Soil Swell & Shrink Calculator
One cubic yard of soil is three different numbers. Convert between bank, loose and compacted volume using swell and shrink factors for your material.
The three states, and why they cost you money
Dig a cubic yard of clay out of the ground and you now have roughly 1.35 cubic yards sitting in a pile — the soil bulked up with air voids as it broke apart. That is swell, and it is what fills your trucks. Push that same clay back into a fill and roll it, and it ends up at about 0.75 of its original bank volume. That is shrinkage.
Both directions come off the same bank number, which is why you cannot chain them. Loose is bank × (1 + swell). Compacted is bank × (1 − shrink). Going the other way, divide instead of multiplying.
The mistake that imports forty loads of dirt
A site shows 600 yards of cut and 600 yards of fill, so it gets called balanced. But the fill number is compacted volume, and at 20% shrinkage those 600 compacted yards need 750 bank yards to build. The site is 150 bank yards short before a machine turns a wheel — and nobody finds out until the last lift will not come up to grade.
Take your cut and fill takeoff through this converter before calling a site balanced, then size the haul with the truck load calculator.
Rock does not shrink
Blasted rock is the exception worth remembering: it swells 50-60% coming out and never compacts back to where it started. Its shrink factor is negative, so a rock cut produces more compacted fill than the hole it came from — useful when you have somewhere to put it, expensive when you do not.
Frequently asked questions
What is the difference between bank, loose and compacted volume?
Bank is soil undisturbed in the ground — what your cut takeoff measures. Loose is the same soil after digging, when it has bulked up with air voids — what fills the truck. Compacted is after it is placed and rolled, when it takes up less room than it did in the bank. One cubic yard of material is three different numbers depending on which state you are quoting.
What is a typical swell factor?
Common ranges: sand and gravel 10-18%, loam around 25%, common earth 25%, clay 25-40%, blasted rock 50-60%. Swell is why a 100 cubic yard dig fills roughly 125 cubic yards of truck. Site conditions and moisture move these numbers, so treat the built-in defaults as a starting point and use your own values when you have them.
What is a typical shrink factor?
Shrinkage from bank to compacted usually runs 10-30%: sand and gravel around 12%, common earth 10-15%, clay 20-30%. Rock is the exception — blasted rock never returns to bank volume, so it shows negative shrinkage and takes up more room compacted than it did in the ground.
How many bank yards do I need for 500 compacted yards of fill?
Divide compacted volume by one minus the shrink factor. At 20% shrinkage, 500 compacted yards needs 500 ÷ 0.80 = 625 bank yards. Getting this backwards — multiplying instead of dividing — is the most common way a balanced site turns into an import job halfway through.