Gravel Calculator

Gravel Calculator: Driveways, Landscaping and Aquariums

This gravel calculator has two modes because two very different people are looking for it. For landscaping projects like a driveway, path, or flower bed, choose landscaping. This is how suppliers sell it in cubic yards and tonnes. Select “Aquarium” if you are putting up a gravel calculator fish tank. You will get pounds of substrate that is the right size for your tank’s footprint instead of its gallon capacity. 

Since the math behind those two jobs is very different, this gravel calculator yards splits them up in the same way so they don’t get mixed up into general advice that doesn’t help either. Part 1 talks about gravel for the garden. It includes cubic yards, tons, driveway layers, pea gravel, and full metrics for people in the UK. Part 2 talks about aquarium substrate in its own unique way.

Outdoor Gravel: How Much Do You Need? (Cubic Yards)

Everything outdoors starts with volume. Get your cubic yards first, then convert to tons for the supplier.

Cubic yards = (Length ft × Width ft × Depth in inches ÷ 12) ÷ 27

Worked example: a 40 ft × 10 ft driveway at 4 inches deep

Step 1. Convert the depth: 4 ÷ 12 = 0.333 ft

Step 2. Multiply: 40 × 10 × 0.333 = 133.3 cubic feet

Step 3. Divide by 27: 133.3 ÷ 27 = 4.94 cubic yards

Yards of gravel calculator: the divide-by-27 step

That last step catches people out, so here is where the 27 comes from. A yard is 3 feet. A cubic yard is a cube 3 feet on every side, and 3 × 3 × 3 = 27 cubic feet.

Measure in feet, and your answer is in cubic feet. Suppliers sell in cubic yards. Divide by 27 and you have bridged the gap. If your number looks wildly too big, you skipped it.

Quick coverage reference: what one cubic yard covers

Always add extra. Gravel settles and spreads. Add 10 percent for a simple top-up job and 20 percent for anything you plan to compact, since compaction squeezes real volume out of the pile. Our 4.94-yard driveway becomes about 5.9 yards once you allow for compaction, so you would order 6.

Doing the base layers for a slab or patio at the same time? Our concrete calculator and topsoil calculator use the same divide-by-27 method.

Converting Yards to Tons (Gravel Calculator Tons)

Here is where a lot of orders go wrong. You calculated volume, but almost every supplier sells by weight.

Tons = Cubic yards × Density

Crushed stone commonly runs about 1.4 tons per cubic yard, though figures between 1.3 and 1.6 are all in normal use depending on the rock.

Worked example: converting the driveway above

4.94 cubic yards × 1.4 = 6.9 tons

Typical densities by material

Density is not a fixed constant. It changes with the parent rock, the stone size, and how wet the pile is. Limestone is lighter than granite. Larger stones leave bigger air gaps between them, which lowers the weight per yard.

So do this before you order: work out your cubic yards on this page, then call the supplier and ask for their tons-per-yard figure for the exact product you want. Plug their number in, not a generic one. On a 6 ton order, the difference between 1.4 and 1.6 is nearly a ton of stone, which is real money and a real gap in your driveway.

Gravel Driveway Calculator: Depth and Layers

A proper gravel driveway is not one depth of one material. This is the most expensive mistake on this page.

A driveway that will hold up under cars needs 4 to 6 inches total, built in two layers:

• Base layer: 4 inches of angular crusher run or dense-grade aggregate. Angular stone locks together and carries the load. Rounded stone does not.
• Top layer: 2 inches of a finer decorative stone such as #57 or pea gravel.

Worked example: the same 40 ft × 10 ft driveway, done properly

Area: 40 × 10 = 400 sq ft

Now look at what most people order and see how it compares. It looks like a 4-inch driveway, so they order 6.9 tons of it. They are short 4 tons and have to leave the road unfinished because it needs about 10.9 tons of work over two products.

On top of that, pack it down. When you roll the base layer, it loses about 20% of its open volume. When you order the base, leave 20% extra room. The real order is now getting closer to 12 tons.

