A Unit Converter Built on Exact Decimal Math

10 categories, 79 units

The free tier isn't a demo: 13 everyday units are free forever, with no ads. Exactly which ones is worth stating plainly, because most apps won't — metre, kilometre, centimetre, millimetre, foot and inch for length; kilogram, gram, milligram and pound for mass; and all three temperature scales. Premium unlocks the remaining 66 units and the other seven categories for a single $2.99 payment.

Reading a converted number correctly

A converter that shows more digits than the input justifies is quietly lying. Converting "6 feet" to metres gives 1.8288 m exactly, because the foot is defined as 0.3048 m — that figure is exact, not rounded. But converting a measurement you eyeballed as "about 6 feet" to four decimal places implies a precision you never had. The arithmetic here is exact to 18 digits so the tool is never the source of error; deciding how many of those digits are meaningful is still yours.

Temperature is the one to watch, because it is the only category here with an offset rather than a simple ratio. Twice 10 °C is not 20 °C in any physical sense, and a 5-degree difference converts differently from a 5-degree reading. The converter handles readings, which is almost always what you want.

Which conversions the free tier actually covers

Those 13 units cover the conversions most people reach for daily: metric to imperial length for DIY and furniture, kilograms to pounds for luggage and shipping, and Celsius to Fahrenheit for weather and cooking. What they don't cover is professional work — no acres or hectares for land, no psi or bar for pressure, no kWh or BTU for energy, no KiB/MiB/GiB for storage. That split is deliberate: the everyday cases are free, and the categories you only need if converting is part of your job are the paid ones.

One consequence worth knowing before you install: miles and yards are premium. If your main use is running distances, that is the paid tier, not the free one.

Why exact math matters in a converter

Most converters run on floating-point arithmetic, which quietly mangles the last digits of a conversion. CalcBoard converts with decimal arithmetic at 18-digit precision, and temperature uses exact formula conversion rather than lookup approximations. What you see is the real number.

Convert in one panel, calculate in the next

The converter is a full panel mode, so the classic engineering workflow finally fits on a phone: convert 72 °F in one panel, use the Celsius result in a formula in the next panel, and keep a running total in a third. Results appear as you type, and the swap button flips the conversion direction instantly.

Frequently Asked Questions