Flexible base gravel and crushed stone
Flex Base Calculator
Answer first: a 4-inch flex base layer for a 20×20 ft area needs about 2.5 tons of crushed limestone. Flex base (flexible base) is a compacted crushed stone sub-base used under concrete slabs, driveways, and roads in Texas and southern US. This calculator gives you tons, cubic yards, and delivery cost so you can order accurately.
20×20 ft driveway pad at 4 inches depth
~2.5 tons of flex base
Standard 4-in compacted depth for a residential driveway. Flex base compacts about 20%, so you need 25% more loose material than the finished depth.
50×20 ft driveway at 6 inches depth
~9.3 tons of flex base
6-in depth is standard for heavy truck traffic or areas with weak subgrade. At $20-30/ton delivered, that is $186-$279 for the base material alone.
Material cost reference
$20–$35 per ton delivered (Texas average)
Flex base prices vary by region and distance from quarry. Northern states may call it "road base" or "crushed limestone base" at similar prices.
Compaction factor
20–25% shrinkage after compaction
Always order 20-25% more than your calculated volume to account for compaction. A 4-in loose layer compacts to about 3.2 inches after rolling.
Interactive workflow
Run the numbers, then save or export the project
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How many tons of flex base do I need for a driveway?
Formula: Length (ft) × Width (ft) × Depth (in) ÷ 12 ÷ 27 × 1.4 (tons/yd³) × 1.2 (compaction). Example: a 20×20 ft driveway at 4 in compacted = 400 × 0.333 ÷ 27 × 1.4 × 1.2 = 2.5 tons. A 300 ft × 12 ft driveway at 6 in = about 84 cubic yards = 118 tons. Always order 20–25% more than your compacted volume to account for compaction shrinkage.
What is the difference between flex base and road base?
Flex base and road base are regional names for the same type of crushed aggregate sub-base material. Flex base is the Texas term (TxDOT Item 247). Road base is used in most other states. Crusher run is common in the Southeast. All three are blended gradations of crushed stone that compact tightly for driveways and roads. The material itself is essentially identical — the name just tells you where you are.
How deep should flex base be for a driveway?
Standard residential driveways: 4 inches compacted depth. Heavy vehicle traffic or areas with clay soil: 6 inches. TikTok and Reddit contractors confirm: "4-inch depth is really needed to keep everything from sinking even after scraping the wet stuff out" on clay soil. Compact in 4-inch lifts — do not place more than 4 inches without compacting between lifts. Use 6 inches for driveways with concrete on top.
How much does flex base cost per ton in 2026?
Flex base prices vary significantly by region. Texas (near quarries): $13–$22/ton delivered. Midwest: $18–$28/ton. Northeast/West Coast: $21–$35/ton. Trucking adds $5–$15/ton depending on distance. Reddit farmers report: same 20-truck job cost $4,800 in Texas vs $14,000+ in Northeast USA. Always get 3 local quotes — quarry proximity is the biggest price driver.
What is the compaction factor for flex base?
Flex base and road base typically compact 20–25% from loose to finished depth. This means you must order 20–25% more loose material than your target compacted volume. A 5-inch loose layer becomes about 4 inches after compaction with a plate compactor or roller. The calculator automatically adds the 20% compaction factor — you just enter your finished depth.
What is a truck load of flex base (how many tons per truck)?
A standard dump truck carries 10–14 tons of flex base. A tandem axle truck carries 12–16 tons. A triaxle truck carries 18–22 tons. When calculating truck loads: divide your total tons by the truck capacity. For a 300 ft driveway needing 118 tons: 118 ÷ 14 = 8–9 truck loads. Minimum delivery charges may apply for small orders under 5–8 tons.
How do I compact flex base properly?
Compact flex base in 4-inch lifts using a plate compactor (for small areas) or a roller compactor (for driveways and roads). Lightly moisten the material before compacting — slightly damp material compacts better than bone-dry material. Make multiple passes until the material no longer shows visible movement. TikTok contractors show that skipping compaction leads to ruts and washboarding within months.
Can I use flex base under concrete?
Yes — flex base is an excellent sub-base under concrete slabs. Use 4–6 inches of compacted flex base under residential concrete driveways, patios, and slabs. The flex base provides drainage, prevents soil movement, and gives the concrete uniform bearing. In cold climates with freeze-thaw cycles, 6 inches of compacted base is recommended under all concrete to prevent frost heave.
How is flex base different from gravel for a driveway?
Flex base (crushed limestone with fines) compacts tightly and bonds together — it creates a solid, stable surface. Regular round gravel does not compact as well and shifts under tires. Pea gravel and crushed stone without fines drain well but do not lock together. For driveways, flex base or road base is superior to loose gravel because it creates a stable surface that holds vehicle weight without rutting.
What is TxDOT Type A flex base?
TxDOT Item 247 Type A flex base is the Texas Department of Transportation specification for flexible base material. It requires crushed limestone or caliche meeting specific gradation requirements — a blend of coarse aggregate and fines that compact tightly. Type A is the most common spec for Texas residential and commercial driveways. Type B uses different materials. For most residential projects, any crushed limestone meeting similar gradation is acceptable.
How many cubic yards are in a ton of flex base?
Flex base and crushed limestone weigh approximately 1.4 tons per cubic yard (or 2,800 lb/yd³). To convert: tons ÷ 1.4 = cubic yards. To convert cubic yards to tons: cubic yards × 1.4. Example: 10 tons of flex base = 10 ÷ 1.4 = 7.1 cubic yards. Heavier materials like granite weigh more (1.5–1.6 tons/yd³); lighter materials like caliche weigh less (1.2–1.3 tons/yd³).
What is crusher run and is it the same as flex base?
Crusher run is the Southeast US term for the same type of crushed aggregate sub-base. It is a blend of crushed stone with fines (dust) that compacts tightly. Regional names for the same material: flex base (Texas), road base (most states), crusher run (Southeast), processed gravel (Midwest), type 2 aggregate (some states). All work well for driveways and sub-bases. Use whatever your local quarry sells.
Planning disclaimer
Flex base calculations include a 20% compaction factor. Actual requirements vary by material gradation, compaction equipment, subgrade conditions, and depth. Always verify material specifications with your supplier and engineer.