Gravel & Sub-Base Calculator
Work out the gravel sub-base under a slab or driveway in cubic yards and tons, with a compaction allowance so you order enough.
Calculator
300 sq ft of sub-base at 4" is about 4.07 yd³ (5.7 tons) including 10% compaction.
A slab is only as good as the base under it, and gravel sub-base is sold two ways — by the cubic yard and by the ton. This calculator gives you both from the area and depth, and adds a compaction allowance because loose gravel loses volume once it is tamped down. Order to the compacted figure so you are not short a few inches at the far corner.
Formula
yd³ = area × (depth_in ÷ 12) ÷ 27 × (1 + compaction%)
tons = yd³ × 1.4 (labeled compacted-gravel density)
Worked example
300 sq ft at a 4 in base with 10% compaction:
- Loose = 300 × (4 ÷ 12) ÷ 27 = 3.70 yd³
- With compaction = 3.70 × 1.10 = 4.07 yd³
- Tons = 4.07 × 1.4 = 5.7 tons
Depth, compaction & density
Sub-base depth for residential flatwork is commonly 4–6 in of compacted crushed stone, deeper for driveways or poor soils — a labeled planning typical, not a soils spec. The 1.4 tons per cubic yard density is a labeled figure for compacted crushed aggregate; your quarry’s exact number varies with stone type and moisture, so confirm it when you order by weight. Compaction matters: gravel dumped loose settles 10–20% under a plate compactor, and if you order to the loose volume you will run out. This is the same math as our gravel base for a driveway tool.