# smithmetic
> we did the math.

smithmetic is a fast, free online calculator and converter site. built on cloudflare workers for sub-50ms responses globally. 108 calculators across 5 categories: convert, countdown, finance, health, math.

## calculators
- Acres to Square Meters Converter: https://smithmetic.com/convert/acres-to-sq-m
- Air Fryer Conversion Calculator: https://smithmetic.com/convert/air-fryer-conversion
- Amps to Watts Converter: https://smithmetic.com/convert/amps-to-watts
- Celsius to Fahrenheit Converter: https://smithmetic.com/convert/celsius-to-fahrenheit
- Celsius to Kelvin Converter: https://smithmetic.com/convert/celsius-to-kelvin
- Celsius to Rankine Converter: https://smithmetic.com/convert/celsius-to-rankine
- Centimeters to Feet & Inches Converter: https://smithmetic.com/convert/cm-to-feet
- Centimeters to Inches Converter: https://smithmetic.com/convert/cm-to-inches
- Centimeters to Millimeters Converter: https://smithmetic.com/convert/cm-to-mm
- Cups to Milliliters Converter: https://smithmetic.com/convert/cups-to-ml
- Days to Hours Converter: https://smithmetic.com/convert/days-to-hours
- Days to Weeks Converter: https://smithmetic.com/convert/days-to-weeks
- Fahrenheit to Celsius Converter: https://smithmetic.com/convert/fahrenheit-to-celsius
- Feet & Inches to Centimeters Converter: https://smithmetic.com/convert/feet-to-cm
- Feet per Second to MPH Converter: https://smithmetic.com/convert/fps-to-mph
- Feet to Inches Converter: https://smithmetic.com/convert/feet-to-inches
- Feet to Meters Converter: https://smithmetic.com/convert/feet-to-meters
- Fluid Ounces to Milliliters Converter: https://smithmetic.com/convert/fl-oz-to-ml
- GB to MB Converter: https://smithmetic.com/convert/gb-to-mb
- GB to TB Converter: https://smithmetic.com/convert/gb-to-tb
- Gallons to Liters Converter: https://smithmetic.com/convert/gallons-to-liters
- Grams to Ounces Converter: https://smithmetic.com/convert/grams-to-oz
- Hours to Days Converter: https://smithmetic.com/convert/hours-to-days
- Hours to Minutes Converter: https://smithmetic.com/convert/hours-to-minutes
- Inches to Centimeters Converter: https://smithmetic.com/convert/inches-to-cm
- Inches to Feet Converter: https://smithmetic.com/convert/inches-to-feet
- Inches to Millimeters Converter: https://smithmetic.com/convert/inches-to-mm
- KM/H to MPH Converter: https://smithmetic.com/convert/kmh-to-mph
- Kelvin to Celsius Converter: https://smithmetic.com/convert/kelvin-to-celsius
- Kilograms to Pounds Converter: https://smithmetic.com/convert/kg-to-lbs
- Kilograms to Stone Converter: https://smithmetic.com/convert/kg-to-stone
- Kilometers to Miles Converter: https://smithmetic.com/convert/km-to-miles
- Liters to Gallons Converter: https://smithmetic.com/convert/liters-to-gallons
- Liters to Pints Converter: https://smithmetic.com/convert/liters-to-pints
- MB to GB Converter: https://smithmetic.com/convert/mb-to-gb
- MPH to Feet per Second Converter: https://smithmetic.com/convert/mph-to-fps
- MPH to KM/H Converter: https://smithmetic.com/convert/mph-to-kmh
- Meters to Feet Converter: https://smithmetic.com/convert/meters-to-feet
- Meters to Yards Converter: https://smithmetic.com/convert/meters-to-yards
- Miles to Kilometers Converter: https://smithmetic.com/convert/miles-to-km
- Milliliters to Cups Converter: https://smithmetic.com/convert/ml-to-cups
- Milliliters to Fluid Ounces Converter: https://smithmetic.com/convert/ml-to-fl-oz
- Milliliters to Tablespoons Converter: https://smithmetic.com/convert/ml-to-tbsp
- Milliliters to Teaspoons Converter: https://smithmetic.com/convert/ml-to-tsp
- Millimeters to Centimeters Converter: https://smithmetic.com/convert/mm-to-cm
- Millimeters to Inches Converter: https://smithmetic.com/convert/mm-to-inches
- Minutes to Hours Converter: https://smithmetic.com/convert/minutes-to-hours
- Ounces to Grams Converter: https://smithmetic.com/convert/oz-to-grams
- Pints to Liters Converter: https://smithmetic.com/convert/pints-to-liters
- Pounds to Kilograms Converter: https://smithmetic.com/convert/lbs-to-kg
- Rankine to Celsius Converter: https://smithmetic.com/convert/rankine-to-celsius
- Square Feet to Square Meters Converter: https://smithmetic.com/convert/sq-ft-to-sq-m
- Square Meters to Acres Converter: https://smithmetic.com/convert/sq-m-to-acres
- Square Meters to Square Feet Converter: https://smithmetic.com/convert/sq-m-to-sq-ft
- Stone to Kilograms Converter: https://smithmetic.com/convert/stone-to-kg
- TB to GB Converter: https://smithmetic.com/convert/tb-to-gb
- Tablespoons to Milliliters Converter: https://smithmetic.com/convert/tbsp-to-ml
- Teaspoons to Milliliters Converter: https://smithmetic.com/convert/tsp-to-ml
- Watts to Amps Converter: https://smithmetic.com/convert/watts-to-amps
- Weeks to Days Converter: https://smithmetic.com/convert/weeks-to-days
- Yards to Meters Converter: https://smithmetic.com/convert/yards-to-meters
- Age in Days Calculator: https://smithmetic.com/countdown/age-in-days
- Date Difference Calculator: https://smithmetic.com/countdown/date-difference
- Days Until Calculator: https://smithmetic.com/countdown/days-until
- How Old Am I? Calculator: https://smithmetic.com/countdown/how-old-am-i
- Break-Even Calculator: https://smithmetic.com/finance/break-even-calculator
- Compound Interest Calculator: https://smithmetic.com/finance/compound-interest
- Discount Calculator: https://smithmetic.com/finance/discount-calculator
- Down Payment Calculator: https://smithmetic.com/finance/down-payment-calculator
- Effective Tax Rate Calculator: https://smithmetic.com/finance/tax-bracket-calculator
- Electricity Cost Calculator: https://smithmetic.com/finance/electricity-cost-calculator
- Freelance Rate Calculator: https://smithmetic.com/finance/hourly-rate-calculator
- Gas Cost Calculator: https://smithmetic.com/finance/gas-cost-calculator
- Hourly to Salary Calculator: https://smithmetic.com/finance/hourly-to-salary
- Inflation Calculator: https://smithmetic.com/finance/inflation-calculator
- Loan Payment Calculator: https://smithmetic.com/finance/loan-payment
- Markup Calculator: https://smithmetic.com/finance/markup-calculator
- Mortgage Calculator: https://smithmetic.com/finance/mortgage-calculator
- Pay Raise Calculator: https://smithmetic.com/finance/pay-raise-calculator
- Profit Margin Calculator: https://smithmetic.com/finance/margin-calculator
- ROI Calculator: https://smithmetic.com/finance/investment-return
- Rent vs. Salary Calculator: https://smithmetic.com/finance/rent-vs-salary
- Salary to Hourly Calculator: https://smithmetic.com/finance/salary-to-hourly
- Sales Tax Calculator: https://smithmetic.com/finance/sales-tax
- Savings Goal Calculator: https://smithmetic.com/finance/savings-goal-calculator
- Should I Buy It? Calculator: https://smithmetic.com/finance/should-i-buy-it
- Simple Interest Calculator: https://smithmetic.com/finance/simple-interest-calculator
- Split Bill Calculator: https://smithmetic.com/finance/split-bill-calculator
- Tip Calculator: https://smithmetic.com/finance/tip-calculator
- Unit Price Comparison Calculator: https://smithmetic.com/finance/unit-price-compare
- BMI Calculator: https://smithmetic.com/health/bmi-calculator
- Body Fat Percentage Calculator: https://smithmetic.com/health/body-fat-calculator
- Daily Calorie Calculator: https://smithmetic.com/health/calorie-calculator
- Daily Water Intake Calculator: https://smithmetic.com/health/water-intake-calculator
- Ideal Weight Calculator: https://smithmetic.com/health/ideal-weight-calculator
- Running Pace Calculator: https://smithmetic.com/health/pace-calculator
- Sleep Cycle Calculator: https://smithmetic.com/health/sleep-calculator
- Exponent Calculator: https://smithmetic.com/math/exponent-calculator
- Fraction to Decimal Calculator: https://smithmetic.com/math/fraction-to-decimal
- Logarithm Calculator: https://smithmetic.com/math/log-calculator
- Modulo Calculator: https://smithmetic.com/math/modulo-calculator
- Number Formatter: https://smithmetic.com/math/number-formatter
- Percentage Calculator: https://smithmetic.com/math/percentage-of
- Percentage Change Calculator: https://smithmetic.com/math/percentage-change
- Percentage Decrease Calculator: https://smithmetic.com/math/percentage-decrease
- Percentage Increase Calculator: https://smithmetic.com/math/percentage-increase
- Ratio Calculator: https://smithmetic.com/math/ratio-calculator
- Square Root Calculator: https://smithmetic.com/math/square-root

