Compaction Degree Calculator
Dry density and compaction degree from field density, with a pass/fail check.
Quick answer
With the default inputs: Field wet density 1.95 g/cm³ · Moisture content 12% · Max dry density 1.85 g/cm³ etc.Degree of compaction 94.1%
Edit the inputs below to recalculate.Inputs
Result
Degree of compaction
94.1%
| Dry density | 1.741g/cm³ |
| Max dry density | 1.850g/cm³ |
| Required | 94% |
| Verdict | Pass |
| Margin | 0.1% |
| Void ratio (Gs 2.70) | 0.551 |
| Dry mass per m³ | 1741kg/m³ |
| Dry density still required | 0.000g/cm³ |
Compaction is field dry density over laboratory maximum dry density. Wet density comes from the ring or sand replacement method, moisture by oven drying at 105-110°C to constant mass. Keep moisture within ±2% of optimum.
Reverse: known result, work out one input
Enter a target result; the other inputs stay fixed and this one is worked out.
Formula
| Dry density | ρd = wet density ÷ (1 + w) |
| Compaction | K = ρd ÷ ρd,max × 100% |
| Void ratio | e = Gs × ρw ÷ ρd − 1 |
| Verdict | Pass where K ≥ required |
Wet density 1.95 g/cm³ at 12% moisture with a 1.85 g/cm³ maximum: dry density 1.741 g/cm³ gives 94.1% compaction — a pass against 94%, but with only 0.1 point to spare.
Typical compaction requirements by location (design governs)
| Location | Required λc | Testing frequency |
|---|---|---|
| Ground slab subgrade | 0.90 | Every 100-200 m² |
| General backfill | 0.93 | Every layer, every 100 m² |
| Building footing backfill | 0.94 | Every layer, every 50 m² |
| Pipe trench backfill | 0.93 | Every layer, every 20 m |
| Retaining wall backfill | 0.94 | Every layer, every 50 m² |
| Road subgrade | 0.95 | Every 200 m per lane |
How to work it out
- Sample on site: use the ring cutter for fine-grained soil and the sand replacement method for coarse fill or rockfill.
- Measure wet density: with the ring cutter, ring volume and sample mass give it directly in g/cm³.
- Measure moisture content: oven dry a representative sample at 105-110 °C to constant mass and express the water as a percentage of dry soil mass.
- Compute dry density: ρd = ρ / (1 + w), with w as a decimal (12% is 0.12). This is the step that matters; comparing wet density directly is wrong.
- Degree of compaction = measured dry density ÷ maximum dry density × 100%, compared against the specification to pass or fail.
Where it goes wrong
- Comparing wet density with maximum dry density — wet density includes the water; at 12% moisture the dry density is 12% lower, which inflates the result by more than ten points and passes material that fails.
- Borrowing a maximum dry density from another source — it comes from a Proctor test on that specific soil from that borrow pit; using someone else's figure is not testing.
- Estimating moisture content by experience — more than 2% away from optimum and compaction simply will not reach the target.
- Sampling only the surface — backfill goes down in 300 mm layers and the sample belongs in the lower third of each layer; the surface is the best-compacted part.
Material and cost
Ring cutter test 50-150 CNY per point, sand replacement 100-200, Proctor test 800-2000 per set. Roller 300-800 CNY per shift, plate compactor 100-200.
On site
- Keep fill within 2% of optimum moisture. Too dry and it will not compact, too wet and it pumps; pumping soil must be removed and replaced.
- Layer thickness: 200-250 mm for plate compactors, 300-400 mm for rollers. Deeper than that and the bottom never gets compacted.
- Test frequency: at least one point per 100 m² for pits, one per 20-50 m for strip footings.
Basis
- GB/T 50123-2019 Standard for geotechnical testing methods
- GB 50202-2018 Code for acceptance of foundation construction, Chapter 9
- JTG 3430-2020 Field test methods of soils for highway engineering
FAQ
Why not compare wet density directly?
Water occupies volume without adding strength. Water the same soil and the wet density rises while compaction has not changed, so wet-density checks pass falsely in the rainy season. Convert to dry density — water volume removed — to measure how densely the particles themselves are packed.
What if compaction fails?
Separate moisture from effort. More than ±2% from optimum and rolling simply will not work — dry or wet the soil, then re-roll. If moisture is right and density is low, the passes or roller weight were insufficient; add passes. Never cover a failing layer with the next one.
Where does the maximum dry density come from?
A laboratory Proctor test (standard or modified) on the same soil as the fill. Values cannot be borrowed from another job or replaced by rules of thumb — the same soil from different sources can differ by over 0.1 g/cm³, which is 5 points of compaction. Re-test when the borrow area changes.
Cite this page
Use this format in reports, method statements or coursework. The link is permanent.
Building Calculator. Compaction Degree Calculator. 2026-10-25. https://jianzhujisuan.com/en/compaction
Results are estimating aids only and are not a design basis. Construction and final accounts must follow the drawings, the applicable standards and an approved method statement. Anything affecting structural safety, shoring or falsework must be checked by a suitably qualified engineer.