Last Modified: April 4, 2024

Gravel Calculator

Don't Get Caught Short On Project Day

Close up of limestone gravel

By Ben Parrot - Landscape Gardener & Amateur Geologist


Welcome to our guide all about how to calculate the quantity of aggregate you will require for your next landscaping project. A reasonably accurate aggregate calculation is always necessary for estimating the approximate volume of construction aggregate or decorative aggregates needed to complete a landscaping job. Therefore, getting the initial calculations right is essential to the success of the entire project. It's for this reason that we strongly advocate using an online decorative aggregate calculator.

The good news is that getting an accurate estimate of how much gravel is required using a gravel calculator is straightforward. You just need the intended dimensions – length and width of the area – and the proposed depth of the aggregate to get the likely volume. Alternatively, you can also calculate it yourself using our formulas.

Measuring an area for gravel calculator

In this article, we provide you with access to our unbiased and free aggregates calculator. We cover the process and formulas for manually calculating the aggregate quantity required for a project with a few methods. Also included is some handy information about converting the raw volume number into a cost estimate and tips for measuring up. So, pump up the volume, pump up the volume, let's go!

Oh, and don't forget to explore our 'Pebble Picker' tool, located in the sidebar or menu. This allows you to effortlessly select and compare various decorative aggregates, based on their colour and type.

Gravel Calculator Key Takeaways

Pen and a ruler on drawing plans


MOT: In construction, "MOT" typically stands for "Ministry of Transport." This term is often used in the UK to refer to a type of crushed aggregate, commonly known as "MOT Type 1," approved by the Ministry of Transport for use in road and driveway base layers due to its durability and compactability.

Aggregate: a material or structure formed from a mass of loosely compacted fragments or particles.

For our intents and purposes, aggregate is a word used to cover the many different types of materials used in landscaping an outdoor design, whether slate chippings, MOT subbase gravel, ballast or even pebbles. Decorative aggregates are collections of materials, generally stones, wood or other, used in design to create aesthetic features—the calculator on this page is designed for people planning to landscape their garden.

Pea gravel close up

Importance of Aggregate Calculations in Project Planning

Making an accurate aggregate calculation is essential to successful project planning. It's the only way to ensure you order the correct quantity of aggregates needed for a project. Accurate estimations are the best way of preventing wastage or shortages that could disrupt timelines and cost estimate-based budgets. For example, when mixing concrete, it is crucial to order enough materials for sufficient ballast coverage to achieve strength in the concrete mix.

Saying that, often a rough estimate can be more than adequate for more straightforward aesthetic features, such as a slate mulch bed featuring chippings. So, if you're just after a rough guide on the approximate volume of gravel a specified area would need, take a look at our table below.

Coverage Area

3cm/1.2in Depth

4cm/1.6in Depth

5cm/2in Depth

6cm/2.4in Depth

1m² or 11ft²

4 Maxi Bags (80kg)

5 Maxi Bags (100kg)

6 Maxi Bags (120kg)

7 Maxi Bags (140kg)

5m² or 54ft²

15 Maxi Bags (300kg)

25 Maxi Bags (500kg)

1 Bulk Bag (~850kg)

1 Bulk Bag (~850kg)

10m² or 108ft²

1 Bulk Bag (~850kg)

1 Bulk Bag (~850kg)

2 Bulk Bags (~1.7ton)

2 Bulk Bags (~1.7ton)

25m² or 269ft²

2 Bulk Bags (~1.7ton)

3 Bulk Bags (~2.5ton)

3 Bulk Bags (~2.5ton)

4 Bulk Bags (~3.4ton)

For bigger, or more complex areas, it's important to calculate the volume of gravel accurately, as using the right amount can significantly improve your project's look, stability, and durability. Factors such as achieving the desired drainage, load-bearing capacity, and overall functionality of the gravel or other aggregates, including sub-bases for areas with traffic, can become problematic if not properly considered.

