Enter weights, volumes, and moisture to compute unit weight. Choose metric or imperial units. View moist, dry, saturated, and buoyant results with exports fast.
| Case | Volume (m³) | Total Weight (kN) | Moisture (%) | Bulk Unit Weight (kN/m³) | Estimated Dry Unit Weight (kN/m³) |
|---|---|---|---|---|---|
| Compaction test specimen | 0.0100 | 0.2000 | 12 | 20.0000 | 17.8571 |
| Borrow soil sample | 0.0125 | 0.2100 | 18 | 16.8000 | 14.2373 |
| Backfill quality check | 0.0080 | 0.1500 | 10 | 18.7500 | 17.0455 |
Unit weight links soil mass to volume, driving earth pressures and surcharge loads. Designers use it for lateral pressure diagrams, footing checks, and haul planning. Field teams use it to verify borrow suitability and compaction. Small measurement errors in volume can shift calculated unit weight noticeably for cut and fill.
Most compacted sands fall near 16 to 20 kN/m³, while silts often range 14 to 19 kN/m³. Lean clays commonly sit 15 to 19 kN/m³. Below groundwater, saturated values can reach 19 to 22 kN/m³. In imperial terms, 100 to 140 pcf covers many fills projects.
Bulk unit weight uses moist weight and reflects current water content. Dry unit weight removes water mass and is the basis for compaction control, Proctor comparisons, and percent compaction reporting. If moisture is available, the calculator estimates dry weight using Wd = Wt divided by (1 + w) in routine quality control.
When void ratio and specific gravity are known, saturated unit weight can be estimated for soils below the water table. Submerged unit weight equals saturated unit weight minus water unit weight, representing buoyant reduction. This value is used with effective stress concepts for seepage, stability, and uplift checks in practice.
Use consistent units and measure volume carefully with molds, sand cone, or water displacement methods. Weigh samples promptly to limit evaporation. Record moisture content from oven drying and avoid mixing disturbed and undisturbed volumes. For cohesive soils, trim specimens cleanly to reduce trapped voids and scale errors note ambient temperature.
Compare computed dry unit weight with specification targets and laboratory maximum dry density. A low dry unit weight may indicate inadequate compaction, excessive lift thickness, or poor moisture conditioning. High bulk unit weight can reflect wetting or overcompaction. Use trends across locations, not single points, to decide for site control.
Volume errors dominate when samples are small. Moisture gradients, organic content, and gravel oversize can distort representative density. If the sample loses fines during handling, the calculated unit weight increases artificially. In frozen or very wet soils, note that meltwater or drainage changes weight during testing. Use larger samples carefully.
Log the location, depth, test method, and equipment calibration. Report both bulk and dry unit weight when moisture varies. For groundwater influence, include saturated and submerged values with assumptions for Gs, void ratio, and water unit weight. Export CSV for daily summaries and PDF for submittals and audit trails records.
Use the bulk unit weight for short term conditions matching current moisture. If groundwater is present or anticipated, check saturated and submerged values as well. When unsure, use conservative ranges from your geotechnical report and confirm with field density tests.
Yes, if you have volume, total weight, and moisture content, you can estimate dry unit weight using Wd = Wt/(1+w). A Proctor test is still needed to compare against maximum dry density and determine percent compaction targets.
High values often come from underestimating volume, losing fines, or weighing after partial drainage. Recheck specimen trimming, container tare, and moisture sampling. For clays, ensure the volume represents the intact sample and avoid squeezing water during handling.
Use laboratory results when available. For many mineral soils, Gs commonly ranges 2.60–2.75. Void ratio varies widely with gradation and compaction; site specific tests are best. If estimating, document assumptions and run sensitivity checks on saturated results.
In saturated soil, submerged unit weight equals saturated unit weight minus water unit weight. It represents the buoyant unit weight used to compute effective stresses below the water table. Effective unit weight is often used as a practical synonym in geotechnical calculations.
No. It helps compute unit weights from measured inputs and supports quick checks. Field testing methods like sand cone, nuclear gauge, or balloon density provide the data needed for acceptance. Use this tool to standardize calculations and reporting.
Match the units in your drawings and specifications. Metric outputs are in kN/m³, while imperial outputs are in pcf. Keep weight and volume consistent within the same system, and only convert final results if required for reporting.
Soil unit weight is a core input for earth pressure, bearing capacity, slope stability, and temporary works. Bulk unit weight reflects in-situ moisture, while dry unit weight is used for compaction control and material comparison. Saturated unit weight matters below the water table, and submerged unit weight governs effective stresses in saturated conditions.
Use accurate unit weights to build safer foundations always.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.