CalculatorAsphalt

Sub-base Calculator

Granular sub-base (GSB) tonnage for the layer between subgrade and base course.

Quick answer: Sub-base is the load-spreading layer over raw subgrade, typically 115 lb/ft³ compacted. 8 in is the common flexible-pavement spec; thicker over clay or frost-prone soils.

How to use this calculator

  1. Enter Length in ft.
  2. Enter Width in ft.
  3. Enter Depth in in.
  4. Enter Price per ton in $.
  5. Press Calculate. The highlighted row is your order quantity; the note beneath it translates the number into real-world terms.

Formula & constants

Sub-base is the load-spreading layer over raw subgrade, typically 115 lb/ft³ compacted. 8 in is the common flexible-pavement spec; thicker over clay or frost-prone soils. Every default in the fields above is editable — when your supplier’s spec sheet lists a different density, coverage rate or price, enter that number instead. The waste and compaction allowances follow common trade practice; see our methodology page for the derivation of each formula and the standards it references.

Worked example. With length = 10 ft, width = 10 ft, depth = 8 in, price per ton = 35 $, the calculator returns:
Volume2.47 cu yd
Material needed4.03 tons
Estimated cost$141

One ton covers ~25 sq ft at 8 in deep.

Where this fits in the project

Aggregate quantities feed the layers above them: after excavation, base material is placed in compacted lifts before asphalt or concrete goes down. Convert your tonnage to trips with the truckload calculator before scheduling delivery.

How this connects to your project

No quantity stands alone — each material in the chain depends on the ones around it. These are the planning steps that pair with the sub-base calculator:

Frequently asked questions

Base vs sub-base — what’s the difference?

Sub-base is coarser, cheaper material directly on subgrade; base course is tighter-graded stone directly under the pavement.

When can sub-base be skipped?

On strong granular subgrades (CBR > 8–10) light-duty pavements may use base course only — verify with local practice.

Last verified: — prices reflect current national averages. See our methodology.

Estimates are for planning. Material densities, coverage rates and prices vary by region and supplier — confirm final quantities before ordering, and check local code where structural or electrical work is involved.