Gravel calculator

DIY complexity

Beginner

Spreading and levelling loose gravel needs only a rake and wheelbarrow — the main effort is physical (moving bulk material), not technical skill.

Introduction

This calculator estimates the volume, weight and purchase quantity of gravel needed for driveways, paths, sub-base layers under paving, drainage beds and decorative surface dressing. Because gravel compacts once it is spread, tamped or driven over, the loose volume a supplier delivers is always somewhat larger than the compacted in-place volume you actually need to fill — the tool lets you add a compaction allowance separately from ordinary waste to capture that difference. Grading matters too: a fine 10-20mm decorative or bedding gravel behaves differently from a coarse 40mm sub-base stone, and particle size affects both bulk density and how deep a layer needs to be to do its structural or drainage job properly. Supported uses include a structural sub-base under block paving or a driveway, a permeable drainage layer around foundations or land drains, and a loose decorative surface finish over landscape fabric. The tool sums the area of one or more measured zones, applies your chosen depth, converts the compacted volume to weight using an editable bulk density, and rounds the result up to whole bags or a bulk tonnage that respects your supplier's minimum delivery load. It cannot verify site drainage falls, the sub-base compaction standard required by a paving manufacturer, or vehicle access for a bulk delivery lorry — those still need to be checked on site.

Quick answer

For a 30 m² driveway sub-base at 8 cm depth with a bulk density of 1650 kg/m³, 5% waste, 15% compaction allowance and 3% moisture, the estimated weight is about 4925 kg (≈4.93 t) — roughly 198 bags of 25 kg, or about 5.0 t as a rounded bulk delivery.

Calculation methodology

01Measure each area to be covered as one or more zones (rectangle, circle, triangle, trapezoid or a hand-drawn shape) and subtract any excluded areas such as manholes or planting islands.
02Sum the net area of all zones and multiply each by its own depth to get a raw (theoretical) volume.
03Apply a waste percentage to cover spillage, over-excavation and irregular edges.
04Apply a compaction percentage separately, because gravel settles once tamped or trafficked, so more loose volume must be ordered than the finished compacted thickness implies.
05Convert the resulting volume to weight using the bulk density of the specific gravel grading you are buying, adjusted for a moisture percentage if the material will be wet at delivery.
06Round the weight up to whole bags, or to a bulk tonnage that respects the supplier's minimum delivery load, and compare the two purchase costs.

Formulas

volume_m3 = Σ(area_i × depth_i) × (1 + waste) × (1 + compaction)

Every measured zone's net area (after exclusions) is multiplied by its own depth and the results are added together into a raw volume. That raw volume is then inflated once for ordinary waste and once more for compaction, because gravel occupies more loose space than it will once tamped or driven over.

Variables

area_i = net area of zone i after exclusions (m²)
depth_i = layer depth entered for zone i (m)
waste = spillage and over-order allowance (%)
compaction = extra loose volume needed to reach the target compacted thickness (%)
volume_m3 = total volume to purchase (m³)

Rounding rule: This intermediate volume is not rounded; rounding is only applied later, once weight is converted into whole bags or a bulk tonnage.

Limitation: A single compaction percentage is applied uniformly across all zones; sub-base under a driveway and a shallow decorative topping often need different compaction rates, so run them as separate calculations if they differ significantly.

weight_kg = volume_m3 × density_kg_m3 × (1 + moisture); bags = ceil(weight_kg ÷ bag_kg); bulk_t = max(minimum_t, ceil(weight_kg ÷ 100) ÷ 10)

Volume is converted to weight using the bulk density of the specific gravel product, then increased for moisture if the load will be wet. The weight is rounded up to whole bags for small jobs, and separately rounded up to the nearest 0.1 tonne for a bulk order, with the supplier's minimum delivery load enforced as a floor.

Variables

density_kg_m3 = bulk density of the chosen gravel grading (kg/m³)
moisture = weight increase for wet material at delivery (%)
bag_kg = weight of one bag
minimum_t = supplier's minimum bulk delivery load (t)
bulk_t = bulk delivery quantity to order (t)

Rounding rule: Bags are always rounded up to a whole unit; bulk tonnage is rounded up to the nearest 0.1 t and then raised to the supplier's minimum delivery load if that minimum is higher.

Limitation: 1650 kg/m³ (or the 1600 kg/m³ generic default) is an editable example, not a fixed constant — actual bulk density depends on grading, angularity and moisture at the time of loading, so confirm it against your supplier's product data before ordering.

