Standard Calculator: Basic Arithmetic, Memory and Percent
What the standard calculator does The standard calculator is a free browser calculator for everyday arithmetic: addition, subtraction, multiplication, division, percent, square root, squares, reciprocals and a five-key memory row. Everything runs locally; nothing you type is uploaded.
Like a pocket calculator, each operator key finishes the calculation already on screen: 2 + 3 × 4 = gives 20 , not 14. For typed expressions with mathematical precedence, use the scientific calculator .
The display keeps 16 significant digits and rounds longer fractions to 10 decimal places (1 ÷ 3 = reads 0.3333333333 ); results at or above 10¹⁶ switch to scientific notation.
How to use it 01 Enter the first number with the keypad or the keyboard (digits, ., the four operators, %, Enter, Backspace, Escape). 02 Pick an operator. The current value moves up to the expression line, for example 240 ×. 03 Enter the second number and press `=`. The result replaces the display, and the last 50 calculations stay in the history list. 04 Use the function row √ square root, x² square, 1/x reciprocal, ± sign flip, CE clears the entry, C clears everything except memory and history.05 Store with the memory row: MS stores, MR recalls, M+/M- adjust the most recent value, MC clears it.Worked examples Every result below was produced by this calculator; type the same keys to reproduce it. For the memory walkthrough, enter 36, press MS, C, then 20, M+, MR → 56 .
Keys
Display
Why
2 + 3 × 4 =20 + completes first: (2 + 3) × 4
1 ÷ 3 =0.3333333333 10-decimal display rounding
240 × 15 % =36 % with no pending operator: 15 ÷ 100
200 + 10 % =220 % with a pending +: 10% of 200
81 √9 square root
0.1 + 0.2 =0.3 stored sum 0.30000000000000004, rounded
0.1 + 0.2 - 0.3 =5.5511151231e-17 full stored values carry
9007199254740992 + 1 =9007199254740992 beyond 2⁵³ − 1
The percent, square-root and memory keys The percent key follows two rules:
With a pending + or -, % takes a percentage of the pending base : 200 + 10 % = → 220 , and 80 - 25 % = → 60 .
With ×, ÷, or nothing pending, % divides the entry by 100: 240 × 15 % = → 36 , and 15 % displays 0.15 .
√ applies to the display and chains (81 √ → 9 , 9 √ → 3 ); 1/x divides 1 by the display. Negative roots, a reciprocal of zero and division by zero stop with an error; C or a new digit restarts. Memory is a small stack: MS stores, MR recalls the latest value, M+/M- adjust it.
Where it fits Bills and tips A $42.60 bill with a 15% tip: 42.6 + 15 % = reads 48.99 ; ÷ 3 = splits it into 16.33 each.
Discounts and counts A jacket marked 25% off at $96: 96 - 25 % = → 72 , the price before tax; ten percent more off gives 64.8 . Twelve boxes of 24 units is 12 × 24 = → 288 units.
Assumptions and limits Immediate execution. The keypad has no parentheses and no precedence: 2 + 2 × 2 = is 8 here, not 6. Typed precedence belongs to the scientific calculator .
Display rounding. 16 significant digits with at most 10 decimal places means 1 ÷ 3 can never be exact.
No unit tracking. Metres times metres gives a bare number, and nothing is converted.
Memory is per page. Reloading or closing the page clears memory, history and errors.
Errors fail fast. Division by zero and undefined roots show an error, never ∞ or NaN.
Integer and range limits. Integers are exact up to 2⁵³ − 1 (9,007,199,254,740,991); above that, adding 1 may change nothing. Results above about 1.8 × 10³⁰⁸ overflow to ∞. Floating-point rounding Numbers are stored in IEEE 754 binary64, the format used by browsers, spreadsheets and most programming languages. 0.1 is stored as 0.1000000000000000055511151231257827…, so 0.1 + 0.2 is stored as 0.30000000000000004440892098500626… and displayed as 0.3 . Because stored values carry between steps, 0.1 + 0.2 - 0.3 = reveals a small remainder, 5.5511151231e-17 . That is honest binary arithmetic, not a keypad mistake. For money, count in cents or round the final answer deliberately.
Questions Does the standard calculator follow order of operations? No. It evaluates each operator as it is pressed: 2 + 3 × 4 = is 20 , not 14. The scientific calculator parses precedence.
Why does 0.1 + 0.2 show 0.3 when the stored value is bigger? The display keeps 16 significant digits, hiding that artifact. Subtract 0.3 afterwards and the remainder appears.
How do I take a percentage of a number? Use × with %: 240 × 15 % = gives 36 . To raise or lower a base by a percentage, use + or -: 200 + 10 % = gives 220 .
References
IEEE, IEEE 754-2019 — IEEE Standard for Floating-Point Arithmetic , standards.ieee.org （访问日期：2026-09-30）— binary64 format, rounding and special values.
Ecma International, ECMAScript Language Specification : Number type （访问日期：2026-09-30）— double-precision semantics and shortest number printing.
MDN Web Docs, Number.MAX_SAFE_INTEGER （访问日期：2026-09-30）— why integers are exact up to 2⁵³ − 1.
David Goldberg, What Every Computer Scientist Should Know About Floating-Point Arithmetic , ACM Computing Surveys 23(1), 1991, docs.oracle.com （访问日期：2026-09-30）— the rounding behind the 0.1 + 0.2 example.
Privacy All input and calculation run inside your browser and are never uploaded. The text on this page is static and records no user input.
Sources & review
Reviewed by CalcX Editorial Team
Updated 2026-09-30