Plan gravel or mulch without hiding the assumptions

Use the Gravel & Mulch Calculator to combine up to three measured areas and estimate how much material to order at the installed depth you need. The result includes adjusted volume, estimated weight, full bags, bulk loads and an optional delivered-cost estimate.

The calculator supports US customary and metric measurements. It keeps density, compaction, waste, pack size, truck capacity and pricing visible so you can replace planning defaults with supplier information instead of treating one generic result as exact.

How to use the calculator

1. Choose US customary or metric units.
2. Enter the first measured area and add a second or third area when the project has separate beds or zones.
3. Enter the intended installed depth.
4. Choose gravel, crushed stone, wood mulch, bark mulch or a custom material.
5. Review the loose bulk density and replace it with supplier data when available.
6. Open the ordering settings to adjust compaction, waste, bag volume, bulk-load capacity, prices and delivery.
7. Compare the adjusted order volume with the bag and bulk breakdown before purchasing.

Optional areas can remain at zero. Every area uses the same selected unit system and installed depth, so calculate sections separately when they require different depths.

What the result shows

The main result is the adjusted order volume in cubic yards or cubic metres. Supporting results show:

• Total measured area
• Estimated material weight in US tons or metric tonnes
• Full bags required based on the entered bag volume
• Full bulk loads required based on the entered load capacity
• Installed volume before compaction and waste allowances
• Delivered cost based on either bag pricing or bulk pricing

Bag and load counts are rounded up to whole units. Volume, weight and cost values are rounded for display, but the supplier's actual sales increments remain the practical ordering constraint.

How gravel and mulch volume is calculated

The calculator first adds the entered areas and converts them to square metres. It converts depth to metres, then calculates the installed volume:

Installed volume = total area × installed depth

Compaction and waste are applied sequentially:

Order volume = installed volume × (1 + compaction %) × (1 + waste %)

Applying the allowances sequentially means a 5% compaction allowance and a 10% waste allowance produce a combined multiplier of 1.155, not 1.15. This keeps the calculation transparent and avoids disguising two different planning assumptions as one number.

The adjusted volume is converted to cubic yards for US results or kept in cubic metres for metric results.

Estimating material weight

Weight depends on the loose bulk density entered in kilograms per cubic metre:

Estimated weight = adjusted order volume in m³ × loose bulk density

The calculator starts with planning densities of 1,600 kg/m³ for gravel, 1,500 kg/m³ for crushed stone, 400 kg/m³ for wood mulch and 350 kg/m³ for bark mulch. Custom material starts at 1,200 kg/m³. These are editable assumptions, not supplier specifications.

Moisture, grading, particle shape, source and handling can materially change bulk density. Use a product data sheet, weighbridge record or supplier figure when weight affects vehicle capacity, delivery or structural decisions.

Bags versus bulk loads

The bag estimate divides adjusted volume by the entered bag volume and rounds up. US bag size is entered in cubic feet and metric bag size in litres. The starting assumptions are 2 ft³ or 50 L per bag.

The bulk-load estimate divides adjusted volume by the entered load capacity and rounds up. The starting assumptions are 5 yd³ for US customary projects and 4 m³ for metric projects. Change these values to match the actual product and vehicle.

A full-load count is a capacity planning result, not a promise that every supplier will dispatch that exact volume. Payload limits may be reached before nominal volume capacity when dense gravel is transported.

Bag, bulk and delivery cost

Choose whether cost should be calculated from full bags or from bulk volume. Bag cost multiplies the rounded bag count by the entered price per bag. Bulk cost multiplies adjusted cubic yards or cubic metres by the entered unit price. The delivery charge is then added to the selected material cost.

Enter all price values in the same currency. Prices and delivery start at zero so the calculator does not invent a market rate. Taxes, minimum-order rules, part-load fees, unloading, access constraints and labor are not separate inputs.

Verified examples

With the US starting values, 100 ft² at 3 inches deep has an installed volume of 0.93 yd³. Applying 5% compaction and 10% waste produces an order estimate of 1.07 yd³. At the gravel planning density, that is about 1.44 US tons, 15 full 2 ft³ bags or one 5 yd³ load.

A tested multi-area example combines 100 ft², 50 ft² and 25 ft² at the same 3-inch depth. The adjusted result is 1.87 yd³, about 2.52 US tons, 26 full 2 ft³ bags or one 5 yd³ load. At $4.50 per bag plus $30 delivery, the delivered estimate is $147.00. At $60 per yd³ plus the same delivery charge, the bulk estimate is $142.29.

With the metric starting values, 10 m² at 7.5 cm deep has an installed volume of 0.75 m³. After the starting allowances, the order estimate is 0.87 m³, which equals 18 full 50 L bags or one 4 m³ load.

Measurement and ordering limits

Enter nonnegative areas and make sure their total is greater than zero. Installed depth and bag or load capacity must be positive. The calculator accepts loose bulk densities from 10 to 3,000 kg/m³ and compaction and waste allowances from 0% to 50%. Prices and delivery cannot be negative.

Results are planning estimates. Uneven ground, variable depth, settling, moisture, contamination, compaction method, bag fill, truck payload, supplier rounding and product standards can all change the material actually required. Confirm measurements, density, product coverage, pack sizes, delivery limits and access conditions before ordering.

Frequently asked questions

How do I combine several garden beds?

Enter each measured bed as Area 1, Area 2 or Area 3. The calculator adds them before applying the shared depth and material settings. If the beds need different depths, calculate them separately.

Is compaction the same as waste?

No. Compaction allows extra loose material for settling or densification, while waste allows for spillage, grading variation and other losses. The calculator keeps them separate and applies compaction before waste.

Should I buy bags or bulk material?

Use the bag and bulk results as a quantity comparison, then apply the supplier's pack sizes, minimum orders, load capacities and delivery terms. Cost alone may not reflect handling, access or vehicle payload constraints.

Why can the weight estimate change without changing volume?

Volume comes from area, depth and allowances. Weight also depends on loose bulk density, which varies substantially between gravel, crushed stone and mulch and can change with moisture and grading.

Is the displayed decimal an exact purchase quantity?

No. The calculator rounds results for readability. Order in the increments your supplier actually sells and keep a practical buffer that fits the project conditions.