However, whether you are intent on calculating your needs manually or using an online aggregate calculator, starting with the correct measurements is key, so let's start there.

Tips on Measuring the Area

Accuracy in measurements and calculations is vital to ensuring your area measurements for project planning and avoiding errors when ordering the materials. However, it is more than achievable with the right tools and approach.

The minimum you will need:

  • Suitable measuring tool (see below)
  • Pencil/pen
  • Sketch pad
  • Someone to help you
  • Pegs or heavy brick (if you can't get help)
Making notes of measurements

Start With a Skeleton Plan

To accurately measure the area of a proposed garden feature, start with a skeleton plan, defining its approximate shape and breaking down complex shapes into simpler geometric forms, such as rectangles, triangles and circles.

Use a measuring tape, measuring tape wheel or laser measure tool to obtain the dimensions for the desired length, width, and diameter (if applicable). Record them on your skeleton plan as you work your way around the shape's perimeter. There are also online tools which can help simplify the process.

Measuring tape wheel

How to Calculate the Gravel Cover Required for an Area

As the old adage goes, a carpenter always measures twice and cuts once. Measuring a small piece of wood is often much simpler than a garden expanse, so we will cover a few techniques for you budding landscape architects.

Manual Aggregate Volume Calculations

While most simple shapes can be pretty easy to calculate with the right formula manually, we are all prone to human error. A small error can lead to inaccurate results, inconvenience and even costly mistakes. For those of you who prefer the to be your own aggregate calculator, here are the formulae.

For a Metric Gravel Calculator

For metric, to calculate how much gravel is required, measure the length and width in metres and multiply by the desired depth in centimetres. Then, divide by 1,000 to determine the quantity of cubic meters needed.

Use the appropriate area formula based on the shape, then multiply by the depth:

  • rectangles (length × width),
  • triangles (0.5 × base × height),
  • circles (π × radius²).

For irregularly shaped designs, as mentioned earlier, divide them into sections, calculate each area volume, and then sum them for the amount of gravel you will need.

Simple Imperial Volume Calculation in Cubic Yards

To accurately calculate the amount of gravel needed for a given area, in imperial, measure the length and width of the site in feet and then multiply these dimensions by the desired depth of gravel in inches. Then, divide the result by 324 to obtain the required cubic yards.

Irregular shaped front garden with white pebbles

Types of Aggregate Calculators

There are many types of aggregate calculators online today. Our calculator will work in place of all of the following types:

  1. 1
    MOT Type 1 Calculator: An MOT 1 calculator is used to determine the amount of MOT Type 1, which is a type of crushed stone and gravel that is often used as a subbase for roads, driveways, and other construction projects. See below.
  2. 2
    Subbase Calculator: A sub-base calculator determines the amount of subbase material needed for a construction project. Subbase material refers to the layer of material that is placed on top of the soil and beneath the concrete or asphalt surface.
  3. 3
    MOT Calculator: A MOT calculator helps you estimate the amount of MOT required for a construction project. MOT stands for Ministry of Transport and refers to a type of crushed stone and gravel that meets certain specifications for use in construction projects.
  4. 4
    Ballast Calculator: A ballast calculator helps you estimate the amount of ballast needed for a construction project. Ballast refers to a coarse stone, gravel, or other material placed on top of the subbase layer and beneath the railway tracks or other constructions.
  5. 5
    Gravel Calculator: A tool used to calculate the amount of gravel needed for a specific project. Gravel is a type of rock commonly used in landscaping, construction projects, and road building.
  6. 6
    Stones Calculator: A tool used to calculate the amount of stones needed for a specific project. Stones come in various shapes and sizes for use in landscaping and construction projects.
  7. 7
    Slate Chippings Calculator: A slate chip calculator is used for calculating the volume of slate chippings you will need to complete a slate feature. 
Sub base calculator tool

Introducing the Gravel Calculator Tool

A gravel calculator is a tool that aids in estimating the quantity of gravel required for a landscaping project. It works by taking inputs such as the area's dimensions and desired depth, then using relevant formulas to calculate the volume of gravel needed, significantly simplifying the planning process by providing accurate measurements and preventing over or under-ordering of materials.

