Pro Calculators and Guides
How to Add and Subtract Time: Days, Hours, Minutes and Seconds
Add or subtract durations such as 2 h 45 min and 1 h 30 min, and see totals in hours, minutes and seconds. Useful for work hours, travel and cooking.
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Pro Calculators and Guides
Specialist calculators are only useful when you understand the rules behind the numbers. These guides explain what each professional calculator does, which inputs matter, how to read the result and where the official rules come from, covering payroll and tax, immigration and visas, housing, business compliance, engineering and science. Every guide links to a free tool that runs in your browser and keeps your figures private.
318 guides
Pro Calculators and Guides
How to Add Blank Pages to a PDF (Start, End or Between Pages)
Insert empty pages into a PDF for notes, double-sided printing or signatures. Free, in your browser, no upload.
Pro Calculators and Guides
How to Add Line Numbers to Any Text (Paste and Copy)
Put a number in front of every line of your text, with a custom start and style. Useful for code, poems, contracts and references.
Pro Calculators and Guides
How to Add, Subtract, Multiply and Divide Fractions (With Mixed Numbers)
A clear method for fraction arithmetic and a calculator that shows the simplified fraction, mixed number and decimal.
Pro Calculators and Guides
How to Blur Faces and Number Plates in a Photo Before You Share It
Hide faces, number plates, addresses and screenshot details by blurring or pixelating areas of an image. Free, in your browser.
Pro Calculators and Guides
How to Calculate a Tip and Split the Bill Between People
Work out 10, 15, 18, 20 or 25 percent tip and see what each person pays, with a quick method you can do in your head.
Pro Calculators and Guides
How to Calculate Area, Perimeter, Surface Area and Volume of Common Shapes
Formulas and a calculator for rectangles, circles, triangles, cubes, cylinders, spheres and more, with unit tips.
Pro Calculators and Guides
How to Calculate College GPA on the 4.0 Scale (Semester and Cumulative)
Turn letter grades and credit hours into a semester GPA and a cumulative GPA with a simple weighted-average method.
Pro Calculators and Guides
How to Calculate Floor Area and How Many Tiles You Need
Work out the floor area of a room and the number of tiles to buy, with extra for cutting and breakage. A simple method with examples.