Frequently asked questions

The calculator is in radian mode. sin 30° = 0.5, but 30 radians is about 1,719°, and its sine is −0.988. Tap DEG/RAD above the display until it shows DEG. Kalkuli remembers your choice next time. If you're not sure which you need, this guide has a simple rule.

There are two versions. The sample standard deviation divides by n − 1; the population one divides by n. The statistics calculator shows both. In Excel, STDEV.S is sample and STDEV.P is population; the old STDEV function is the sample version. The worked example explains which to use.

There are several accepted ways to calculate quartiles. Kalkuli interpolates between ranked values, the same as Excel's QUARTILE.INC, Google Sheets and R. Many school courses use the "median of each half" method instead, which can give slightly different answers for small datasets. Neither is wrong.

It divides the number before it by 100, so 15% is 0.15 and 200 × 15% is 30. To add 15% to 200, type 200 × 1.15 or 200 + 200 × 15%. Some shop calculators treat 200 + 15% as 230, but that shortcut isn't standard maths notation, so Kalkuli doesn't do it.

It's scientific notation. 6.02E23 means 6.02 × 10²³, and 1.5E-7 means 1.5 × 10⁻⁷ = 0.00000015. You can type numbers in this form too. Kalkuli switches to E notation for numbers of a trillion (10¹²) or more and for numbers smaller than a millionth (10⁻⁶).

Powers are worked out before the minus sign is applied, so −2² means −(2²). This is the standard convention in algebra (it's why −x² is always negative or zero). For 4, type (-2)².

Kalkuli treats the hidden multiplication in 2(1 + 2) exactly like ×, and division and multiplication are worked left to right: (6 ÷ 2) × 3 = 9. Some people and some older calculators give implicit multiplication higher priority and get 1. The expression is genuinely ambiguous as written; use brackets to say what you mean.

The inverse keys can only return one value, so they give the principal value: −90° to 90° for sin⁻¹ and tan⁻¹, 0° to 180° for cos⁻¹. Whether another angle also fits depends on your problem. In triangles this is the "ambiguous case", which the triangle solver detects and shows both answers for.

Kalkuli calculates with about 16 significant digits and shows 12. The real limit is almost always your input data: if a length is measured to 3 significant figures, the answer is only good to about 3 as well. See significant figures and rounding, and the precision guide for what happens inside the computer.

Yes. Digits and ., the operators + - * / ^, brackets, ! and % all work. Enter calculates, Backspace deletes the last character (or the whole function name), Esc clears. You can also type function names directly, such as sqrt(2), log(1000) or pi.

Yes. Everything is calculated in your browser and nothing you type is sent anywhere. Your history and angle setting are saved only in your own browser's storage; "Clear all" in the History panel removes them. The privacy policy has the details, including how advertising cookies work.

Please get in touch with what you typed and what you expected. I check every report, and fixes are listed in the change log on the About page.