The first question to ask when planning a path, patio, bed or driveway is, how much gravel do I need? Get out measurements, pick a depth, calculate volume into volume in weight or bags, and add allowance. This guide describes the metric and imperial calculations without providing the densities of suppliers as universal.
Fast Easy Solution: Use Four Steps to compute Gravel Needed.
Measure area in metres squared or feet squared. Volume = area (finished depth) Area (finished depth): Multiply area and depth using the same units. The estimate of weight is volumes x supplier bulk density. Percentages such as simple, well-edged areas: 5% or irregular shape, settlement and spillage and compaction: 10%. An arithmetic calculation of the size of gravel is automated by a gravel calculator or a gravel quantity calculator, and the input counts.
| Volume equals area multiplied by depth. Weight equals volume multiplied by bulk density. Bags required equals total volume divided by volume per bag, rounded up. |
Measure the Surface Area by Shape
Rectangular and Square Areas
For a rectangle, area equals length multiplied by width. A 6m by 4m bed covers 24m²; a 20ft by 12ft patio covers 240ft². Squares use the same formula. Measure inside permanent edging so the gravel required for area is not overstated.
Figure 1. A rectangular outdoor area being measured before surface coverage is calculated.
Circular and Triangular Areas
In the case of a circle, the radius = half diameter and 3.1416 (area of a circle) = radius 2. Since it is a triangle, the base x perpendicular and divide by 2. Use not the sloping side as height.
Fressed Lines and asymmetrical Buildings.
In case of a curvilinear one multiply length of centre by average width. Change changing widths into short segments and add them all up. In the case of irregular landscaping, divide the outline into triangles, semicircles and rectangles; make the calculations of each, and deduct the ponds or planters and add up the numbers. Any estimate of the calculator of the coverage of gravel is enhanced by a grid sketch and a number of measurements.
Choose Depth and Calculate Volume
Divide depth by multiplying: 1,000 of millimetres equals 1 metre; 1,000 of inches equals 1,000 of feet. Thus, 50mm becomes 0.05m, while 2in becomes 0.1667ft. A computation of gravel depth must be based upon a finished compacted depth, rather than the loose height in a delivery pile.
| Finished depth | Typical application | Coverage from 1m³ | Coverage from 1yd³ |
| 25mm or 1in | Decorative top-up | 40m² | 324ft² |
| 50mm or 2in | Beds and light paths | 20m² | 162ft² |
| 75mm or 3in | Busy paths and patios | 13.3m² | 108ft² |
| 100mm or 4in | Driveway surface or base | 10m² | 81ft² |
Depth changes volume directly: doubling depth doubles weight, bags, and material cost. Coverage assumes an even layer. Particle shape, grading, compaction, moisture, and the sub-base can change actual yield.
Figure 2. Trail construction showing a top material positioned over a gravel base layer.
Convert Volume into Weight, Bags, and Cost
Ask for the product’s loose bulk density. Decorative gravel usually ranges between 1.4 to 1.7 tonnes per cubic metre although the quoted value is used. For example, 2m³ at 1.6t/m³ weighs about 3.2t. Imperial suppliers could charge 2,400-2,900lb/cubic yard. These ranges are not global.
In the case of bags, divide required volume (or weight) by stated yield (or divide required weight by bag weight with density the same). Round upward. Cost = tonnes, cubic yards or bags x unit price plus delivery, tax, membrane or edging.
| Convert | Operation |
| Metres to feet | Multiply by 3.28084 |
| Square metres to square feet | Multiply by 10.7639 |
| Cubic metres to cubic yards | Multiply by 1.30795 |
| Inches to metres | Multiply by 0.0254 |
| Cubic feet to cubic yards | Divide by 27 |
| Tonnes to pounds | Multiply by 2,204.62 |
Five Worked Gravel Examples
Rectangular Garden Bed
A 6m by 4m bed at 50mm depth needs 6 × 4 × 0.05 = 1.20m³. Adding 5% gives 1.26m³. At 1.6t/m³, order approximately 2.02t, subject to the supplier’s density and minimum load.
Circular Flower Bed
Figure 3. A circular gravel rock garden bounded by masonry edging.
An 8ft diameter bed has a 4ft radius. Area is 3.1416 × 4² = 50.27ft². At 2in depth, volume is 8.38ft³, or 0.31yd³. With 10% allowance, plan for 0.34yd³.
Garden Pathway
A curved path 12m long and averaging 1.2m wide covers 14.4m². At 60mm depth it needs 0.864m³; adding 10% produces 0.95m³. This demonstrates gravel per square metre changing with depth.
Patio
A 20ft by 15ft patio covers 300ft². At 3in depth it needs 75ft³, or 2.78yd³. Add 5% and the order becomes 2.92yd³. Gravel per square foot equals 0.25ft³ here.
Small Driveway
A 10m by 3m driveway with a 100mm compacted layer needs 3m³. Adding 10% gives 3.3m³. At an indicative 1.7t/m³, that is 5.61t; confirm layer design, density, and compaction with the supplier.
Frequently Asked Questions
How much gravel do I need per square metre?
At 50mm depth, one square metre needs 0.05m³. Multiply by density for weight and include the chosen allowance.
How much gravel per square foot at two inches?
One square foot at 2in depth needs 0.1667ft³, so one cubic yard theoretically covers about 162ft².
Should I order by volume or weight?
Use the supplier’s sales unit. Convert volume to weight only with that product’s current bulk density.
How much extra gravel should I order?
Allow roughly 5% for regular edged work and 10% for curves, uneven ground, compaction, or handling loss.
Does compacted depth differ from loose depth?
Yes. Loose gravel settles under vibration and traffic. Tell the supplier your required finished depth and compaction method.
How do I calculate gravel bags?
Divide total required volume by stated bag coverage, then round up. Check whether coverage assumes a particular depth.
Can one density suit every gravel type?
No. Stone type, particle size, grading, shape, and moisture affect bulk density; supplier data is preferable.
What should I subtract from an irregular area?
Subtract measurable spaces receiving no gravel, including buildings, large planters, drains, ponds, and fixed paving.
Conclusion: How Much Gravel to Order
Measure, find area by shape, multiply by, compacted depth, convert with supplier density, plus an allowance. Prior to determining the quantity of gravel to be ordered, determine bag yield, load increments, delivery charges, and a separate sub-base is needed. Regard results as approximations until density and coverage is verified.