Inputs that matter

Depth per zoneDrives volume linearly; sub-base layers are typically far deeper than a decorative topping, so using the wrong depth for the use case is the single biggest source of error.
Bulk densityChanges directly with grading, angularity and moisture; a fine sand-like decorative gravel and a coarse crushed sub-base stone can differ meaningfully in kg/m³.
Compaction allowanceAccounts for the gap between loose delivered volume and the finished, tamped or trafficked thickness — leaving it at zero under-orders material for any load-bearing use.
MoistureWet gravel weighs more per cubic metre than dry gravel of the same grading, which changes both the weight estimate and the number of bags or bulk tonnage needed.
Bag size vs. bulk minimumSmall jobs are usually cheaper in bags; larger ones cross a threshold where bulk delivery becomes cheaper, but only once the supplier's minimum load is met.
Excluded areasManholes, tree pits, drain covers and planting islands inside a zone should be subtracted so they are not paid for and over-filled.

Worked examples

Small decorative gravel path, 10 m²

A garden path over landscape fabric: 10 m² zone, 5 cm depth, generic bulk density 1600 kg/m³, 10% waste, no compaction allowance and no moisture adjustment because the gravel is a dry decorative topping, not a trafficked sub-base.

Raw volume = 10 × 0.05 = 0.5 m³. With 10% waste and 0% compaction: 0.5 × 1.10 × 1.00 = 0.55 m³. Weight = 0.55 × 1600 × 1.00 = 880 kg. Bags (25 kg each): ceil(880 ÷ 25) = 36 bags.

0.5 m³ is the theoretical volume, 0.55 m³ is the quantity after waste, and 36 bags is the final purchase figure — three bags more than the exact 35.2 that 880 kg divided by 25 kg would give, because bags cannot be bought as fractions.

⚠ No compaction allowance was applied here because a shallow decorative topping is not tamped like a sub-base; if this path will also carry occasional vehicle traffic, add a compaction percentage and recalculate.

Driveway sub-base with compaction and moisture, 30 m²

A vehicle driveway sub-base: 30 m² zone, 8 cm depth, bulk density 1650 kg/m³ for this crushed stone grading, 5% waste, 15% compaction allowance and 3% moisture because the load is delivered slightly damp.

Raw volume = 30 × 0.08 = 2.4 m³. With 5% waste and 15% compaction: 2.4 × 1.05 × 1.15 = 2.898 m³. Weight = 2.898 × 1650 × 1.03 ≈ 4925 kg. Bags (25 kg): ceil(4925 ÷ 25) = 198 bags. Bulk: ceil(4925 ÷ 100) ÷ 10 = 5.0 t.

2.4 m³ is the theoretical compacted-thickness volume; 2.898 m³ is the loose volume to order once waste and compaction are added; 4925 kg (≈4.93 t) is the moisture-adjusted weight that drives both the 198-bag figure and the 5.0 t bulk figure.

⚠ 15% compaction is an editable planning assumption for this grading and target thickness, not a guaranteed outcome — actual settlement depends on the stone type and how it is tamped; verify with your sub-base design or supplier if the driveway must meet a paving manufacturer's specification.

Bag vs. bulk cost comparison, patio sub-base 15 m²

A patio sub-base: 15 m² zone, 10 cm depth, bulk density 1600 kg/m³, 10% waste, 15% compaction, no moisture adjustment. Bags cost 6.50 per 25 kg bag; bulk gravel costs 68 per tonne plus a 40 delivery fee, with a 1 t supplier minimum.

Raw volume = 15 × 0.10 = 1.5 m³. With 10% waste and 15% compaction: 1.5 × 1.10 × 1.15 = 1.8975 m³. Weight = 1.8975 × 1600 = 3036 kg. Bags: ceil(3036 ÷ 25) = 122 bags → 122 × 6.50 = 793. Bulk: ceil(3036 ÷ 100) ÷ 10 = 3.1 t → 3.1 × 68 + 40 = 250.80.

Buying bags for this quantity would cost roughly 793, while a 3.1 t bulk delivery including the flat delivery fee costs about 250.80 — bulk is clearly cheaper once the load comfortably clears the supplier's 1 t minimum. The calculator surfaces both totals so you can compare rather than defaulting to bags out of habit.

⚠ Changing the selected currency only changes the displayed symbol — it does not convert 6.50, 68 or 40 into a different currency's equivalent value. Enter current local supplier prices in the currency you have selected, and confirm sales tax and any delivery surcharge separately.

