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Calculator Online Tools

60 tools

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Percent Calculator

Calculate percentages easily

Unit Price Calculator

Calculate unit prices to find the best deal instantly

Dog & Cat Age Calculator

Convert dog (small to giant) and cat years to human years. Compare MOE, AKC & UCSD methods, with chart and life stages

Japanese Era / Western Year Converter

Convert Japanese Era to Western year and vice versa with age, zodiac & more

BMI Calculator

Calculate BMI with ideal weight comparison, body fat estimation & trend graph

Age Calculator

Calculate age, zodiac, milestone years, and more from your birthday

Electricity Cost Calculator

Calculate electricity costs for appliances with multi-device totals and replacement savings

Date Calculator

Calculate date ranges, business days & add/subtract dates with JP holiday support

Weeks Calculator

Weeks and days between two dates, the date N weeks from today, and this week's number

Days From Date Calculator

The date N days after or before today or any date, with the day of the week

Time Period Converter

Weeks in a month, days to years and more: convert days, weeks, months, years and hours at once

Anniversary Calculator

Days and months since any date, with milestone anniversaries (100, 1000 days), countdowns, card images and calendar export

Time Calculator

Add and subtract hours and minutes, work hours and time differences, even from a pasted list

Countdown Timer

Real-time countdown showing days, hours, minutes & seconds until your target date

Day of Week Calculator

Instantly find the day of the week for any date with calendar and zodiac info

Calorie & PFC Balance Calculator

Calculate BMR, TDEE & PFC balance with 4 formulas comparison and 7 presets

Unit Converter

Convert length, weight, area, volume, temperature, speed & data

Due Date Calculator

Calculate due date, pregnancy week & trimester from LMP

Bill Splitter

Split a bill evenly or with adjustments, with rounding options

Roman Numeral Converter

Convert between Arabic and Roman numerals with breakdown

Discount Calculator

Calculate sale prices from discount rate or amount, plus reverse

Sleep Calculator

Find ideal bed/wake times based on 90-minute sleep cycles

Scientific Calculator

Scientific calculator with trig, log, power & memory functions

Salary Converter

Convert hourly, daily, monthly & annual salary instantly

Ovulation Calculator

Predict ovulation, fertile window & next period from your cycle

Fuel Cost Calculator

Calculate fuel cost from distance, mileage & price

Speed Distance Time Calculator

Solve for speed, distance or time with unit conversion

Tsubo Area Converter

Convert tsubo, square meters, tatami & square feet

GPS Coordinate Converter

Convert GPS coordinates between DMS and decimal degrees

Percentage Change Calculator

Calculate percentage increase/decrease between two values

Deviation Score Calculator

Calculate deviation score (hensachi) from score, mean & SD

Car Tax Calculator

Estimate annual Japanese car tax from engine size & year

Tip Calculator

Calculate tip, total, and split per person

Ratio Calculator

Simplify ratios and solve A:B = C:?

GCD & LCM Calculator

Find the GCD and LCM of multiple integers

Prime Checker & Factorization

Check if a number is prime and show its factorization

Descriptive Statistics Calculator

Compute mean, median, mode, variance, and SD

Area Calculator

Calculate area of triangle, rectangle, circle, trapezoid, etc.

BMR & TDEE Calculator

Calculate your BMR and TDEE

Rounding Calculator

Round, round up, or round down numbers

Business Day Calculator

Count business days and find the date N business days later

Running Pace Calculator

Calculate running pace, time, and distance

Step to Distance Calculator

Convert steps to distance and calories burned

Fraction Calculator

Add, subtract, multiply, divide, and simplify fractions

Quadratic Equation Solver

Solve ax^2 + bx + c = 0 with steps

Temperature Converter

Convert between Celsius, Fahrenheit, and Kelvin

Week Number Calculator

Find the ISO week number and week of month for a date

Ideal Weight Calculator

Calculate standard, beauty, and model weight from height

Cash Denomination Calculator

Break an amount into bills and coins

GPA Calculator

Calculate GPA from grades and credits

Simple Interest Calculator

Calculate simple interest from principal, rate, and term

Cooking Measurement Converter

Convert tablespoons, teaspoons, cc, cups, and grams

Water Intake Calculator

Estimate daily water intake from body weight

Heart Rate Zone Calculator

Calculate max heart rate and training zones

Shoe Size Converter

Convert shoe sizes between JP, US, UK, and EU

Permutation & Combination Calculator

Calculate permutations nPr, combinations nCr, and factorials

Body Fat Calculator

Estimate body fat percentage from measurements

One Rep Max Calculator

Estimate your one-rep max from weight and reps

Volume Calculator

Calculate volume of cube, cylinder, sphere, etc.

