These tools are for students checking a grade, travelers and remote teams working across time zones, cooks and DIYers converting measurements, and hobbyists sizing a resistor or a wire.
Each one uses a fixed formula or your browser's built-in time zone database, and the math runs on your device. The Currency Converter is the only one that goes online: it downloads a daily rate table, and the amounts you type are not sent anywhere.
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All converters
Unit Converter
Convert length, weight, temp, volume.
Currency Converter
Convert currencies with live rates.
Age Calculator
Find exact age in years, months, and days.
Percentage Calculator
Find a percentage, increase/decrease, or add/subtract %.
Grade Calculator
Final grade needed and weighted average grade.
Hours Calculator
Hours between two times, with decimal hours.
Timer & Stopwatch
Countdown timer with presets, plus a lap stopwatch.
Countdown to a Date
Count down to any future date and time.
Date Calculator
Count days between dates, or add and subtract days.
CM to Inches
Convert centimeters to inches.
KG to LBS
Convert kilograms to pounds.
MM to Inches
Convert millimeters to inches.
Celsius to Fahrenheit
Convert temperatures instantly.
Roman Numeral Converter
Convert numbers and dates to Roman numerals.
Fraction to Decimal Chart
Printable 1/64 chart and fraction converter.
Time Zone Converter
Convert times across zones and plan meetings.
PST to EST
Pacific to Eastern time, with an hourly chart.
CST to EST
Central to Eastern time, with an hourly chart.
UTC to EST
UTC to Eastern time, summer and winter.
GMT to EST
London or GMT to Eastern time, with BST.
UTC to PST
UTC to Pacific time, summer and winter.
EST to IST
US Eastern to India time, and back.
Binary to Decimal
Convert binary and decimal, with steps.
Hex to Decimal
Convert hex and decimal, with a 00-FF chart.
PST to CST
Pacific to Central time, with an hourly chart.
MST to EST
Mountain or Arizona to Eastern time.
CET to EST
Central European to Eastern time.
Voltage Drop Calculator
Voltage drop and wire size for copper or aluminum.
Ohm's Law Calculator
Solve volts, amps, ohms and watts.
Resistor Color Code
Decode 4, 5 and 6 band resistors.
LED Resistor Calculator
Find the right resistor for an LED.
Electricity Cost Calculator
kWh and cost per day, month and year.
Sig Fig Calculator
Count and round significant figures.
Business Days Calculator
Working days with US, CA, UK, AU holidays.
Calorie Calculator
Daily calories to lose or maintain.
Calorie Deficit Calculator
Daily target and weeks to goal.
CM to Feet and Inches
Convert centimeters to feet and inches.
Compound Interest Calculator
See how savings grow over time.
Duration Calculator
Add or subtract two time durations.
Feet to CM
Convert feet and inches to cm.
Fraction Calculator
Add, subtract, multiply, or divide fractions.
Gallons to Liters
Convert gallons, quarts, cups, liters.
Grams to Ounces
Convert grams to ounces.
Inches to MM
Convert inches to mm and cm.
KM to Miles
Convert kilometers to miles.
LBS to KG
Convert pounds to kilograms.
Macro Calculator
Daily protein, carbs and fat.
Oz to ML
Convert fluid ounces to milliliters.
Percent Change
Percent increase and decrease.
Hours Calculator
Hours worked and weekly timesheet.
Square Footage Calculator
Area in sq ft, sq m and acres.
MPH to KMH
Convert mph, km/h, knots and m/s.
Average Calculator
Mean, median, mode and range.
Quadratic Formula Calculator
Roots, discriminant and vertex.
Fahrenheit to Celsius
Convert F to C with a chart.
GPA Calculator
Semester and cumulative GPA.
Reseller Fee Calculators
Whatnot, Depop, Mercari and more.
Whatnot Fee Calculator
Tiered commission, payout and profit.
Depop Fee Calculator
US fees, boost and payout.
Grailed Fee Calculator
Commission tiers and processing.
Mercari Fee Calculator
10% fee, payout and profit.
Poshmark Fee Calculator
Flat fee and 20% commission.
TCGplayer Fee Calculator
Commission, cap and transaction fee.
KDP Royalty Calculator
Kindle and paperback royalties.
3D Print Cost Calculator
Cost per part and selling price.
Robux Tax Calculator
Roblox fee and price to list.
BAC Calculator
Estimate blood alcohol content.
Tablespoons to Cups
Convert tablespoons to cups.
TDEE Calculator
Total daily energy expenditure.
Tsp to Tbsp
Convert teaspoons to tablespoons.
