How to Calculate Average Speed
How to calculate average speed: divide total distance by total time. 150 km in 2 hours is 75 km/h. Learn why you cannot just average two speeds.
Travel
Dates & Time
What Day of the Week Were You Born?
What day of the week were you born? Use an age calculator, or the Doomsday algorithm by hand. Includes a worked example and century anchor days.
Dates & Time
How Many Weeks Are in a Year (and a Month)?
How many weeks are in a year? 52 weeks plus 1 day (2 in a leap year). Learn why, when a year has 53 weeks, and how many weeks are in a month.
Dates & Time
How to Calculate Business Days Between Dates
How to calculate business days between dates: subtract weekends and public holidays from the total. Includes a worked example and a quick estimate.
Home & DIY
How Much Wallpaper Do You Need?
How much wallpaper do you need? Divide total wall area by about 5 square metres per roll and round up. Covers the drop method and pattern repeat.
Home & DIY
How Much Mulch or Topsoil Do You Need?
How much mulch do you need? Multiply bed area by depth for cubic feet, divide by 27 for cubic yards. Worked example, depths, and a coverage rule.
Home & DIY
How Much Flooring or Tile Do You Need?
How much flooring do you need? Find the room area, add 10% for waste, and divide by the coverage per box. Includes a worked example and waste guidance.
Home & DIY
How to Calculate Square Footage of a Room
How to calculate square footage: multiply length by width in feet. A 12 by 10 room is 120 sq ft. Covers whole houses, L-shaped rooms, and conversions.
Math & Education
How to Round Numbers (and Significant Figures)
How to round numbers: if the next digit is 5 or more round up, otherwise round down. Covers decimal places, significant figures, and the exactly-5 case.
Math & Education
How to Calculate Percentage Increase and Decrease
How to calculate percentage increase and decrease: multiply by (1 + decimal) or (1 – decimal). Worked examples, plus the increase-then-decrease trap.