Calculation Methodology
Every formula, unit factor, default value and rounding rule used by the calculators on this site, matched to the code that runs them. In short: area = length × width, volume = area × depth, an allowance you choose is added to the volume once, and volume × density = weight. Orders are rounded up to whole tons or tonnes; costs use the exact quantity. All calculations run in your browser.
Units and conversions
The calculators work internally in metres, cubic metres and kilograms, and convert to and from the units you choose with exact factors. The factors follow the definitions in NIST Special Publication 811 and NIST Handbook 44, Appendix C. A US ton is the short ton of 2,000 pounds; a tonne is 1,000 kilograms.
| Unit | Exact value in SI units | Used for |
|---|---|---|
| 1 inch | 0.0254 m | Depth |
| 1 foot | 0.3048 m | Length and width |
| 1 yard | 0.9144 m | Length |
| 1 cubic foot | 0.028316846592 m³ | Volume (1 ft³ = 1,728 in³) |
| 1 cubic yard | 0.764554857984 m³ | Volume (1 yd³ = 27 ft³) |
| 1 pound | 0.45359237 kg | Bag weights |
| 1 US short ton | 907.18474 kg | Weight (2,000 lb) |
| 1 tonne (metric ton) | 1,000 kg | Weight |
| 1 ton per cubic yard | 1,186.553 kg/m³ (1.186553 t/m³) | Density |
Gravel driveway calculator
Used by the gravel driveway calculator on the home page.
area = length × width
raw volume = area × depth
volume with allowance = raw volume × (1 + allowance % ÷ 100)
weight = volume with allowance × density
suggested order = weight rounded up to a whole ton or tonne
cost = (weight × price per ton) or (volume with allowance × price per cubic yard) + delivery
In two-layer mode each layer (base and surface) has its own depth, material, density, allowance and price, and the calculator applies the steps above to each, then adds them. Delivery is added once. Cost is shown only when every layer has a price. Switching between US and metric converts the numbers you have entered and shows a notice; prices are not converted, because a price per ton and a price per tonne are different amounts.
Tons to cubic yards calculator
Used by the tons to cubic yards calculator.
tons → volume: volume = weight ÷ density (no allowance added)
area covered = volume ÷ spread depth (optional)
volume → tons: weight = volume × (1 + allowance % ÷ 100) × density
suggested order = weight rounded up
Pea gravel calculator
Used by the pea gravel calculator.
rectangle area = length × width
circle area = π × diameter² ÷ 4
L-shape area = (length A × width A) + (length B × width B), two rectangles that don’t overlap
volume with allowance, weight and order as in the main calculator
bags = weight ÷ bag weight, or volume with allowance ÷ bag volume; shown rounded up and exact
coverage per ton = 1 ÷ (density × depth), before allowance
cost = exact weight × price per ton, or exact bags × price per bag, + delivery
The project list sets starting depths of 2 inches (5 cm) for paths and borders and 3 inches (7.5 cm) for patios. The play area preset is a starting value to edit: the depth needed under play equipment depends on fall height, and the page asks you to check current playground safety guidance.
Gravel driveway cost calculator
Used by the gravel driveway cost calculator.
from a known quantity: weight or volume as entered, the other derived with the density; no allowance added
from dimensions: volume with allowance and weight as in the main calculator
material = weight × price per ton, or volume × price per cubic yard
labour = weight × labour per ton
total = material + delivery + labour
Every price is your input. The calculator does not include site preparation, fabric, equipment hire or tax.
Gravel driveway depth calculator
Used by the gravel driveway depth calculator. It applies the main calculator’s steps to the same area at 2, 4, 6 and 8 inches (5, 10, 15 and 20 cm in metric). The allowance (default 10%) and density (default 1.40 tons per cubic yard) are editable and the same values are used for every depth, so the comparison stays like for like.
Gravel cubic yard calculator
Used by the gravel cubic yard calculator.
volume = length × width × depth (1 yd³ = 27 ft³)
optional allowance: volume × (1 + allowance % ÷ 100), default 0%
area covered by one unit of volume = 1 ÷ depth
Geometric volume only: no density or weight is applied.
Driveway base gravel calculator
Used by the driveway base gravel calculator.
base volume = length × width × thickness × (1 + allowance % ÷ 100)
base rock = base volume × density, order rounded up
fabric = length × width × (1 + overlap % ÷ 100)
Defaults: the road base preset (1.50 tons per cubic yard), a 15% allowance and 10% fabric overlap. All three are editable. The old version of this calculator fixed the density and overlap; they are now inputs.
