Calculator

Online scientific calculator

This free online calculator handles both basic arithmetic and scientific functions. It supports addition, subtraction, multiplication, division, as well as trigonometric functions (sine, cosine, tangent in degrees), square roots, powers, logarithms (base 10 and natural), and mathematical constants like pi and e.

All calculations run entirely in your browser with no data sent to any server. The calculator maintains a history of your computations so you can review and reuse previous results. It responds to keyboard input for fast, efficient calculation.

Keyboard shortcuts

• 0–9 and decimal point (.): Enter numbers directly from your keyboard.
• + - * /: Basic arithmetic operators.
• Enter or = : Evaluate the current expression.
• Backspace: Delete the last entered digit or operator.
• Escape: Clear the current calculation and start fresh.

Order of operations: PEMDAS / BODMAS

When a calculation contains more than one operation, the order in which those operations are carried out determines the result. The rules go by two common acronyms: PEMDAS (used in the United States) and BODMAS (used in the UK and many other countries). Both describe the same priority sequence: Parentheses / Brackets first, then Exponents / Orders, then Multiplication and Division left-to-right, and finally Addition and Subtraction left-to-right.

Consider the expression 2 + 3 × 4. If you read it left-to-right and add first, you get (2 + 3) × 4 = 5 × 4 = 20. That is wrong. Multiplication has higher priority than addition, so the correct evaluation is 2 + (3 × 4) = 2 + 12 = 14. This calculator follows standard operator precedence automatically, so entering 2 + 3 * 4 and pressing = returns 14, not 20.

If you genuinely want to add first and then multiply, use parentheses: type (2 + 3) * 4 via the keyboard and the calculator evaluates the bracketed group first, giving 20. Parentheses are not available as on-screen buttons, but you can type ( and ) directly from your keyboard whenever you need to control the order of evaluation.

Worked example: mixed operations

Suppose you want to calculate how much you owe after splitting a restaurant bill. The food cost £48, there is a 10% service charge, and you are splitting equally among 3 people. One way to express this is (48 + 48 * 0.10) / 3. The calculator evaluates it as: 48 * 0.10 = 4.8 first (multiplication before addition), then 48 + 4.8 = 52.8, then 52.8 / 3 = 17.6. Each person owes £17.60. Without the parentheses around the addition, you would get 48 + (4.8 / 3) = 48 + 1.6 = 49.6, which is incorrect.

Scientific functions explained

Trigonometric functions (sin, cos, tan) compute ratios of right triangle sides. This calculator uses degrees, not radians. The inverse functions (typically available as second-function keys) return the angle from a ratio. Logarithm base 10 (log) finds the power of 10 that produces a number, while natural logarithm (ln) uses base e (approximately 2.71828).

The square root function finds the number that, when multiplied by itself, produces the input. The power function (x squared or x to the y) raises a number to an exponent. The reciprocal function (1/x) divides 1 by the input, useful for parallel resistance calculations and other reciprocal relationships.

Everyday uses for an online calculator

A free online calculator handles far more than homework or office spreadsheets. Here are some of the most common real-world calculations people reach for a calculator to solve.

• Restaurant tips: Multiply the bill by a decimal to find the tip amount. A 15% tip on a £42 bill is 42 * 0.15 = 6.3, so £6.30. For 20%, use 42 * 0.20 = 8.4.
• Shopping discounts: To find the sale price after a 30% discount on a £85 item, calculate 85 * (1 - 0.30) = 85 * 0.70 = 59.5, so £59.50. Alternatively, find the saving first: 85 * 0.30 = 25.5, then subtract: 85 - 25.5 = 59.5.
• Splitting bills and costs: Divide the total by the number of people. If a holiday rental costs £1,260 for 7 nights shared among 3 guests, each person pays 1260 / 3 = 420 per night total, or 420 / 7 = £60 per night.
• Simple interest: To find the interest earned on savings of £5,000 at 3.5% per year for 2 years, calculate 5000 * 0.035 * 2 = 350.
• Unit conversions: Convert miles to kilometres by multiplying by 1.60934. Convert pounds to kilograms by dividing by 2.20462.
• Flooring and area: Multiply length by width to find the area of a room. A room 4.5 m × 3.2 m requires 4.5 * 3.2 = 14.4 square metres of flooring.

Common mistakes and how to avoid them

Even simple calculators trip people up in predictable ways. Knowing these pitfalls in advance saves frustration.

• Ignoring operator precedence: The most frequent error is expecting left-to-right evaluation when mixed operators are involved. If you type 10 + 5 * 2, the result is 20, not 30, because multiplication is evaluated first (5 * 2 = 10, then 10 + 10 = 20). Use parentheses whenever the intended grouping differs from standard priority rules.
• Chaining operators without evaluating: Pressing an operator key when a result from a previous operation is already pending can overwrite or chain the expression unexpectedly. When in doubt, press = to get a clean result before starting the next calculation.
• Floating-point surprises: Because this calculator uses JavaScript's IEEE 754 double-precision arithmetic, some decimal results contain tiny rounding noise. For example, 0.1 + 0.2 may display as 0.30000000000000004. This is a property of binary floating-point, not a bug. For financial work requiring exact cent-level precision, round your final result to two decimal places.
• Negating a number: The +/− button flips the sign of the number currently shown on the display. It does not act as a subtraction operator between two numbers. To subtract, use the − operator button.
• Trig functions expect degrees: The sin, cos, and tan functions on this calculator use degrees, not radians. If you are working with a value in radians, multiply it by 180 / π before applying the function. For example, sin(π/6 radians) = sin(30°). Enter 30, then press sin to get 0.5.

Calculation tips

For complex expressions, work in stages — calculate inner expressions first, note the result, then use it in the outer expression. Remember the order of operations (PEMDAS/BODMAS): parentheses first, then exponents, then multiplication and division left-to-right, and finally addition and subtraction left-to-right.

Frequently asked questions

Why does the calculator show tiny rounding errors?

Digital computers represent decimal numbers in binary floating-point format, which cannot express all decimal fractions exactly. For example, 0.1 + 0.2 might show as 0.30000000000000004 instead of 0.3. This is a fundamental limitation of IEEE 754 floating-point arithmetic, not a bug in the calculator.

Is my calculation data private?

Yes. All calculations happen locally in your browser using JavaScript. No data is transmitted to any server, and your calculation history is stored only in your browser's memory for the current session.

Can I type a full expression like (4 + 5) * 3 at once?

Yes. Click the calculator display area (or the surrounding panel) to give it keyboard focus, then type the entire expression including parentheses. Press Enter or = to evaluate. The calculator validates that the expression contains only digits, spaces, the four basic operators, decimal points, and parentheses before evaluating, so complex nested expressions work correctly.

Why does 2 + 3 × 4 equal 14 and not 20?

Because multiplication has higher precedence than addition under standard mathematical rules (PEMDAS / BODMAS). The calculator evaluates 3 × 4 = 12 first, then adds 2, giving 14. If you want addition to happen first, wrap it in parentheses: (2 + 3) * 4 = 20.