The home improvement calculators on this page all solve the same problem. You measure in feet, your supplier quotes in tons or cubic yards, the bags on the shelf are labeled in pounds, and the number you phone through is not the number you meant. They close that gap before the delivery truck turns up, which is the point at which a mistake stops being fixable.
Each one shows its working rather than just handing you a figure, so you can check it against your own measurements and see where the number came from.
Gravel Calculator
For driveways, paths, patio bases and drainage trenches. Enter length, width and depth, pick your material, and it returns cubic yards, tons and a material cost with the standard 10 percent allowance already added.
The reason it matters is the unit mismatch. Gravel is calculated by volume and sold by weight, and one cubic yard weighs roughly 1.4 to 1.7 tons depending on the stone. Order 19.5 tons when you meant 19.5 cubic yards and you will take delivery of about two thirds of a driveway, which you tend to discover around the halfway point.
It also flags the delivery minimum, which catches people on small jobs. Most suppliers will not deliver under 10 cubic yards and the better rates start around 15.
Concrete Calculator
For slabs, footings, steps and post holes. It handles both rectangular pours and round holes, so a patio and a 20 post fence line both work, and it tells you how many bags that volume comes to at four different bag sizes.
The useful part is the comparison it runs underneath. Bags look like the cheap option on a small job and they are, but only up to about 0.8 cubic yards, which is roughly 65 square feet at 4 inches thick. Past that the truck wins and the gap widens quickly. It also warns you when a full 10 yard load would cost no more than the smaller order you were about to place.
Using Them Together
Most concrete jobs need both. A slab poured straight onto soft ground will crack no matter how thick it is or how good the mix was, so a compacted sub base of around 4 inches sits underneath almost everything.
That means two separate orders from two different suppliers, in two different units, usually on different days. Work out the gravel first, because it has to go in and be compacted before the concrete arrives, and because the sub base depth changes how deep you need to dig.
For a 20 by 10 patio that is roughly 2.7 cubic yards of sub base gravel and 2.7 cubic yards of concrete, which is a neat coincidence rather than a rule. Change the slab thickness and the two numbers separate quickly.
What These Calculators Will Not Do
Home improvement calculators give you quantities and rough material costs. They do not quote your job.
Prices for both gravel and concrete are intensely local, because neither material travels far economically. Two suppliers 30 miles apart can quote very differently for the same thing, so treat the cost figures as a sanity check on a quote rather than a substitute for getting three.
They also stop at materials. Excavation, reinforcement, forms, geotextile fabric, labor and disposal of the spoil are all real costs on these jobs and none of them are in the numbers. If you want the full picture on concrete specifically, our guide to concrete cost per yard breaks down where the money actually goes, including the short load fees most people do not see coming.
More home improvement calculators are being added here. Asphalt, paint coverage and square footage are next.