Road Base and Subbase Calculator
Calculate compacted volume and delivered tonnage of granular base or subbase, including the bulking allowance between loose and compacted material.
Formula
Compacted volume × compacted density gives the tonnage. The bulking factor converts compacted volume into the loose volume that will be delivered.
- Compacted volume (m³) = L × W × T
- Mass (kg) = Compacted volume × Compacted density × (1 + wastage % ÷ 100)
- Loose volume (m³) = Compacted volume × (1 + bulking % ÷ 100) × (1 + wastage % ÷ 100)
Worked example
A 100 m × 8 m road with a 200 mm compacted base at 2200 kg/m³, 25% bulking and 5% wastage.
- Area = 100 × 8 = 800 m²
- Compacted volume = 800 × 0.20 = 160 m³
- Mass = 160 × 2200 = 352,000 kg = 352 t
- With 5% wastage = 369.6 t
- Loose volume = 160 × 1.25 × 1.05 = 210 m³
Around 370 tonnes, arriving as roughly 210 m³ of loose material.
Assumptions and limitations
- Compacted density is the in-place dry density you expect to achieve, which follows from the laboratory maximum dry density and the specified degree of compaction. It is a project value, not a constant.
- The bulking factor is a delivery and haulage planning figure. It does not change the mass ordered — only the truck volume.
- Material is assumed uniform. Segregated or oversized material behaves differently and may not reach the assumed density.
- The calculation is for one layer. Multi-lift construction should be calculated per lift.
What this calculator does not do
- Does not design the pavement layer or specify compaction requirements.
- Does not check the layer against maximum lift thickness — see the guidance shown with the result.
- Does not account for moisture content at the weighbridge.
Practical tips
- Buy granular material by weight where you can. Volume-based ordering is where bulking disputes start, because the supplier measures loose and you measure compacted.
- Check the specified maximum lift thickness before you order. Placing a 300 mm layer in one pass when the specification allows 200 mm compacted will fail density testing.
- Moisture content matters at the weighbridge. Wet aggregate weighs more per cubic metre than the same material dry, and you pay for the water.
Frequently asked questions
How much road base do I need?
Multiply area by compacted thickness for the compacted volume, then multiply by the compacted dry density for tonnage. Add a wastage allowance, typically around 5%.
What is a bulking factor?
Loose aggregate occupies more space than the same material compacted. The bulking factor is the extra volume required — commonly 20–30% for crushed granular material. It tells you the delivered truck volume, not the weight.
Why does tonnage not change when I change the bulking factor?
Because bulking is about volume, not mass. The same tonnes of stone simply take up more room loose than compacted. Only the loose volume figure moves.
What density should I use for crushed aggregate base?
Take it from your compaction test results — the laboratory maximum dry density multiplied by the specified degree of compaction. Well-graded crushed material often lands around 2100–2300 kg/m³ in place, but the material and specification govern.
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Estimating tool, not a design. This calculator works out quantities from the dimensions you enter. It does not size any structural member, verify a design, or confirm compliance with any building code. Check every result against your project specification and applicable local standards, and involve a qualified engineer where the work requires one.