Weeks in a Year
How many weeks in a year, and weeks left.
GCF & LCM Calculator
Find the GCF (GCD, HCF) and LCM of 2 to 10 numbers with steps.
Scientific Notation Calculator
Convert numbers and calculate in scientific notation.
One Rep Max Calculator
Estimate your 1RM from any set, with a percentage chart.
Standard Deviation Calculator
Sample and population standard deviation, variance and steps.
Probability Calculator
Two-event and binomial probability with steps.
Linear Regression Calculator
Line of best fit, r, R-squared and a scatter plot.
P-Value Calculator
P-value from z, t, chi-square or F with critical values.
Z-Score Calculator
Z-score, percentile and probability from a value or z.
Confidence Interval Calculator
Confidence interval for a mean or a proportion.
IBAN Validator
Check an IBAN with the mod-97 test.
Phone Number Parser
Validate and format phone numbers for any country.
How to choose
This hub mixes several kinds of calculator. Find the question you're asking, then pick the tool built for it.
How much is this in another unit?
The Unit Converter covers length, weight, volume and temperature. The single-purpose pages, CM to Inches, MM to Inches, KG to LBS and Celsius to Fahrenheit, add printable charts for the conversions people look up most. For tape-measure fractions, use the Fraction to Decimal Chart. Money is different, because rates move: treat the Currency Converter's daily mid-market rate as an estimate, not a quote.
What time is it there?
The Time Zone Converter compares several zones at once, applies daylight saving time for the exact date and finds shared working hours. For one common pair, the dedicated pages such as PST to EST, UTC to EST and EST to IST add a 24-hour chart you can print.
How long, or when?
The Date Calculator counts days between dates or adds days to one. The Business Days Calculator skips weekends and US, Canadian, UK or Australian holidays. The Age Calculator gives exact age in completed years, months and days. The Time Duration Calculator handles hours between clock times, including overnight shifts. For a live clock, use the Countdown to a Date or Timer & Stopwatch.
What's the number?
The Percentage Calculator covers percent-of, percent change and adding a percentage. The Grade Calculator handles weighted courses and the score you need on a final. For number systems, there are Binary to Decimal, Hex to Decimal and the Roman Numeral Converter.
Electrical work
Use Ohm's Law when you know two of voltage, current, resistance and power. The LED Resistor and Resistor Color Code calculators cover small circuits, the Voltage Drop Calculator covers wire runs, and the Electricity Cost Calculator turns watts into kWh and cost.
Getting results you can trust
Most "wrong" conversions come from mixing up unit variants. The US and UK gallon are different sizes, and a US short ton isn't a metric tonne. Rounding too early in a multi-step calculation causes errors too. Check which variant you mean, keep full precision until the last step, and treat currency results as same-day estimates, not quotes. Why unit converters disagree and percentage vs. percentage points cover the most common traps.
Guides
How to Calculate Percentage: Formulas and Worked Examples
The three core percentage formulas, percent change and reverse percentages.
GUIDEPercentage Increase vs. Percentage Points
Why 5% to 10% is both a 100% increase and 5 percentage points.
GUIDEHow to Calculate Your Final Grade (Weighted and Points-Based)
Weighted and points-based grades, and the score you need on the final.
GUIDEEST vs EDT and PST vs PDT: Which Applies Right Now?
Standard vs daylight time on both coasts and which one applies now.
GUIDEUTC vs GMT: What's the Difference?
Atomic time vs solar time, leap seconds and what the Z in a timestamp means.
GUIDEHow to Convert Binary to Decimal and Decimal to Binary
Step-by-step methods in both directions, plus the hex shortcut.
GUIDEHow Currency Conversion Actually Works (And Why Rates Are Never Truly Live)
Why converter rates update regularly but are never truly live.
GUIDEWhy Age Calculators Give Different Answers
Why two age calculators can give different answers for one birth date.
Frequently asked questions
Rates are pulled from a public exchange-rate API roughly once a day โ suitable for general reference, not real-time trading decisions.
Yes โ length, weight, and volume conversions use standard SI-based conversion factors; temperature conversions correctly handle Celsius, Fahrenheit, and Kelvin's different zero points.
Yes. They read the offset from the IANA time zone database built into your browser for the exact date you pick, so labels such as EST and EDT, or GMT and BST, switch on the correct dates.
No. Every calculation runs in your browser. The Currency Converter is the only tool that connects to the internet, and it only downloads a daily table of exchange rates. The amounts you type stay on your device.
Yes. The Business Days Calculator skips weekends and can also skip US, Canadian, UK or Australian public holidays when counting between dates or adding working days.