Check that your delivery truck can get to the site and that you have a place to dump 12 tons of stone. This seems like a no-brainer, but we often forget to do it. That much weight is about twice as much as a small car.

Pea Gravel Calculator: Why It’s Different

Pea gravel is more than just small pieces of broken rock. If you use assumptions about crushed stone to figure out pea gravel, you will get the wrong answer twice.

There are two changes:

1. How dense. Because pea gravel calculator is round and smooth, there is more space between the stones. It weighs about 1.3 to 1.4 tons per cubic yard, while dense-grade base stone weighs about 1.5 to 1.6 tons per cubic yard.
2. Depth. Because it’s just for looks and not for support, it’s laid less deeply, generally 2 to 3 inches. Because those round stones never fit together, a thick layer just moves and makes ruts when it’s pushed.

Worked example: a 200 sq ft pea gravel patio at 2 inches deep

Step 1. Convert the depth: 2 ÷ 12 = 0.167 ft

Step 2. Volume: 200 × 0.167 = 33.3 cubic feet

Step 3. Cubic yards: 33.3 ÷ 27 = 1.23 cubic yards

Step 4. Tons: 1.23 × 1.35 = 1.7 tons

Don’t use it in driveways where cars can turn or on slopes that aren’t mild. Stones that are round roll. Exactly as the sections above say, put pea gravel on a drive as a thin top layer over compacted angular ground to get the look you want. Pea gravel moves into lawns and flower beds without edges, so they are always helpful.

Gravel Calculator UK: Tonnes, Cubic Meters and Bulk Bags

Gravel calculators are bought in different sizes and in different ways in the UK, Australia, and Canada, so these numbers are not just a renaming of the US numbers.

Cubic metres = Length m × Width m × Depth m

Millimeters are often used to measure depth. So, 100 mm is equal to 0.1 m, which is 1,000 split by 100. There is no step to divide by 27 because suppliers already use cubic meters.

Worked example: a 12 m × 3 m drive at 100 mm deep

Step 1. Volume: 12 × 3 × 0.1 = 3.6 cubic metres

Step 2. Tonnes, at roughly 1.6 tonnes per cubic metre: 3.6 × 1.6 = 5.76 tonnes

Step 3. Bulk bags, at 800 kg each: 5.76 ÷ 0.8 = 7.2, so order 8 bulk bags

What is actually different

A handy UK rule of thumb: one 800 kg bulk bag covers about 10 square meters at 50 mm deep. For anything past roughly 4 or 5 bulk bags, loose-tipped delivery by the tonne usually works out cheaper than bagged.

To move between systems: 1 cubic meter = 1.31 cubic yards and 1 tonne = 1.1 US tons. The unit toggle on the calculator handles this for you.

PART 2: Aquarium Gravel Calculator (Fish Tank Substrate)

Welcome to the other half of this page. Everything above is irrelevant here. You are not buying by the ton, you are buying bags by the pound, and the number that matters is your tank’s footprint, not its gallon rating.

Two ways to work it out. Use the second one.

The rough rule: about 1 to 1.5 lbs of gravel per gallon of tank capacity. A 20-gallon tank lands at 20 to 30 lbs. Quick, but it can be well off, because tanks of the same volume have very different floor areas. A tall tank and a long tank both holding 20 gallons need different amounts of substrate.

The footprint method (accurate):

Cubic inches = Tank length × Tank width × Substrate depth Pounds = Cubic inches ÷ 18

That divide-by-18 shortcut comes from aquarium gravel weighing roughly 95 lbs per cubic foot, and a cubic foot being 1,728 cubic inches.

Worked example: a standard 20-gallon tank at 2 inches deep

A 20-gallon high has a footprint of about 24 in × 12 in.

Step 1. Cubic inches: 24 × 12 × 2 = 576

Step 2. Pounds: 576 ÷ 18 = 32 lbs

So buy 30 to 35 lbs, which is usually two standard 15 or 20 lb bags. That matches the rule-of-thumb range, and it will match less well on unusually tall or unusually wide tanks.

Quick reference by tank size

Measure your own tank rather than trusting the table. Footprints vary between manufacturers, and a “20 gallon long” has a completely different floor than a “20 gallon high.”

