Gravel Calculator

Understanding the Gravel Calculator

A gravel calculator converts area and depth into cubic yards and tons. The tonnage conversion uses a single density figure, and real gravel densities vary enough between materials that the same volume can differ by half a ton.

How it actually works

Enter length, width, and depth. The calculator multiplies for volume, divides by 27 for cubic yards, and multiplies by 1.4 to estimate tons. A 10 by 8 foot area at 3 inches deep gives 0.74 cubic yards and 1.04 tons.

The deeper context most people miss

The 1.4 figure sits at the upper end for most landscape gravel, so tonnage here may run slightly high for pea gravel and about right for crushed stone. Suppliers can give the density of their specific product, and asking is worthwhile on larger orders where a 10% difference is several hundred dollars.

How deep gravel actually needs to be

Depth requirements vary by application more than most people expect, and under-specifying is the usual error. Decorative ground cover in a border can work at 2 inches, purely for appearance and weed suppression. A garden path with foot traffic wants 3 to 4 inches over a compacted base. A driveway is a different proposition entirely: a properly built gravel driveway is typically constructed in layers, with a base course of larger angular stone at 4 to 6 inches, a middle layer, and a surface layer of smaller stone, giving a total depth of 8 to 12 inches over prepared subgrade. Building a driveway at 3 inches produces ruts within a season, because there is insufficient depth to distribute vehicle loads and the stone simply pushes into the subgrade. Drainage applications including French drains and soakaways have their own requirements driven by the volume of water to be handled. The other frequently overlooked factor is compaction. Loose delivered gravel settles considerably when compacted, and the reduction is commonly cited around 20% for angular crushed stone, so ordering the finished depth without allowance produces a shallower result than intended. For a driveway where compaction is deliberate and mechanical, ordering roughly 20 to 25% above the calculated volume is standard practice.

A worked example: a driveway rather than a path

The default 10 by 8 area at 3 inches gives 0.74 cubic yards and about a ton, which suits a small decorative area or a short path. Scale to a driveway of 40 by 12 feet built properly at 10 inches total depth and the arithmetic changes dramatically: that is 400 cubic feet, or 14.8 cubic yards, and at 1.4 tons per yard around 20.7 tons. Add 20% for compaction and the order approaches 25 tons, which is roughly two truck deliveries. At that scale several things become significant that do not matter for a path. Delivery is priced per load and per distance, so ordering in full loads is considerably more economical than partial ones, and a supplier will advise on their truck capacity, typically somewhere around 10 to 20 tons depending on vehicle. Access matters, since a large truck needs room to tip, and where access is restricted the material may need moving by barrow at substantial labour cost. Placement location matters too, since moving 25 tons of stone by hand is genuinely arduous and having it tipped as close as possible to the final position saves considerable work. Geotextile membrane beneath the stone is worth specifying on driveways, since it prevents the gravel migrating into the subgrade over time, which is the main mechanism by which gravel driveways thin and develop ruts.

Deciding which material to specify

Stone type affects performance more than price alone suggests. Angular crushed stone interlocks under compaction and stays put, which makes it the right choice for driveways, paths, and any surface bearing load. Rounded stone including pea gravel does not interlock, so it shifts underfoot and under tyres, migrates toward edges, and is difficult to walk on comfortably, making it suitable for decorative areas and drainage but a poor driveway surface despite its appearance. Stone size matters alongside shape: larger stone drains better and resists displacement but is uncomfortable underfoot, while smaller stone compacts firmer and is more comfortable but can migrate. Crushed stone with fines, sometimes called crusher run or hardcore, contains a range of particle sizes including dust that fills voids and compacts to a very firm surface, which is ideal as a base layer but drains poorly and is not usually a finish surface. Clean stone with fines washed out drains freely and is used where drainage is the point. Edging is worth budgeting for on any gravel area, since without a restraint the stone migrates outward continuously and the area thins from the edges inward. Weed membrane beneath helps, though it is less effective than often claimed since organic matter accumulates on top of the stone over time and weeds germinate in that layer regardless.

