Fill Dirt & Excavation Calculator
Defaults to 20%, in the middle of the 15–30% range typical soil expands by once dug out. Adjust it for your specific soil type.
Enter the length, width and depth of a hole or trench, and adjust the swell factor if you know your soil type. This calculator returns the plain excavated (in-ground) volume alongside the swelled figure, the loose spoil volume that actually has to be hauled away or replaced.
Swell vs. Compaction: Two Different Numbers
Swell factor
Swelled Volume = Excavated Volume × Swell Factor
Typically 1.15–1.30 depending on soil type, this calculator defaults to 1.20 (20%).
"Excavated volume" and "swelled volume" answer different questions, and mixing them up is the most common sizing mistake in this kind of job. The excavated figure, plain length × width × depth, tells you how big the hole is. The swelled figure tells you how much material actually comes out of that hole once it's dug, which is always more, because loose soil traps more air between particles than compacted in-ground soil does. A 100 ft³ hole therefore produces noticeably more than 100 ft³ of spoil to cart away.
Going the other direction, backfilling, flips the logic again. Filling that same hole back in with compacted material actually needs more than 100 ft³ of imported fill once it's tamped down, because compaction is the reverse of swell: it squeezes the material tighter than its loose, as-delivered state. Size a disposal bin or haul-away truck against the swelled number, and size a backfill or import order against the compacted number, they're not the same figure even for the identical hole.
Where This Calculation Comes Up
Foundation and footing excavation for a concrete pour is the most common case, knowing the swelled spoil volume before digging tells you whether you need a disposal bin at all or whether the material can be spread on-site. Pool and pond excavation, utility trenching, and basement or crawlspace digouts all follow the same swell logic, just at larger scale. On the opposite end, if you're bringing in fill to raise a low spot in a yard rather than digging one out, the same calculator works in reverse, treat the target fill volume as the "compacted" figure and order accordingly.
Soil Type Changes the Swell Factor
| Soil Type | Typical Swell |
|---|---|
| Dense clay | 10–15% |
| Mixed native soil / loam | 15–25% |
| Sand or loose gravel | 20–30% |
| Rock (blasted or broken) | up to 50–60% |
Dense, cohesive soils like clay hold together in larger clumps when excavated, leaving fewer air gaps than loose sand or gravel does, which is why clay swells less even though it feels heavier and harder to dig. Broken rock is the extreme case: the excavated material bears almost no resemblance to its in-ground packing, since a solid mass has been shattered into loose fragments with substantial air space between them. If you know or can guess which category your site's soil falls into, adjust this calculator's swell factor to match rather than leaving it at the 20% default built for mixed, unspecified soil.
Worked Example: A Foundation Trench
A trench 30 ft long, 2 ft wide, 3 ft deep
- Excavated volume: 30 × 2 × 3 = 180 ft³
- Apply a 20% swell factor: 180 × 1.20 = 216 ft³
- Convert to cubic yards: 216 ÷ 27 = 8 yd³
Size the disposal bin or haul-away order for 8 cubic yards of loose spoil.
The bare 180 ft³ figure (6.67 yd³) is the number a structural drawing would show, always order against the swelled figure instead, or the truck comes back short.
Disposal, Reuse and Cost
Once spoil is calculated, the next decision is what happens to it, and that decision usually comes down to soil quality more than volume. Clean, unmixed native soil with no debris or contamination is often reusable elsewhere on the same site as backfill or fill for grading a low spot, which avoids both a disposal cost and a separate purchase of imported fill. Soil mixed with construction debris, old foundation material or any contamination has to be hauled to a licensed disposal or recycling facility instead, typically at a cost scaled to the swelled volume this calculator produces, not the smaller in-ground figure.
Because disposal is usually priced by volume or by the truckload rather than by weight, getting the swelled figure right before calling a hauler is where this calculator earns its keep financially, not just logistically, underestimating means an unplanned second load; overestimating means paying for a larger bin or truck than the job needed.
Timing an Excavation Job
Soil moisture at the time of digging affects both how easy the excavation is and how much the spoil actually swells. Saturated soil after heavy rain is heavier to move and can swell somewhat differently than the same soil dug dry, since waterlogged clumps break apart differently than dry, crumbly ones. Where possible, scheduling excavation after a dry spell rather than immediately following heavy rain makes the job physically easier and keeps the swell factor closer to the standard ranges this calculator is built around, rather than the more variable behavior of fully saturated ground.
Frozen ground is the opposite extreme worth planning around in cold climates, frozen soil doesn't excavate or swell like unfrozen soil at all, and machinery that handles unfrozen dirt easily can struggle significantly with a frozen surface layer. If a project's timeline spans a seasonal freeze, get the excavation figure calculated and the work scheduled before the ground freezes rather than after.
Coordinating Excavation With Utility Locates
Before any excavation deep enough to reach buried utility lines, typically anything beyond about 12–18 inches, though this varies by area, most jurisdictions require a utility locate request, commonly handled through a call-before-you-dig service, before work begins. This doesn't change the volume this calculator produces, but it does affect timing: locate requests often take several business days to process, so it's worth submitting one as soon as you have a calculated volume and a planned dig date, rather than waiting until material is already ordered and a crew is scheduled to show up.
Grading and Drainage After Backfilling
Once backfill material is in and compacted, the finished grade around the excavation should slope gently away from any structure rather than sitting flat or sloping toward it, a common cause of water intrusion problems traces back to backfill that settled flat or inward after the fact, undoing what looked like a correctly-graded surface right after the work was finished. Planning for that eventual settling by slightly overfilling and grading generously outward from the start, rather than grading to a perfectly flat finish, helps the site hold its intended slope even after the backfill continues to settle over the following months.
Frequently Asked Questions
Why does dirt take up more space once it's dug out of the ground?
Soil in the ground is compacted by the weight of everything above and around it; once excavated, it relaxes and the particles settle more loosely, trapping more air between them, a phenomenon called swell or bulking, typically adding 15–30% to the in-ground volume.
Should I size a disposal bin against the excavated or the swelled volume?
The swelled volume, a dumpster or hauling truck has to hold the loose, bulked-up spoil as it actually comes out of the ground, not the tighter volume the same dirt occupied while still in place. Sizing against the tighter figure instead risks needing a second bin once the swelled spoil does not fit.
Why does backfilling a hole need more than just the dirt that came out of it?
Because backfill has to be compacted as it goes back in to avoid future settling, and compaction takes up less space than loose fill, you typically need more imported material by volume than the excavated figure alone to fully compact a hole back to grade.
Does swell percentage vary much by soil type?
Yes, dense clay swells less than loose sandy or gravelly soil, which is why this calculator's swell factor is adjustable rather than fixed. When in doubt, 20% (the calculator's default) is a reasonable middle estimate for mixed native soil, while sandy or gravelly ground can swell closer to 30%.