-25% of its loose volume under proper compaction.
Worked examples
Foundation backfill, 4 ft x 50 ft trench
Input: 4 ft x 50 ft x 8 ft depth
Output: 59.3 cu yd / 76.0 tons (with 10% waste)Yard regrade, 30 ft x 50 ft
Input: 30 ft x 50 ft x 6 in average
Output: 27.8 cu yd / 35.7 tonsUse average fill depth across the slope; the math is forgiving for grading work.
Retaining wall fill, 4 ft x 30 ft x 4 ft
Input: 4 ft x 30 ft x 4 ft depth
Output: 17.8 cu yd / 22.8 tons