Gravel Sizes Explained: 3/4, G1, Crushed vs Natural, Base Course vs Concrete Aggregate

"Gravel" covers everything from pea-sized chips to fist-sized stone, sold under inch sizes, millimetre sizes, ASTM size numbers and yard codes that mean different things in different towns. This guide lines those names up, explains crushed versus natural gravel, and clears up the most expensive confusion of all: base course is not concrete aggregate.

Inches, millimetres and size numbers

Aggregate sizes are named after sieve openings. Inch names are older; specifications now use millimetres, and ASTM C33 adds size numbers that describe a whole grading, not a single sieve. The local names in the last column are trade usage only; no standard defines them.

Inch name	Sieve size	ASTM C33 size number	Local trade names (not standardised)
3/8"	9.5 mm	No. 8 (9.5 to 2.36 mm)	Chips, pea gravel, 3/8
1/2"	12.5 mm	No. 7 (12.5 to 4.75 mm)	1/2, chips
3/4"	19 mm	No. 67 (19 to 4.75 mm)	3/4, G1
1"	25 mm	No. 57 (25 to 4.75 mm)	1 inch
1-1/2"	37.5 mm	No. 467 (37.5 to 4.75 mm) or No. 4 (37.5 to 19 mm)	1-1/2, sometimes G2
"3/4 minus"	19 or 25 mm down to dust	Not a C33 concrete grading	Crusher run, base course, sub-base

The size name is the nominal maximum size: nearly everything passes that sieve, a small amount may be retained, and everything passes the next sieve up. A "3/4 gravel" that contains many 37.5 mm pieces is not 3/4 gravel, whatever the delivery receipt says. The C33 envelopes behind each size number are in the guide on aggregate gradation for DPWH specifications.

What "3/4" and "G1" mean in practice

Across much of the Philippine trade, "G1" is used for the 19 mm (3/4-inch) crushed gravel that goes into structural concrete. In some markets "G2" is the larger 37.5 mm stone; in others it is the smaller 3/8 chips, and a few yards number their products in their own order. None of these codes appear in ASTM C33 or in the DPWH Standard Specifications, so confirm what each source means by them.

The safe way to order is the millimetre size and the standard: "19 mm nominal crushed gravel, ASTM C33 Size No. 67". Add the local code in brackets if it helps the yard, and ask for the sieve analysis so the name and the material can be checked against each other.

Crushed gravel vs natural (river-run) gravel

Natural gravel is dug from rivers, terraces and pits and screened to size; the particles are rounded and smooth. Crushed gravel is produced by breaking rock or oversized river cobbles in a crusher; the particles are angular with fresh, rough faces. The general tendencies:

Property	Natural (rounded)	Crushed (angular)
Workability and pumpability	Generally better; particles roll past each other	Harsher; needs more paste or admixture
Water demand for the same slump	Generally lower	Generally higher
Bond with cement paste	Weaker (smooth surface)	Stronger (rough surface)
Interlock in base course	Poor; rounded stone rolls under compaction	Good; locks under the roller
Weak or weathered particles	The river sorts by size, not soundness, so check	Less likely when the parent rock is sound

For structural concrete either type can work if it meets the specification; many plants use crushed stone for strength and consistency, and natural gravel for pumpability where available. For base course, crushed material is preferred for its interlock, and DPWH specifies crushed aggregate base course as a separate item from aggregate base course; read the contract item for its fractured-face requirement. Asphalt specifications also commonly require fractured faces.

In Region XII both types are sold: screened and crushed river gravel, and crushed rock from quarries. Ask which one you are getting, because "3/4" alone does not say.

Base course vs concrete aggregate

This is the confusion that costs money. The two products can come from the same crusher and look similar in the truck, but they are graded for opposite purposes.

Concrete coarse aggregate is narrowly graded. A 19 mm gravel is almost all between 4.75 mm and 19 mm, with very little sand-size material and almost no dust: ASTM C33 limits material finer than 75 µm in coarse aggregate to 1.0%, or 1.5% for crushed aggregate where the fines are dust of fracture. The sand is added separately, in the proportion the mix design calls for.

Base course is densely graded. It runs continuously from the top size down through sand sizes to a controlled amount of fines, so it packs into a tight, stable layer under the roller. The DPWH items for aggregate subbase course, aggregate base course and crushed aggregate base course each define a grading envelope and limit the plasticity of the fines.

Swap them and both fail: clean 19 mm gravel used as base course rolls under traffic because nothing locks the stones together, and base course used as concrete aggregate brings unknown sand and clay-bearing fines into the mix, so strength drops and the mix design is meaningless.

"3/4 minus" or "crusher run" is a base-course-type product (19 mm down to dust), not a 3/4 concrete gravel. When a supplier says "base course", ask which pay item it is meant to satisfy and ask for the sieve analysis and plasticity result — and ask early, because whether a source holds current results for that product is a question to settle before the order, not after.