How deep should you go?

• Fish-only tank: 1 to 2 inches. Not too deep, just the right depth to look good and hold good bacteria. A gravel vacuum can actually clean it.
• Planted tank: 2 to 3 inches. Root tabs and roots need a place to sit and go.
• Deeper than 3 inches: be careful. Thick, undisturbed layers of fine substrate can form oxygen-deficient pockets that turn hydrogen sulfide into hydrogen gas. Fine sand packs down, but coarse grit is better at handling depth.

Three practical things before you pour it in

1. Rinse it. New aquarium gravel carries dust that will cloud your tank for days. Put it in a bucket, run water through it, and stir until the water runs clear. Do it outside if you can, and never rinse it with soap.
2. Slope it back to front. Run it slightly deeper at the back. It looks better and it makes waste collect at the front where you can see and remove it.
3. Add it before the water. Put the gravel in the empty tank, then fill slowly onto a plate or your hand so you do not blast craters into it.

Rescaping an existing tank? Do not replace all the substrate at once. Your beneficial bacteria live in there, and swapping the lot can restart your cycle. Change it in halves, a few weeks apart.

FAQs

Q1. How many tons of gravel do I need for a driveway?

Find the number of cubic yards first, then multiply it by the density. A 40-foot-by-10-foot driveway that is 4 inches deep takes up 133.3 cubic feet, which is 4.94 cubic yards. At 1.4 tons per cubic yard, that’s 6.9 tons. To account for settling and compacting, add 10 to 20 percent. Also, check with your source to make sure of the density, as it changes depending on the type of stone.

Q2. How deep should gravel be for a driveway?

Four to six inches all together, made of two layers instead of one. As a base, pack down 4 inches of angular crusher run. Then, put 2 inches of finer ornamental stone on top. You should figure out the two layers separately, since people often run out of several tons of a product when they only order one 4-inch layer.

Q3. Is pea gravel calculated differently from regular gravel?

There are two ways to answer yes. Because the stones are rounder, there is more air space between them, so it weighs about 1.3 to 1.4 tons per cubic yard instead of 1.5 to 1.6 tons for dense-grade base stone. It also goes down less deeply, only 2 to 3 inches instead of 4 to 6 inches, because it is just for looks and doesn’t fit together like angular stone does.

Q4. How is gravel sold in the UK?

Not by the US ton and cubic yard, but by the ton and the cubic meter. The small amounts come in bulk bags that hold about 800 kg, and the bigger orders come loose-tipped by the ton. About 1.6 tons per cubic meter, and a bulk bag that is 50 mm deep will cover about 10 square meters.

Q5. How much gravel do I need for a 20-gallon fish tank?

A 2-inch bed weighs about 30 to 35 pounds. The footprint of a 20-gallon high is about 24 by 12 inches, so 24 by 12 by 2 equals 576 cubic inches, and 576 by 18 equals 32 pounds. Cut it in half to about 16 pounds for a 1-inch bed. Check your own tank’s size because they are not all the same.

Q6. How deep should aquarium gravel be?

If you only have fish in the tank, one to two inches is enough depth to keep bacteria alive and still be able to vacuum properly. With two to three inches of space between the plants, the roots can grow. If you go deeper than 3 inches with fine substrate, oxygen-depleted areas could form in the bed. So, don’t go deeper than that unless you have a good reason and plan for it.

Conclusion

One page, two jobs, and two sets of math. How many tons does your supplier actually sell? Measure your area outside, figure out the cubic yards, and then multiply by the density. The 40×10 driveway was 4.94 yards deep at one point and weighed 10.9 tons when it was made correctly in two layers. This is the exact amount of space that people run out of in the middle of a job. When you’re inside, forget about yards and tons.

Find the floor of your tank and choose a depth of 1 to 2 inches for fish or 2 to 3 inches for plants. Then, divide the number of cubic inches by 18 to get pounds. It weighed 32 pounds for the 20-gallon tank. The gravel calculator at the top of this page can help you with that. Make sure you’re in the right mode before you type anything, and only place one order instead of two.