Zerdly

Fill Bulking (Swell & Shrinkage) Calculator

Convert earthworks quantities between bank (in-situ), loose (excavated) and compacted (in-fill) states using swell and shrinkage factors. Enter any one of the three volumes and the calculator solves the other two, so you can move from a survey cut/fill volume to the loose volume you have to cart and the compacted volume you can actually place.

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How to use this calculator

Enter Values

Enter your values and press Calculate to see results.

Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.

How to use this calculator

  1. Enter ONE of the three volumes: bank (in-situ), loose (excavated) or compacted (in-fill), in cubic metres.
  2. Set the swell (bulking) factor — how much the soil expands when excavated (default 25%).
  3. Set the shrinkage factor — how much denser the material is after compaction than in-situ (default 10%).
  4. Read the other two volumes, plus the load factor (bank per loose m³) and shrinkage factor (compacted per bank m³).

How it works

The three states relate to the bank (in-situ) volume through two multipliers. Loose volume = bank × (1 + swell/100), because breaking undisturbed ground into a spoil heap introduces voids and bulks it up. Compacted volume = bank × (1 − shrink/100), because compacting placed fill squeezes it denser than the original ground. If you enter loose, the tool first back-solves bank = loose / (1 + swell/100); if you enter compacted, bank = compacted / (1 − shrink/100). The load factor = 1 / (1 + swell/100) is the bank cubic metres per loose cubic metre (used for haulage), and the shrinkage factor (1 − shrink/100) is the compacted cubic metres per bank cubic metre (used to balance cut and fill).

Worked example

Worked example. Excavate 100 m³ of bank (in-situ) soil at 25% swell and 10% shrinkage. Loose = 100 × 1.25 = 125 m³ to load and cart; compacted = 100 × 0.90 = 90 m³ placed in the fill. The load factor is 1 / 1.25 = 0.8, so every loose cubic metre in the truck represents 0.8 bank cubic metres.

Common mistakes

  • Confusing swell and shrinkage — swell bulks the loose (haul) volume UP, shrinkage brings the compacted (placed) volume DOWN relative to in-situ. They are different factors and act in opposite directions.
  • Applying a single generic factor to every material. Rock can swell 40–60% while sand may swell only 10–15%; always use site-specific values from a geotechnical report where the quantities matter.
  • Ordering imported fill by bank or loose volume when the design fill is a COMPACTED volume — you need more bank/loose material than the compacted volume you have to achieve.

Frequently asked questions

What is the difference between bank, loose and compacted volume?

Bank (or in-situ) is the volume of undisturbed ground before you dig. Loose is that same material after excavation, when it has swelled and bulked up in the truck or stockpile. Compacted is the volume it occupies once placed and compacted in a fill, which is denser (smaller) than the in-situ bank volume.

What swell and shrinkage factors should I use?

As a rough guide, swell is about 10–15% for sand and gravel, 20–30% for common earth and 40–60% for blasted rock; shrinkage is typically 5–15% for most soils. These vary a lot with material, moisture and compaction effort, so use values from a soil test or geotechnical report for anything more than a first estimate.

Why can compacted volume be less than the original ground volume?

Compaction removes air voids and rearranges particles more tightly than nature left them, so a given mass of soil occupies less space after compaction than it did in-situ. That reduction is the shrinkage factor, and it is why you must excavate (and often import) more bank material than the compacted fill volume you need to build.

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