Density values
Density turns volume into weight, so it has the largest effect on tonnage. The presets are planning defaults: typical values for each material, carried over from this site’s earlier published defaults. They are not taken from a single published standard and have no cited source. Real density varies with rock type, grading, moisture and compaction, so use your supplier’s figure when you have it; every calculator with a density lets you type your own. The metric values are exact conversions of the US values. The crushed concrete value is a placeholder until a sourced figure is available.
| Material | Tons per yd³ | Pounds per yd³ | Cubic yards per ton | Tonnes per m³ | Cubic metres per tonne |
|---|---|---|---|---|---|
| Crushed stone (#57) | 1.40 | 2,800 | 0.71 | 1.66 | 0.60 |
| Class 5 / road base / crusher run | 1.50 | 3,000 | 0.67 | 1.78 | 0.56 |
| Pea gravel | 1.35 | 2,700 | 0.74 | 1.60 | 0.62 |
| River rock / round gravel | 1.45 | 2,900 | 0.69 | 1.72 | 0.58 |
| Decomposed granite | 1.30 | 2,600 | 0.77 | 1.54 | 0.65 |
| Crushed concrete (recycled) * | 1.30 | 2,600 | 0.77 | 1.54 | 0.65 |
To catch typing mistakes, a density must be between 300 and 5,000 kilograms per cubic metre (about 0.25 to 4.2 tons per cubic yard).
Rounding
- Suggested order: rounded up to the next whole ton or tonne, because suppliers usually sell whole units and rounding down could leave you short. Tiny floating-point errors are removed first, so an exact 3 tons orders 3, not 4. Bags are rounded up the same way.
- Displayed values: rounded to 2 decimal places, half away from zero, for display only. Calculations keep full precision.
- Cost: worked out from the exact quantity, not the rounded order, and shown to the cent. The results say which quantity the cost uses.
- Suppliers may sell in other steps, such as half tons or full loads. Ask yours.
Waste and compaction allowance
The allowance is a percentage added for uneven ground, spreading losses and settling. It is applied to the volume once, before weight and cost are worked out. The default is 10% (15% in the base calculator, 0% in the cubic yard calculator). It is a planning choice, not a measured compaction rate; your supplier or contractor may suggest a different figure. Converting a weight you already have adds no allowance.
Limitations
- The calculators assume each area has a uniform depth. For curves and irregular shapes, split the area into rectangles (or use the pea gravel calculator’s circle and L-shape) and add the results.
- Results depend on your measurements and the density you use. The arithmetic cannot correct a wrong input.
- The calculators do not model soil, drainage, traffic loads or climate, so they cannot tell you which depth or base design your driveway needs. Depth and material guidance on this site is general planning information, not engineering advice.
- Costs are estimates built from the prices you enter. They are not quotes, and they leave out anything you don’t enter.
How the calculators are tested
The calculators and this site’s published numbers are checked by automated tests that run before each release. At the most recent run on 13 October 2026 every test passed:
- Unit tests: every unit factor; each calculator against hand-worked examples with the working written out; blank, zero, negative, text, very large and decimal inputs; the allowance applied exactly once; cost per ton, per cubic yard and per bag; tons to cubic yards and back.
- Invariants: the same driveway in US and metric gives the same weight to within 0.01%; results rise with every dimension; 0% allowance leaves the volume unchanged; an exact whole number is never rounded up.
- Content checks: every table on the site is generated from the calculator code, and every number in a worked example or answer is recalculated and compared.
- Browser tests: each calculator is used in a real browser by keyboard alone, at phone, tablet and desktop widths; errors are announced and linked to their field; results never show NaN or Infinity.
- Accessibility checks: every page is scanned with axe-core for WCAG 2.2 AA issues at phone and desktop widths.
Changelog
Site rebuild (TODO(owner): launch date)
- Rebuilt the site on WordPress. Every page keeps its address.
- New: pea gravel calculator (rectangle, circle and L-shape, with bags), the how many yards in a ton of gravel guide, and calculator and guide hub pages.
- The tonnage calculator now converts both ways and shows the area covered at a given depth.
- The main calculator can size a base and surface layer together, accepts a price per cubic yard or cubic metre as well as per ton, and includes delivery.
- Cost is now worked out from the exact quantity instead of the rounded-up order, and the results say so.
- Switching units now converts the numbers you entered instead of loading defaults.
- The depth and base calculators’ density and allowance are now editable; crushed concrete was added as a placeholder preset.
- Metric densities are now exact conversions of the US values (previously rounded, within 1%).
- Removed unsourced price ranges from the cost pages and guides; the cost guide’s two-layer example now gives 17 tons of base rock, matching the formula (it previously said 16).
3 October 2026
- Fixed a rounding error that could add an extra ton (and its cost) when a result was a whole number.
- Fixed a 1 sq ft overstatement in the fabric estimate.
- Very large inputs now show “–” instead of 0.00.
- Corrected the cost calculator’s description, a compaction example and one table value.
- Removed an unsourced lifespan claim.
- Added this methodology page and the author profile.
September 2026
- Site and calculators first published.
Report an error
Email contact@graveldrivewaycalculator.com with the page, the values you entered and the result you expected. Confirmed errors are fixed and recorded in the changelog above.