Introduction
Not all dirt behaves like dirt. Clay swells when wet and shrinks when dry; sand drains freely but won’t hold a slope; rock barely changes volume at all but costs a fortune to move. The cut and fill math is identical for every site – but the shrink factors, swell percentages, and compaction behavior that feed the math change completely with soil type. Using generic factors on the wrong material is how estimates go wrong while looking right.
The Cut and Fill Calculator computes your cut, fill, and net balance in cubic yards and cubic meters from the dimensions you enter. This guide tells you what those numbers mean for the actual material on your site – how each soil type swells, shrinks, compacts, and performs as fill.
The Materials You’ll Encounter
Topsoil
The dark, organic surface layer, typically 15-30 cm (6-12 in) deep. High organic content makes it compressible and unstable – it is never structural fill. Strip it, stockpile it separately, and respread it for final landscaping. Its volume is computed separately and kept out of the cut/fill balance.
Common earth / loam
Mixed soil of sand, silt, and clay – the default material on most residential sites. Digs easily, compacts well at proper moisture, and behaves predictably. All the “typical” factors used in estimating (swell 25-30%, shrink factor 0.85-0.90) describe this material.
Clay
Cohesive, sticky when wet, rock-hard when dry. Clay compacts to a dense, strong fill but is extremely moisture-sensitive: too wet and it pumps under rollers, too dry and it won’t densify. It also swells and shrinks with moisture changes after placement, which can heave slabs and pavements. Clay cut is usable as fill only with careful moisture control and thin lifts.
Sand and gravel
Granular, free-draining, and the best structural fill available. Compacts easily – often with vibration rather than heavy rolling – and doesn’t change volume with moisture. The tradeoff: it won’t hold a steep slope without support, and clean sand can be difficult to excavate cleanly in deep cuts without shoring. If your cut is granular, treat it as premium fill and protect it from contamination.
Rock
Bedrock, large boulders, or heavily cemented material. Swell and shrink are minimal (rock doesn’t compact back down), but excavation cost can be several times common-earth rates and may require ripping or breaking equipment. Rock cut is generally unsuitable as structural fill unless crushed and graded – plan on exporting it and importing engineered fill for structural zones.
Swell and Shrink by Material
| Material | Typical swell (bank to loose) | Typical shrink factor (bank to compacted) | Fill suitability |
|---|---|---|---|
| Common earth / loam | 25-30% | 0.85-0.90 | Good |
| Clay | 30-40% | 0.80-0.90 | Fair – moisture-critical |
| Sand | 10-15% | 0.90-0.95 | Excellent |
| Gravel | 10-15% | 0.90-0.95 | Excellent |
| Rock (broken) | 40-60% | 0.70-0.80 | Poor unless crushed/graded |
| Topsoil | 30-40% | 0.75-0.85 | Non-structural only |
These are typical ranges for planning, not constants – actual values vary with gradation, moisture, and compaction effort. The table’s message is directional: granular soils are efficient (little volume lost), clay is moisture-fussy, and rock is a different business entirely. How these factors enter the net balance formula is derived in the formula-explained guide.
How Material Changes the Worked Example
Take the standard 50 ft x 40 ft pad: 111.1 bank yd3 of cut, 74.1 compacted yd3 of fill. Watch what the shrink factor does to the true surplus:
- Sand cut (shrink 0.93): 111.1 x 0.93 = 103.3 yd3 fill available; surplus = 29.2 yd3.
- Common earth (shrink 0.90): 111.1 x 0.90 = 100.0 yd3; surplus = 25.9 yd3.
- Clay cut (shrink 0.85): 111.1 x 0.85 = 94.4 yd3; surplus = 20.3 yd3.
Same site, same measurements – the export quantity swings from 20 to 29 yd3 on material alone. And for hauling, clay’s higher swell (say 35%) turns that 20.3 yd3 surplus into about 27 loose yd3, while sand’s 12% swell turns 29.2 yd3 into about 33 loose yd3. Material assumptions move both ends of the job: what you can reuse and what the trucks carry.
Compaction Behavior
| Material | Best compaction method | Lift thickness | Key risk |
|---|---|---|---|
| Common earth | Sheepsfoot or smooth roller | 20-30 cm (8-12 in) | Moisture variation across the site |
| Clay | Sheepsfoot roller, thin lifts | 15-20 cm (6-8 in) | Wet clay pumping; dry clay not densifying |
| Sand / gravel | Vibratory roller or plate | 20-30 cm (8-12 in) | Over-wetting causing instability |
The handful moisture test applies to every material: squeeze a sample – it should hold together and break cleanly. For structural pads (under foundations, slabs, or pavements), specify compaction testing through a geotechnical lab rather than judging by appearance. The field techniques are covered in the pro tips guide.
Matching Material to the Job
- Structural fill (under buildings, slabs, driveways): clean granular material – sand, gravel, or good common earth, properly compacted in lifts and verified by testing.
- General landscape fill: common earth or clay, compacted reasonably; minor settlement acceptable.
- Drainage features (swales, French drain surrounds): granular material only – clay in a drainage feature defeats its purpose.
- Topsoil zone (final 15-30 cm / 6-12 in): reserved for respread topsoil, never structural fill.
When your cut doesn’t match your fill needs – rocky cut on a site needing structural fill, for example – the honest answer is export plus import, not forcing unsuitable material into service. The economics of that tradeoff are worked through in the cost guide.
Related Guides
- Cut and Fill Calculator: Complete Guide – terminology, formulas, and the full worked example.
- Cut and Fill Calculator: Formula Explained – how shrink and swell enter the math.
- Cut and Fill Calculator Estimating Guide – field measurement workflow.
- Cut and Fill Calculator Cost Guide – how material affects hauling and import costs.
- Cut and Fill Calculator FAQ – quick answers to the most asked questions.
Frequently Asked Questions
Can I use clay as structural fill?
Yes, with conditions: place it in thin lifts at controlled moisture and compact properly. Clay is strong when correctly compacted but unforgiving of moisture errors, and it can swell and shrink with seasonal moisture changes. For critical structures, get geotechnical guidance.
Why does sand have a higher shrink factor than clay?
Granular particles pack efficiently with little volume change, so sand loses only 5-10% going from bank to compacted. Clay’s plate-like particles trap more air and water, so more volume is lost in compaction.
What do I do with rocky cut?
Broken rock swells 40-60% and compacts poorly, making it bad structural fill and expensive to haul. Typical practice: export it (or use it for non-structural landscaping) and import engineered fill for structural zones.
How do I identify my soil type?
Simple field checks: squeeze a moist handful (gritty and falls apart = sand; smooth and holds shape = clay; in between = loam), and dig a test hole to check layering and topsoil depth. For structural work or uncertain soils, a geotechnical investigation is the reliable answer.
Does topsoil count in my cut and fill?
No. Strip it, compute its volume separately, stockpile it, and respread it at the end. Including it in the structural balance distorts both cut and fill and contaminates the fill.
Get Your Number
Soil type doesn’t change the formulas – it changes the factors inside them, and the factors change the answer. Identify your material, use its shrink and swell ranges instead of generic ones, and match each soil to a suitable use. Then run your measurements through the Cut and Fill Calculator with material-appropriate assumptions, and the volumes you price will reflect the ground you actually have.
Disclaimer: Calculator results are planning estimates based on the dimensions you enter. Swell and shrink values are typical ranges that vary with specific soil conditions, moisture, and compaction effort. Verify quantities with your contractor and consult a geotechnical professional or your local building authority for structural fill decisions.
