The sand cone test measures in-place density the slow, direct way: dig a hole, weigh the soil that came out, and find the volume of the hole by filling it with sand of known density. It needs no radioactive source and no license, which is why many labs keep the apparatus even when they run a nuclear gauge every day. It is also unforgiving: every number depends on the sand calibration and on careful weighing. This guide covers ASTM D1556 in plain terms and works through the arithmetic one line at a time.
What is a sand cone test?
Like the nuclear gauge, the sand cone test gives a dry density that is compared with a Proctor maximum dry density to get percent compaction. Labs use it where a gauge is not available or not allowed, to spot-check gauge results, and on materials where a direct measurement is preferred.
The method works best in soils that hold the shape of a hole without caving or deforming while you dig and fill it.
What equipment does the sand cone test need?
A sand cone apparatus (a jar with a valve and a funnel-shaped cone), a base plate, clean, dry, uniform calibration sand, a balance, digging tools, a sealed container for the excavated soil, and moisture determination equipment.
Two calibrations matter. The bulk density of the sand, in pcf, tells you how much volume a given mass of sand occupies. The mass of sand needed to fill the cone and base plate tells you how much of the sand that leaves the jar never reaches the hole. Calibrate both for the sand you actually use, and recalibrate when you change sand.
How is a sand cone test performed?
Prepare a level surface and seat the base plate. Dig a hole through the plate opening, collecting every bit of excavated soil in a sealed container so no moisture escapes. Weigh the jar with its sand. Invert the apparatus on the plate, open the valve, and let sand fill the hole and cone until it stops flowing. Close the valve and weigh the jar again. Weigh the wet soil and determine its moisture content.
Avoid vibration near the apparatus while the sand is running. Vibration settles the sand more densely than during calibration and makes the hole look smaller than it is.
How do you calculate sand cone density?
Sand in hole = (initial mass of apparatus and sand − final mass) − sand needed to fill the cone. The subtraction of the cone mass is the step people forget, and it is a large share of the sand used.
Hole volume = sand in hole ÷ bulk density of sand. Wet density = wet soil mass ÷ hole volume. Dry density = wet density ÷ (1 + w/100). If you have the MDD, percent compaction = dry density ÷ MDD × 100.
Notice how the sand density flows through every result. A sand density that is off by a small percentage moves the hole volume, the wet density and the dry density by the same percentage. That is why calibration is not paperwork; it is the measurement.
How should a sand cone result be judged?
Once you have a dry density, compare it with the right Proctor. As with any field density test, the reference must be the same material and the method the specification calls for. A sand cone result compared with the wrong MDD is just as misleading as a nuclear result compared with the wrong one.
Look at the hole itself before you trust the number. A hole with a large stone on one side, a cavity that collapsed partway through filling, or a wall that bulged while the sand ran are all reasons to note the condition or move to a new location. The arithmetic will happily produce a precise-looking density from a bad hole.
Keep the raw readings on the field sheet: both jar masses, the cone value, the sand density and the calibration it came from, the wet soil mass and the moisture determination. With those, anyone can rerun the chain of four formulas and get the same answer, which is the real test of a good record.
What formulas are used?
- 01Sand in hole = (initial − final) − sand to fill the cone
- 02Hole volume = sand in hole ÷ sand bulk density
- 03Wet density = wet soil mass ÷ hole volume
- 04Dry density = wet density ÷ (1 + w/100)
What does a worked example look like?
Inputs
Sand bulk density 100.0 pcf. Apparatus and sand: initial 15.00 lb, final 8.50 lb. Sand needed to fill the cone 1.20 lb. Wet soil from the hole 6.50 lb. Moisture 9.0 %.
Result
Sand that left the jar: 6.50 lb. Sand in hole 5.30 lb. Hole volume 0.0530 ft³. Wet density 122.6 pcf. Dry density 112.5 pcf. Had the cone mass been left out, the hole would have looked larger and the density noticeably lower, which shows how much that one subtraction matters.
Calculated by the same tested functions as the ProofGrit free calculators.
How do you turn a sand cone result into percent compaction?
