Road Base Calculator
Find how much road base to order for a driveway, parking pad, or the base under pavers or asphalt. Enter each area's size and its thickness after compaction, and see the loose volume to order, the weight, and the bags. For loose gravel that is not compacted, use the Gravel Calculator.
Add more areas, or subtract areas that need no base, such as a planter.
- Choose US or Metric. This also sets the units of the results and the bag sizes: 0.5 cu ft bags for US, and 1 tonne, 850 kg, and 800 kg bulk bags and 22.5 kg bags for Metric.
- Pick the shape of the area and enter its dimensions. For a shape that is not listed, choose Known area and enter the area directly.
- Enter the Compacted thickness: the thickness of the base after it is compacted, as in your plans or a paving guide, not the loose depth you spread.
- Use Add section for each extra area. Set a section to Subtract for parts that need no base, such as a planter.
- Check the Density and the Compaction factor. They start at 137 lb/ft³ after compaction and 1.3. If your supplier gives other values, enter them. The reset links under the fields bring back the defaults.
- Keep the 10% waste allowance or change it. If your bag is not listed, enter the volume or weight printed on the bag in Custom bag size.
- Optionally, enter a price per US ton, tonne, cubic yard, cubic foot, cubic meter, or bag to estimate the cost.
The dimension and thickness fields accept whole numbers, decimals,
fractions, and mixed numbers, such as 12, 10.5,
3/4, or 2 1/2. The compaction factor accepts
whole numbers and decimals, such as 1.3 or
1.25.
How much road base you need
Road base is spread loose and compacted with a plate compactor or roller, which shrinks its volume. The calculator starts from the volume after compaction:
Compacted volume = area × compacted thickness × (1 + waste % ÷ 100)
Convert every dimension to the same unit before you multiply. With dimensions in feet, divide cubic feet by 27 to get cubic yards. The volume you order by the yard or meter is the loose volume, as it is measured in the truck or the bag:
Loose volume to order = compacted volume × compaction factor
Compacting doesn't change the weight, so the weight comes from the compacted volume and the density after compaction:
Weight = compacted volume × compacted density
If you buy by the ton or tonne, you don't need the compaction factor: the weight is the same with any factor. The factor only changes the loose volume, the bags labeled by volume, and the cost per cubic yard, cubic foot, or cubic meter.
Compaction factor and density
The compaction factor is the loose volume you need for each unit of compacted volume. The Washington State Department of Transportation (WSDOT) Design Manual lists the weight of crushed surfacing, its graded crushed base, both per cubic yard measured in the truck and per cubic yard compacted on the roadway. The ratio of the two is 1.25 for base course and 1.29 for top course. The calculator rounds this up to 1.3, so it doesn't order less than those ratios.
The factor depends on the grading and how hard the base is compacted. A 2023 Wisconsin DOT research report measured 1.34 to 1.52 for dense-graded base, but it measured the loose state in a box, looser than a load in a truck. If your supplier gives a factor, or a loose and a compacted weight per yard, enter the factor.
The default density is 137 lb/ft³ (1.85 US tons/yd³, or 2.195 t/m³), the compacted weight WSDOT lists for both grades of crushed surfacing. That is a dry weight. Base delivered damp weighs a few percent more, which the 10% waste allowance covers. At the default factor, the loose weight is about 1.42 US tons per cubic yard.
The waste allowance starts at 10%. The same WSDOT table says to add 10% when the material is stockpiled, as it usually is when a load is dumped on a driveway and spread from there.
Crusher run, MOT Type 1, and other names
Road base is crushed stone graded from coarse pieces down to fines, so it packs into a firm layer. It goes by many names: crusher run or crush and run, dense-graded aggregate base (DGA), class 2 base in California, base course, and MOT Type 1 sub-base in the UK. They are the same kind of material, so the calculator uses the same density and factor for all of them.
The density and factor are for crushed stone base. They don't fit sand or soil compacted as fill. Recycled concrete and asphalt millings compact differently, so ask your supplier for their density and factor and enter them.
How thick to make the base
The thickness depends on the traffic, the soil, and the climate, so the calculator leaves it blank. As a reference, the Concrete Masonry & Hardscapes Association (CMHA) calls for a compacted base at least 4 in (100 mm) thick under sidewalks, patios, and walkways, and at least 6 in (150 mm) under residential driveways, on well-drained soil. Wet or weak soil and cold climates need a thicker base. Follow your plans or a local guide.
Bags of road base
Bags are counted the way they are labeled. Bags labeled by volume hold loose base, so they are counted from the loose volume. Bags labeled by weight are counted from the weight. The calculator shows these bag sizes:
| Bag | Examples |
|---|---|
| 0.5 ft³ | Quikrete HardScapes Paver Base (US) |
| 1 tonne bulk | Howarth Timber, MOT Type 1 (UK) |
| 850 kg bulk | Kingfisher Direct, MOT Type 1 sub-base (UK) |
| 800 kg bulk | Wickes, MOT Type 1 Jumbo Bag (UK) |
| 22.5 kg | Wickes, MOT Type 1 Major Bag (UK) |
Wickes notes that bag weights may vary by about 5% with moisture, so the bag count is an estimate.
Examples
A patio base in feet
A 10 ft × 10 ft area with a 4 in compacted base is 33.33 ft³. With the 10% waste allowance, the compacted volume is 36.67 ft³ (1.36 yd³). Order 1.77 yd³ of loose base (36.67 × 1.3 = 47.67 ft³), which weighs 2.51 US tons (5,025 lb). In 0.5 cu ft bags, that is 96 bags (47.67 ÷ 0.5 = 95.33, rounded up). At $40 per US ton, the cost is $100.49. At $50 per cubic yard, it's $88.27.
Metric dimensions
A 5 m × 4 m area with a 150 mm compacted base is 3 m³. With 10% added, the compacted volume is 3.30 m³, and the loose volume to order is 4.29 m³. It weighs 7.24 tonnes (7,244 kg): 8 bulk bags of 1 tonne, 9 of 850 kg, 10 of 800 kg, or 322 bags of 22.5 kg. At £45 per tonne, the cost is £325.98.
FAQ
About 1.85 US tons (3,700 lb) per cubic yard after compaction, at the default density. A cubic yard of loose base, as delivered, is about 1.42 US tons at the default factor of 1.3. A cubic meter compacted weighs about 2.2 tonnes.
About 44 ft² at 4 in compacted, or 29 ft² at 6 in, before any waste allowance. A US ton is about 14.6 ft³ after compaction. A tonne covers about 4.6 m² at 100 mm, or 3 m² at 150 mm.
No. Compacting doesn't change the weight, so the tons come from the compacted volume and density alone. You need the factor only to order by the cubic yard or meter, or in bags labeled by volume.
Yes. Crusher run, crush and run, dense-graded aggregate base, and MOT Type 1 in the UK are all graded crushed stone that compacts into a base, and the calculator treats them the same. Check your supplier's density if it gives one.
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