Practical calculators for daily life

Planning numbers, not exact bills

The tools in this section answer everyday questions, and most of them mix two kinds of input. Some numbers are exact: the price on a receipt, the liters on a pump display, the servings a recipe makes. Others are estimates: the fuel economy your car will manage on a trip, the hours a heater will run, how strong a scaled-up spice blend will taste. The arithmetic is always exact, but an answer can only be as good as its least certain input.

That shapes how to read the results. A tip split or a unit price comparison uses figures you already have, so the answer is the real number. A trip or electricity cost is a forecast. It is useful for comparing options, setting a budget or deciding whether something is worth it, but the final figure comes from the pump, the meter or your bill. When an estimate matters, measure the uncertain input yourself: a full-tank fuel check, a plug-in energy meter or a test batch tells you more than any published rating.

The results are for everyday planning. They are not financial, tax or legal advice, and they do not replace the instructions that come with an appliance or a recipe.

Choosing units that match your source

Most of these calculators accept several unit systems, and the safest choice is the one your source uses. If a recipe is written in grams, scale it in grams; if the pump sells liters, enter liters. Converting first and calculating second adds a rounding step for no benefit. A few units share a name but not a size, which is where most errors come from:

Fuel economy has its own twist: liters per 100 km measure how much fuel a distance takes, so a lower number is better, while miles per gallon and kilometers per liter measure how far a quantity of fuel goes, so a higher number is better. The calculators handle the conversion, but it helps to know which way round a figure works before you type it in.

Money needs no conversion at all. Every amount on these pages is a plain number, so enter prices in your own currency and read the results in the same one.