Why tonnage and volume both appear, and which suppliers use

Bulk materials are sold by weight in some markets and by volume in others, and the two are related by density, which varies by material, particle size, moisture content, and how tightly the material is packed. This creates several sources of confusion. Moisture is significant: wet stone weighs meaningfully more than dry stone of the same volume, so a ton delivered after rain contains less material than a ton delivered dry, which is a genuine consideration when buying by weight. Suppliers typically quote a density for their product, and using theirs rather than a generic figure improves accuracy on larger orders. Volume itself is ambiguous, since loose volume as delivered exceeds compacted volume in place, and the difference for angular stone is commonly around 20%. When ordering, being explicit about whether the quantity is loose or compacted avoids the situation where a delivered load looks generous and produces a thinner finished layer than expected. For smaller quantities, bulk bags typically hold around 0.5 to 0.8 cubic yards depending on supplier, and they are considerably more expensive per unit than bulk delivery, so the crossover to loose delivery arrives quickly, often around two or three bags. Bagged stone from a builders' merchant is more expensive still and suits only very small quantities or situations where access prevents bulk delivery.

Variations: applications, base layers, and related materials

Depth and specification vary by purpose. Decorative borders work at 2 inches, paths at 3 to 4 over a compacted base, patios and shed bases at 4 to 6 of compacted hardcore beneath the surface material, and driveways at 8 to 12 in layers. Drainage applications including French drains use clean angular stone without fines, wrapped in geotextile to prevent soil ingress, with the pipe bedded and surrounded. Soakaways are sized by the volume of water to be handled, calculated from roof or hard surface area and local rainfall, and are typically subject to building regulations. Related bulk materials calculated the same way include sand at similar densities, topsoil which is lighter and varies substantially with moisture and organic content, bark mulch which is much lighter at roughly 0.4 to 0.5 tons per cubic yard, and road base or MOT type 1 in the UK, which is a graded aggregate designed to compact to a firm base. Each has its own density, so applying a gravel figure to any of them produces error, and asking the supplier for theirs is the reliable approach.

Ordering gravel accurately

Specify depth by application rather than defaulting to a single figure: 2 inches for decorative borders, 3 to 4 for paths over a compacted base, and 8 to 12 in layers for a driveway carrying vehicles. Add roughly 20% for compaction, since loose delivered stone settles considerably and ordering the finished depth produces a shallower result. Ask your supplier for the density of their specific product rather than relying on a generic 1.4 tons per cubic yard, since materials vary and the difference matters on larger orders. Choose angular crushed stone for anything bearing load, since it interlocks under compaction, and reserve rounded stone such as pea gravel for decorative and drainage uses where its tendency to shift does not matter. Budget for edging, since without restraint the stone migrates outward and the area thins from the edges. Consider geotextile membrane beneath driveways to stop stone migrating into the subgrade. And order in full delivery loads where possible, since partial loads carry disproportionate delivery cost.

What people get wrong

• Ordering the finished depth without a compaction allowance, when loose stone settles around 20% and the result is a thinner layer than intended.
• Using pea gravel or other rounded stone for a driveway, when it does not interlock, shifts under tyres, and migrates toward the edges continuously.
• Building a driveway at path depth, when vehicle loads require 8 to 12 inches in layers and a shallow build develops ruts within a season.
• Applying a single density figure to any bulk material, when topsoil, sand, and bark mulch differ substantially and bark is roughly a third the weight of stone.

Where the math comes from

Cubic yards = Length × Width × (Depth in inches / 12) / 27, since a cubic yard is 27 cubic feet. Tons = Cubic yards × 1.4, using an approximate density for crushed stone. Actual densities vary by material, particle size, and moisture content, typically from around 1.25 for pea gravel to 1.4 for crushed stone, with lighter materials such as bark mulch nearer 0.4 to 0.5.

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