About How Much Do I Need?

How Much Do I Need? is a small collection of calculators for the practical question that comes up before almost every project: how much should I buy?

What the calculators do

Each calculator asks for a few measurements, then works out the answer with standard area and volume formulas. Alongside the result you'll see:

• The calculated quantity: the mathematical amount, with nothing added.
• The estimated amount to buy: the calculated quantity plus an adjustable allowance for waste, rounded up to the sizes things are actually sold in.
• The working: every step, with your numbers, so you can check it or redo it by hand.

How accurate are the results?

The arithmetic is exact, and unit conversions use the official definitions (for example, 1 inch = 2.54 cm and 1 US gallon = 3.785411784 litres). The answer can only be as good as the inputs, though, and real jobs vary. Paint coverage depends on the surface, gravel weight depends on the stone, and every room has its awkward corners. That's why the extras for waste are adjustable and explained, and why each page says what could change the result.

Use the results to plan and budget, then check final quantities with your supplier, manufacturer or installer. For structural work such as foundations and load-bearing slabs, follow a professional's specification and your local building codes.

Private by design

There are no accounts and no analytics, and nothing you type ever leaves your device. The site is a set of static pages, and every calculation happens in your browser. Once a page has loaded, it keeps working even if you go offline.

A few small ads from Adsterra keep the site free. They load in a separate, sealed-off frame that can't see the calculator, and they may use cookies. The privacy policy explains what that means and how to turn them off.

Feedback and source code

The site's source code is public on GitHub. If you spot a mistake in a formula, or there's a calculator you would find useful, please open an issue there.