Which calculator for which situation
- Restaurants and bars. Bill split and tip handle the table; change checks what comes back.
- Shopping. Discount for the final price; unit price to find which package actually costs less — the larger one is not always cheaper per ounce.
- Driving. Fuel economy measures your real mpg; trip cost projects fuel and tolls; EV charging estimates time and cost.
- Home and work. Energy use turns watts into dollars on the bill; hours worked closes a timesheet; reading time estimates how long a text takes.
- Miscellaneous. Number to words for cheques and contracts; random picker and dice for decisions; dog age and love calculator for fun.
Two calculations almost everyone gets wrong
Unit price: the bigger package is not always cheaper. The "buy more, pay less" instinct fails often, particularly on family-size promotions. The honest comparison is always per ounce, millilitre or unit — and there is a second question the arithmetic does not ask: whether you will use it all before it expires. A quantity discount is only a discount if you were buying that quantity anyway.
Fuel economy: the number on the sticker is not yours. Published figures come from standardised test cycles. Real consumption varies with tyre pressure, load, air conditioning, terrain and driving style — differences of 15% to 20% from the rated figure are ordinary. Measuring your own is the only way to know the number that matters for a trip budget.
Energy use: where the bill actually goes
An appliance costs power (kW) × hours of use × rate. What the formula makes clear is that high power used briefly usually matters less than low power used continuously. A 1,500 W space heater run for an hour a day costs less monthly than a 150 W refrigerator running around the clock — which is why replacing an old fridge saves more than shortening any single high-power habit.
Frequently asked questions
How do I measure my car's real fuel economy? Fill the tank, reset the trip odometer, drive normally and fill up again. Divide the miles driven by the gallons of the second fill. One measurement means little; three give a reliable average.
Is the electricity rate just the price per kWh? No. Delivery charges, taxes and seasonal adjustments sit on top. For a realistic estimate, divide your total bill by the kWh consumed — that is the rate you actually pay.
Why write amounts in words? Because it protects against alteration: on a cheque, the written amount prevails over the numerals if the two disagree.