## how to use
visit any calculator page to use the interactive tool. each page includes the formula, step-by-step instructions, a worked example, frequently asked questions, and an in-depth written guide. precomputed answer pages also exist for common values, each with the worked arithmetic, a conversion table, and real-world context.
example: https://smithmetic.com/convert/celsius-to-fahrenheit/180 → "180°C = 356°F"

## accuracy & methodology
every calculator shows the formula it uses. conversions use exact internationally-defined constants (1 inch = 2.54 cm, 1 lb = 0.45359237 kg, 1 mile = 1.609344 km); finance and health tools use standard published formulas (loan amortization, compound interest, BMI, Mifflin-St Jeor for calories). full documentation of constants and sources:
https://smithmetic.com/methodology

## api for agents (mcp)
smithmetic exposes all 108 calculators to AI agents as a Model Context Protocol (MCP) server.
endpoint: https://smithmetic.com/mcp (stateless JSON-RPC 2.0 over Streamable HTTP; POST only)
tools: list_calculators (browse the catalog), describe_calculator (inputs + formula for one), calculate (run a conversion or calculation).
example: POST {"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"calculate","arguments":{"calculator":"celsius-to-fahrenheit","inputs":{"celsius":180}}}} → 356°F

## about
built and maintained by Eric Smith. https://smithmetic.com/about

## install as app
smithmetic is a progressive web app (PWA). install it on any device from the browser — no app store needed.
instructions: https://smithmetic.com/install

## sitemap
https://smithmetic.com/sitemap.xml

## contact
hello@smithmetic.com