Online Calculators
A collection of online calculators for everyday math and projects: percentages and date differences, home-renovation estimates for paint, tile, concrete and wallpaper, plus ring and watch sizing.
Calculator
Basic and scientific modes, voice readout in 9 languages, large buttons and a running paper-tape — built to be easy for seniors, children and everyone else.
Percentage Calculator
Percent of a number, percent change, discount, tip, VAT, markup
Age Calculator
Free age calculator: your exact age in years, months, days, hours, minutes, seconds — plus next birthday countdown. Free, in-browser.
Date Difference Calculator
Days between two dates, business days and holidays
How Many Days Have I Lived
See exactly how many days you have lived since birth — with weeks, hours, a live counter, milestone dates and your life in weeks. Free.
Schengen 90/180 Calculator
Add your Schengen trips — see days used, days left and your must-leave date.
Hours Calculator
Free work-hours calculator: enter shifts with start, end and breaks, get weekly totals, overtime and pay. Export CSV. Free, in-browser.
Sleep Calculator
Free sleep cycle calculator: best bedtime to wake up rested, or when to wake if you sleep now. Age-based targets, nap timer, 90-min cycles.
Watch Size Calculator
Wrist → ideal case diameter, lug-to-lug, strap width
BAC Calculator
Estimate blood alcohol content via the Widmark formula: peak BAC, sober-up time, when you can legally drive. Free, in your browser.
Julian ↔ Gregorian
Convert dates between Julian (old style) and Gregorian (new style) calendars. Automatic shift per era, Orthodox feasts, Easter dates. Free.
Stair Calculator
Enter the floor-to-floor height and get the riser height, tread depth, stair angle and stringer length, with comfort and code checks.
Tile Calculator
Enter the room size and the tile size, add a waste margin, and get the number of tiles and boxes to buy.
Paint Calculator
Enter the room size, the number of coats and the paint coverage, and get the litres or gallons to buy.
Wallpaper Calculator
Enter the room size, the roll size and the pattern repeat, and get the number of rolls to buy.
Concrete Calculator
Enter the dimensions of a slab, footing or round column and get the concrete volume and the number of pre-mix bags.
Lumber Calculator
Enter the board thickness, width, length and quantity to get the board feet per board, the total and the cost.
Fence Calculator
Enter the fence length and post spacing to get the posts, sections, rails and pickets you need.
Running Pace Calculator
Enter a distance and the time it took to get your pace, speed and predicted race finish times.
Tire Size Calculator
Enter your original and new tire sizes to see the diameter change and how far the speedometer will be off.
GPA Calculator
Add each course with its letter grade and credit hours to get your credit-weighted GPA.
Depth of Field Calculator
Set your sensor, focal length, aperture and focus distance to see the depth of field and focus limits.
ND Filter Calculator
Pick the exposure without a filter and the ND filter you are using to get the corrected shutter speed.
Print Size Calculator
Enter the image pixel dimensions to find the print size at a chosen DPI, or the DPI at a target size.
Clothing Size Converter
Pick a category and your size in one region to see the matching size everywhere else.