Which gravel for which job

Job	Gravel to ask for	Why
Footings, columns, beams, suspended slabs	19 mm (3/4), ASTM C33 No. 67	Passes between bars; the usual choice for reinforced concrete
Slabs on grade, pavements, mass concrete	25 mm (No. 57) or 37.5 mm (No. 467) where the specification allows	Lower paste demand; subject to the ACI 318 size rules and the DPWH item
Precast, hollow blocks, thin toppings	9.5 mm (No. 8) or 12.5 mm (No. 7)	Thin sections and smooth faces
Base course under pavements	Dense-graded to the DPWH aggregate base course or crushed aggregate base course item	Compaction and stability
Sub-base and general fill	DPWH aggregate subbase course item, or crusher run for non-DPWH work	Coarser envelope allowed
Driveways, yards, farm roads	Crusher run (3/4 or 1 inch minus)	Packs to a firm surface
French drains, drainage blankets, septic beds	Clean single-size 19–37.5 mm	Voids let water pass; no fines
Riprap and slope protection	Sized stone to the drawing and the DPWH riprap item	Mass and interlock against flow

Quality points beyond size

Size is the first check, not the only one. For concrete aggregate, look at:

• Los Angeles abrasion (ASTM C131): ASTM C33 allows up to 50% loss; DPWH concrete items set their own, tighter limit, so read the item in your contract.
• Soundness (ASTM C88): ASTM C33 limits the sodium sulfate loss of coarse aggregate to 12% (18% with magnesium sulfate).
• Fines: material finer than 75 µm at or below the C33 limit of 1.0 to 1.5%.
• Deleterious particles: clay lumps, soft particles, coal and chert within the ASTM C33 limits for the exposure class.
• Shape: some specifications limit flat and elongated particles, measured by ASTM D4791.

For base course, add plasticity of the fines, CBR and, for crushed aggregate base course, the fractured-face count. The guide on quality checks for batching-plant aggregates explains each test and what a certificate should show. Sand is a separate product with its own rules; see types of construction sand.

Illustrative scenarios

These are hypothetical situations, not project records.

• "G1" from a new yard turns out to be 37.5 mm stone that will not pass between beam bars at 25 mm spacing. The reorder is written as "19 mm nominal, ASTM C33 No. 67" and the problem does not recur.
• A subdivision road built on clean 3/4 gravel because it was in stock shoves under the first trucks and is replaced with dense-graded base course that compacts and holds.

How Stone Depot Trading helps

Stone Depot Trading coordinates B2B sourcing and supply of gravel, sand, limestone and fly ash through trade partner companies from General Santos City; it does not run a quarry or a laboratory. Send the size or gradation in millimetres, the standard or pay item, the quantity, the delivery location and the target date, and say which reports your specification requires — a sieve analysis, an abrasion result, a plasticity result. Availability, source, price and delivery terms are confirmed before quotation, and what the source can provide in the way of documents is asked of it and reported back rather than assumed (see limestone and gravel for road base).

FAQ

What size is 3/4 gravel in millimetres?

Nominally 19 mm: nearly all of it passes a 19 mm sieve and all of it passes 25 mm, with the sand-size fraction limited by the ASTM C33 Size No. 67 grading.

Is G1 the same as 3/4 gravel?

In much of the local trade, yes, G1 is used for the 19 mm crushed gravel that goes into concrete, but the code is not standardised and varies between yards. Confirm the size in millimetres and ask for the sieve analysis.

Can I use base course for concrete if I add cement?

No. Base course carries uncontrolled sand and clay-bearing fines; the resulting concrete is weaker and unpredictable. Use a graded concrete aggregate and a proper sand.

Is crushed gravel better than river gravel?

Crushed gravel gives better bond and better base-course interlock; rounded river gravel gives better workability and pumpability. Both can meet concrete specifications if the test results say so. For crushed aggregate base course, DPWH expects crushed material.

What is crusher run?

The unscreened product of a crusher below a stated top size, for example 19 or 25 mm down to dust. It is a base-course or surfacing material, not a concrete aggregate.

Request a quote

Send the size or gradation in millimetres, the standard or pay item, the quantity, the delivery location and the target date through the quote form, by email to cjandulana@stonedepotph.com, or by call or Viber to +63 945 643 5233. Submitting an inquiry starts a sourcing conversation; it does not create a binding order.

Sources

• ASTM C33/C33M, Standard Specification for Concrete Aggregates — ASTM International (https://store.astm.org/c0033_c0033m-18.html)
• ASTM C131/C131M, Standard Test Method for Resistance to Degradation of Small-Size Coarse Aggregate by Abrasion and Impact in the Los Angeles Machine — ASTM International (https://store.astm.org/c0131_c0131m-20.html)
• ASTM C88/C88M, Standard Test Method for Soundness of Aggregates by Use of Sodium Sulfate or Magnesium Sulfate — ASTM International (https://store.astm.org/c0088_c0088m-18.html)
• ASTM D4791, Standard Test Method for Flat Particles, Elongated Particles, or Flat and Elongated Particles in Coarse Aggregate — ASTM International (https://store.astm.org/d4791-19.html)
• DPWH Standard Specifications for Highways, Bridges and Airports, Volume II (2013 edition) — Department of Public Works and Highways
• ACI 318, Building Code Requirements for Structural Concrete — American Concrete Institute

Disclaimer

This article is general information. Final suitability of any material must be confirmed against the buyer's project specifications, the approved mix design, laboratory test results and the project engineer's requirements. Stone Depot Trading coordinates sourcing and supply; it does not certify materials or guarantee acceptance by any agency.