Now go ahead, have some fun!

Outdoor Aggregates Gravel Calculator



(excluding delivery)

The results are based on the average weight of a bulk bag of gravel or slate chippings: ~850kg per cubic metre.

Please keep in mind that this average can generally apply to standard bulk bags of approximately 1㎥. Checking the suppliers' sizing before ordering may also be advisable.

Gravel Calculator Summary

Calculating the volume of decorative aggregates required for your project can be efficiently accomplished using online tools or mathematical formulas. Online calculators provide user-friendly interfaces where you input your measurements and receive instant volume estimations, while manually employing formulas can be more prone to human error. Whichever method you choose, accurate measurements are pivotal to success. By utilizing these tools or formulas, you can more confidently determine the precise quantity of decorative aggregates needed and ensure your project achieves the desired goals without wastage or shortage.

Filling in a gravel path


What depth of gravel do I need?

You would usually lay a 10mm aggregate at a depth of 30-40mm, but this would need at least 50mm on a driveway. A 20mm aggregate would need to be at least 40-50mm deep and at least 50-60mm on driveways. A larger aggregate will settle and bond together better than smaller ones.

Example gravel estimate

We estimate an area of 5 metres by 5 metres, with a depth of 40mm, would require approximately three bulk bags of aggregates, slate chippings or gravel.

How do you convert aggregate in tonnes to ㎥?

When converting a tonne to m3, it's essential to start by identifying the aggregate's density, which can vary between 1.5 to 2.5 tons per cubic meter, depending on its type and moisture content. Once you have the density, the conversion can be done using the formula: Cubic Meters = Tons / Density (Tons/㎥).

For instance, if you have 10 tons of aggregate with a density of 2 tons per cubic meter, the calculation would be 5 cubic meters.

Can you use the gravel calculator for all aggregates?

You can utilize a gravel calculator for most gravel and aggregates, excluding pebbledash, resin-bonded aggregates, and rubber chippings. For these specific materials, it's best to contact the supplier directly to estimate the required quantities for your project.

How much gravel do I need for my garden?

To determine the total volume of gravel needed for your garden, you must start with an estimate of the approximate area to cover and depth. Gardens often pose a challenge for measuring due to their often irregular shapes. As a practical solution, we recommend extending the area into a simple square shape, just for the purposes of estimation.

Although the resulting estimate may be a little larger, ordering more aggregates is generally wiser than falling short. Having to reorder because you came up short can be very problematic because you may not be able to get more of the same aggregate that is consistent with your initial purchase. Also, a second order will incur extra costs associated with the need for a re-delivery.

What should I do if my landscaping area is an irregular shape?

For irregularly shaped designs, as mentioned earlier, divide them into sections, calculate each area volume, and then sum them for the amount of gravel you will need.

How to calculate how much slate chippings I need?

The best way to calculate the amount of slate needed is to measure up the area and then or use our slate chippings calculator to get an accurate estimate to work from.

How much aggregate do I need?

To calculate the amount of aggregate needed, you will need to determine the length, width, and depth of the area you want to fill. Once you have these measurements, you can use an aggregate calculator or a formula to determine the amount of aggregate you need in cubic metres, yards or tonnes.

There are many other, wonderful types of outdoor aggregates worth considering for your project. Check out them out!

About the author 

Ben Parrot is a landscape gardener and amateur geologist. He is the founder of Outdoor Aggregates, with the mission to create the first encyclopaedia for decorative aggregates. From natural stone through to decorative bark, these aggregates are critical to garden and landscape design, universally.

The problem: There isn't any place where all the different types of decorative landscaping materials and construction aggregates can be found, nor are the specifications of each type readily available. So, enriched by his extensive experience, and inspired by the timeless elegance and raw beauty of stone and rock, etched by nature's artistry over millennia, Outdoor Aggregates was born.