Math Expression Evaluator

Evaluate complex math expressions instantly with variables, functions, unit conversions, and base conversions. Custom recursive descent parser with precision mode. 100% local.

Was this tool helpful?

How to Use

The Math Expression Evaluator parses and evaluates mathematical expressions in real time using a custom recursive descent parser. It supports arithmetic, functions, variables, unit conversions, and multiple number bases, all running locally in your browser with zero external dependencies.

How to use this tool

Type an expression in the input field. Results update live as you type, so you can see the answer before pressing Enter. The parser handles standard arithmetic, parentheses, and operator precedence automatically.
Press Enter to commit the expression to your history. The history panel stores your last 50 calculations and lets you click any entry to recall it. Press Arrow Up to quickly recall the most recent expression.
Define variables by typing assignments like x = 42 or rate = 0.05. Variables persist for your entire session and appear in the Variables panel. Use them in later expressions: x * rate, sqrt(x).
Use built-in functions like sin(PI/4), sqrt(144), log(1000), max(5, 3, 8), or round(3.14159, 2). The Quick Reference panel lists all available functions, constants, and units.
Convert units by typing expressions like 5km to miles, 100F to C, or 2.5lb to kg. Temperature conversions use the correct mathematical formulas, not simple multiplication factors.
Enable Precision mode to avoid IEEE 754 floating point errors. In precision mode, 0.1 + 0.2 returns exactly 0.3 instead of 0.30000000000000004.

Number base support

Enter numbers in hexadecimal (0xFF), binary (0b1010), or octal (0o77) notation. The evaluator converts them to decimal automatically. Combine with bitwise operators for low-level calculations: 0xFF & 0b11110000 returns 240.

About This Tool

How the Parser Works

This evaluator uses a recursive descent parser, a top-down parsing technique where each grammar rule maps to a function. The parser implements correct operator precedence through a hierarchy of parsing functions: bitwise operations at the lowest precedence, then addition and subtraction, multiplication and division, exponentiation (right-associative), unary operators, implicit multiplication, and finally primary expressions like numbers, variables, and function calls. This architecture handles complex nested expressions like 2^3^2 (which equals 512, not 64) and 2(3+4) (implicit multiplication) correctly.

Why Floating Point Errors Happen

Computers represent decimal numbers using IEEE 754 binary floating point, which cannot exactly represent many common decimals. The number 0.1, for example, has an infinite repeating representation in binary (0.0001100110011...), similar to how 1/3 has an infinite representation in decimal (0.3333...). When two of these imprecise representations are added, the rounding errors compound. The precision mode in this evaluator sidesteps this problem by scaling operands to integers before performing arithmetic. For 0.1 + 0.2, it computes (1 + 2) / 10 = 0.3 exactly. This technique works reliably for addition, subtraction, and multiplication of decimal numbers.

Comparison with Other Calculators

Unlike browser console evaluation (eval()), this tool uses a safe custom parser that never executes arbitrary JavaScript. Unlike heavy math libraries like math.js (170KB+), the entire parser ships under 5KB with no external dependencies. It covers the practical needs of developers, students, and engineers, including unit conversions that Google Calculator and Wolfram Alpha handle, but runs 100% offline in your browser.

Why Use This Tool

When You Need a Smarter Calculator

The built-in calculator on your OS handles simple arithmetic, but falls short when you need variables, functions, or unit conversions. Opening a terminal and typing python3 -c "..." works but is slow and context-switching. Browser DevTools console.log() evaluates JavaScript but not math notation like 2^10 (which is XOR in JS, not exponentiation). This tool fills that gap: a dedicated math workspace that understands mathematical notation, persists variables across expressions, and converts units inline.

Developers use it to verify bitwise mask calculations (0xFF & 0b11001100), quickly convert between measurement systems while reading specifications (4.7in to cm), and check trigonometric values (sin(PI/6)). Students use it to verify homework calculations step by step, defining variables and building up complex expressions. Engineers use the precision mode when decimal accuracy matters in financial or scientific calculations.

Privacy and Offline Use

Every calculation runs in your browser. The expression parser is pure JavaScript with no network calls, no telemetry, and no server-side processing. Your expressions and variables never leave your device. The tool works offline after the initial page load, making it suitable for air-gapped environments and sensitive calculations.

FAQ

What math operations does this evaluator support?

Arithmetic (+, -, *, /, %, ^), unary negation, bitwise operations (&, |, ~, <<, >>), parentheses for grouping, implicit multiplication (2PI, 3(4+5)), and right-associative exponentiation. The parser handles operator precedence automatically: exponents before multiplication/division, which come before addition/subtraction.

How does the precision mode avoid floating point errors?

Precision mode uses integer arithmetic internally by scaling decimal numbers to integers before performing operations, then scaling back. For example, 0.1 + 0.2 normally returns 0.30000000000000004 due to IEEE 754 limitations. Precision mode computes (1 + 2) / 10 = 0.3 exactly. Results display up to 15 significant digits.

Can I define and reuse variables across expressions?

Yes. Type an assignment like x = 5 and press Enter. The variable x is then available in subsequent expressions such as x^2 + 3x or sqrt(x). Variables persist for your entire session. You cannot reassign built-in constants like PI or E.

What unit conversions are supported?

Length (km/miles, m/ft, cm/in, mm/in, yd/m), weight (kg/lb, g/oz), volume (l/gal, ml/floz), temperature (F/C/K), and speed (mph/kph). Use the syntax '5km to miles' or '100F to C'. Temperature conversions use the correct formulas, not simple multiplication.

Is my data sent to a server?

No. The expression parser is a custom recursive descent parser built entirely in JavaScript. All evaluation happens locally in your browser. No expressions, variables, or results are transmitted to any server. The tool works fully offline once the page loads.