Reading the results

The result panel separates the net area you measured, the volume after waste and compaction, the estimated weight, and the final whole-unit purchase quantity in both bags and bulk tonnage — each figure is larger than the last for a specific reason, not a rounding inconsistency. Bag cost and bulk cost are shown side by side with the lower of the two highlighted, so you can see at a glance which route is cheaper for the quantity you need once your supplier's minimum delivery load is taken into account.

Common mistakes

Ordering only the theoretical (uncompacted) volume for a driveway or sub-base and leaving the compaction allowance at zero, resulting in a layer that is thinner than designed once trafficked.
Using a fine decorative gravel's bulk density for a coarse crushed sub-base stone, or vice versa — grading changes density enough to shift bag and bulk quantities noticeably.
Copying a depth used for a different project (e.g. mulch or bedding sand) instead of the depth actually specified for the sub-base or drainage layer being built.
Forgetting to subtract existing gravel or hardcore already in place when topping up or re-grading an area.
Ordering a small bulk quantity without checking the supplier's minimum delivery load, then being charged for far more material than needed — or paying an avoidable small-load surcharge.
Treating a single bulk density figure as valid for both dry and wet material, when moisture at delivery can shift the weight enough to change the bag count.

Adapting to your country

Gravel bulk density, bag sizes and terminology vary widely by country and grading — a 20 mm or 40 mm crushed stone, 'type 1' sub-base, pea gravel or decorative aggregate can all have different kg/m³ figures and are sold under different local names. Bag sizes are commonly 20-25 kg in much of Europe and 0.5-1 cubic foot bags or 50 lb bags in North America; bulk is typically sold by the tonne in metric markets and by the cubic yard or ton in imperial ones. Changing the selected currency only changes the displayed symbol — it does not convert the bag price, bulk price or delivery fee you entered, so re-enter current local supplier prices after switching currency. Confirm applicable sales tax and any small-load or long-haul delivery surcharge separately, since neither is built into the calculator's cost output, and always check your supplier's minimum bulk delivery quantity before assuming a small bulk order is possible.

Limitations and verification

This calculator produces a planning estimate, not a sub-base design, drainage calculation or supplier quotation. It does not verify site access for a delivery lorry, ground drainage falls, geotextile or edge restraint requirements, or the compaction specification required by a paving or drainage system manufacturer. Complex or sloped areas should be broken into separate measured zones, and depth and compaction figures should be confirmed against the actual sub-base or landscaping design before ordering. Always verify the bulk density, moisture condition and minimum delivery quantity with your chosen supplier before placing a bulk order.

Last reviewed: 2026-08-24

Frequently asked questions

Why does the calculator ask for compaction as well as waste?

Waste covers spillage and cutting losses; compaction covers the fact that gravel occupies more loose volume than it will once tamped or driven over. Skipping compaction under-orders material for any load-bearing sub-base.

What bulk density should I use?

The 1600-1650 kg/m³ range shown is an editable example for common crushed stone gradings, not a universal constant. Use the figure from your supplier's data sheet, since angularity, grading and moisture all shift it.

Does moisture really change how much gravel I need to order?

It changes the weight, not the volume — wet gravel is heavier per cubic metre than dry gravel of the same grading, which shifts the bag count and bulk tonnage even though the space it fills stays the same.

How much depth do I need for a driveway sub-base versus a decorative topping?

This varies by design and local ground conditions, but sub-base layers are typically much deeper than a thin decorative surface dressing. Use the depth specified by your paving design or sub-base engineer, not a generic figure.

Should I buy bags or a bulk delivery?

Small quantities are usually cheaper in bags; larger quantities usually become cheaper in bulk once you clear the supplier's minimum delivery load. Compare the bag cost and bulk cost the calculator shows side by side.

Does changing the currency convert the prices I entered?

No. Changing currency only changes the displayed symbol and formatting; enter current local supplier prices in the currency you select.

Is this estimate enough to order material directly?

It is a planning estimate. Confirm actual bulk density, compaction requirements, site access for a delivery vehicle and any local sub-base specification with your supplier or contractor before ordering.

What is the difference between the gravel and excavation calculators?

The gravel calculator estimates material to buy and deliver to fill a space; the excavation calculator estimates spoil volume and weight to remove from a space — they use the same zone-based area engine but represent opposite material flows.

Gravel calculator.

Measurement zones

Material and purchase

How to get a reliable estimate

Measure the site

Choose the right material data

Allow for real site conditions

Frequently asked questions