Practical guides, how-tos and comparisons to get the most out of our free online tools.
A percentage is just a fraction out of 100. Put the number over 100, reduce to lowest terms, and handle decimal percentages like 12.5% by clearing the decimal first. With examples.
Lena Hoffmann · 3 min read
Kinetic energy is the energy of motion, given by KE = ½mv². Learn what the formula means, why speed matters most, and see worked examples in joules.
Lena Hoffmann · 4 min read
Use a recent race result and the Riegel formula to predict your finish time at a longer distance — from a 5K to a 10K or half marathon.
Aisha Karim · 4 min read
The golden ratio is roughly 1:16 — learn grams of coffee per cup and how to adjust strength to your taste.
Marco Bianchi · 4 min read
Battery size, efficiency, speed, cold weather and terrain all move an EV's real range far from the sticker figure. Here's how each factor works.
Marco Bianchi · 2 min read
Your basal metabolic rate is the energy your body burns at complete rest. Learn how the Mifflin-St Jeor equation estimates it and what raises or lowers it.
Sofia Nunes · 3 min read
Size a solar array from your annual electricity use, panel wattage, and local sun hours — plus a quick payback estimate in dollars.
Marco Bianchi · 3 min read
Estimate bricks for any wall from its area, a per-square-foot brick count, and a waste allowance — so you buy once and avoid a second trip.
Marco Bianchi · 3 min read
A year has roughly 260 weekdays before holidays. Learn where that number comes from, why it varies by country, and how public holidays bring it down to the working days you actually get.
Lena Hoffmann · 4 min read
Figure out a realistic car budget using the 20/4/10 rule, income limits, and total cost of ownership — not just the sticker price on the window.
Camille Laurent · 3 min read
See how many gigabytes per hour SD, HD, and 4K video use, and how to check a monthly streaming habit against a data cap.
Daniel Okonkwo · 4 min read
Add and subtract hours and minutes reliably. Learn to carry over 60, borrow when subtracting, and handle a result that crosses midnight into the next day.
Lena Hoffmann · 4 min read