Divide the dry density by the Proctor MDD for the same material and multiply by 100. Report percent compaction to 0.1 % and decide pass or fail on that displayed value. The moisture content used for dry density should come from a sample of the soil taken out of the hole.
When a sand cone is used to check a nuclear gauge reading at the same spot, expect some difference, since the methods measure differently and over different volumes. A large difference is worth investigating rather than averaging away.
What are the most common sand cone mistakes?
Forgetting to subtract the cone, which makes the hole look much larger and the density much lower.
Using a sand density from a different batch of sand.
Losing excavated soil or letting it dry before weighing.
Digging a hole with loose material left on the walls or bottom.
Running equipment nearby while sand is flowing.
Rounding intermediate values. Keep full precision through the chain and round only the reported densities.
Which standards relate to ASTM D1556?
ASTM D698 and ASTM D1557 supply the MDD. ASTM D2216 covers oven-dry moisture content of the soil removed from the hole. ASTM D6938 is the nuclear alternative. See the standards index for the full list.
See the standards index for every standard covered on this site.
| Item | Sand cone (D1556) | Nuclear gauge (D6938) |
|---|---|---|
| Volume found by | Calibrated sand filling the hole | Gauge measurement |
| Moisture from | Removed soil, oven-dried | Gauge reading |
| Field time | Longer | Shorter |
| Radiation licensing | Not needed | Required |
Frequently asked questions
How often should the sand be calibrated?
Follow the current standard and your lab procedure, and always recalibrate when you change to a new batch or source of sand.
Why do I need the cone mass?
Some of the sand that leaves the jar fills the cone and plate opening, not the hole. The calibrated cone mass removes it from the calculation.
Can I use any dry sand?
Use clean, dry, uniform sand suited to the method, and calibrate it. Its bulk density sets the hole volume.
Does the test give percent compaction?
Yes, once you divide the dry density by the Proctor MDD for the same material and multiply by 100.
Why might sand cone and nuclear results differ?
They measure in different ways and over slightly different volumes. Investigate large differences rather than averaging them away.
How ProofGrit helps
The free ProofGrit sand cone calculator takes the sand density, cone mass, before and after jar masses, wet soil mass and moisture, and shows each intermediate value: sand in hole, hole volume, wet and dry density, and percent compaction when you enter the MDD. It catches impossible inputs, such as a final mass that leaves no sand in the hole. It runs in your browser and saves nothing.
Related guides and tools
- Nuclear density test: field compaction with ASTM D6938How the nuclear gauge test works, the dry density and percent compaction math, the daily standard count check, and the mistakes that cause retests.
- The Proctor test: how it works and how to read the curveWhat a Proctor test measures, how each compaction point is calculated, how the curve gives MDD and OMC, and how the zero air voids line keeps you honest.
- Standard vs Modified Proctor: ASTM D698 and D1557 comparedHow Standard (D698) and Modified (D1557) Proctor differ in rammer, drop and layers, why Modified gives a higher MDD, and why the right reference matters.
- Soil compaction testing: field and lab guideHow laboratory Proctor references, field density tests and project acceptance work together in soil compaction testing.
- Sand cone calculatorSand in the hole, hole volume, wet and dry density and percent compaction for the sand cone test.
- Soil moisture content calculatorWater mass, dry soil mass and moisture content from container, wet and dry weighings.
- Proctor curve calculatorWet and dry density per point, a fitted moisture-density curve with zero air voids line, MDD and OMC.
- Standards indexEvery ASTM, AASHTO and ACI standard explained on this site.
- All soil testing guidesBrowse the full guide library by topic.
Sources and further reading
- ASTM D1556/D1556M, density of soil in place by the sand-cone methodASTM International
- ASTM D2216, laboratory water (moisture) content of soil and rock by massASTM International
- ASTM D698, laboratory compaction using standard effortASTM International
- ASTM D1557, laboratory compaction using modified effortASTM International
Standards are summarized in our own words. Read the current edition from the publisher before you test.
This guide is a plain-English summary. Always follow the current standard and your project specifications.