Pythagorean Theorem Calculator

Calculate sides of a right triangle

Related Guides

How Many Weeks Are in a Month? Days, Weeks, Months and Years Conversion Chart A month is about 4.35 weeks (4 weeks and 2–3 days). See the math, weeks per month and per year, 1,000 days in years and months, plus easy conversion charts. Dog & Cat Years to Human Years: Why ×7 Is Wrong (Charts by Size) Convert dog and cat years to human years with the AKC dog age chart by size, the FelineVMA cat age chart and the UCSD DNA formula, and see why ×7 is wrong. Unit Conversion Basics: Length, Weight, Temperature & Area Made Simple A clear guide to converting length (m/inch/ft), weight (kg/lb/oz), temperature (Celsius/Fahrenheit), and area (m²/tsubo/tatami). Learn the key reference numbers, the Fahrenheit-Celsius formula, and where conversions come up daily. Percentage Basics: How to Find X% Of, What Percent, Change, and Discounts Learn percentage math with formulas and examples: how to find X% of a number, what percent of the whole, rate of change, and discounts and tax, plus the most common mistakes. Electricity Cost & Savings: kWh, Unit Price, Appliance Wattage & Standby Power A clear guide to calculating electricity costs (kWh × rate + basic charge): typical wattage by appliance like air conditioners and fridges, standby power, reviewing your contracted amperage and rate plan, and saving tips you can start today. Calorie and PFC Basics: Basal Metabolism, TDEE, and Target Ratios A clear guide to basal metabolism and TDEE behind calorie counting, the roles and target ratios of PFC (protein, fat, carbohydrate), and how plans differ for fat loss and muscle gain. Not medical advice. Date & Day Calculations: Elapsed Days, Business Days, Days From Now A clear guide to counting days between two dates, business days (excluding holidays), a date N days before or after, and weeks. Learn leap-year and endpoint cautions, plus uses for deadline management and anniversaries. How to Calculate Japan Consumption Tax: Inclusive vs. Exclusive & Rounding Learn how to calculate Japan consumption tax with formulas and examples: converting pre-tax and tax-included prices, the 10% and reduced 8% rates, inclusive vs. exclusive pricing, rounding under one yen, and invoices. Due Date Calculation and Counting Pregnancy Weeks (Naegele Rule) A clear guide to calculating the due date with Naegele's rule and counting pregnancy weeks, months, and trimesters from the last period, plus why the due date is only an estimate. Not medical advice. 90-Minute Sleep Cycles: When to Sleep and Wake Up Refreshed Sleep runs in roughly 90-minute cycles. Learn how REM and non-REM work, how to back-calculate bedtime and wake time, how much sleep you need, and habits to improve quality. Not medical advice. Sale and Discount Math: X% Off, Stacked Discounts, and Effective Rate Learn how to find the sale price for X% off, reverse the discount rate, the pitfall of stacked discounts, how tax and point rewards interact, and the effective discount rate, with examples. What Is a Standard Score (Hensachi)? The Formula and What 60 or 70 Means Learn what the Japanese standard score (hensachi) is from the ground up: how it expresses your distance from the mean divided by the standard deviation around a base of 50, the formula, what a score of 60 or 70 means as a top percentile under a normal distribution, why it lets you compare different tests, and its limits. How to Calculate Fuel Cost: Formula From Distance, Real-World MPG, and Saving Tips Learn what fuel economy (km/L) means and how to calculate fuel usage and cost from your driving distance. We cover why real-world economy differs from the catalog figure, tips to cut fuel costs, and how to compare costs with hybrids and EVs. Mean vs. Median vs. Mode: Choosing the Right Measure of Center A clear guide to the difference between the mean, median, and mode. Learn why the arithmetic mean is vulnerable to outliers, when the median works best for skewed data like income or land prices, where the mode is useful, and how to pick a measure of center by the shape of the distribution. What Is Standard Deviation? Variance, Calculation, the Normal Distribution Learn what standard deviation is from the ground up: its meaning as a measure of spread, its relationship to variance (the square root), the step-by-step calculation, what large vs small values mean, the 68-95-99.7 rule of the normal distribution, and how it links to standard scores. How to Calculate Area: Triangle, Rectangle, Trapezoid, Circle Formulas & Units A friendly guide to finding area by shape: triangle (base x height / 2), rectangle and square, parallelogram, trapezoid, circle (radius x radius x pi), and rhombus, with worked examples. Plus how units like square meters, tsubo, and tatami relate. What Are BMR and TDEE? Mifflin-St Jeor Formula and Activity Factors Explained Learn the difference between basal metabolic rate (BMR) and total daily energy expenditure (TDEE), and how to calculate them: the Mifflin-St Jeor formula, activity factors from 1.2 to 1.9, targets for cutting and bulking, and individual variation as a caveat. Rounding Basics: Round Half Up, Round Up, Round Down, and How to Choose A beginner-friendly guide to rounding: the difference between round half up, round up, and round down, how banker's rounding (round half to even) works, rounding sales tax, Excel's ROUND, ROUNDUP, and ROUNDDOWN, which digit to round at, and practical usage. How to Count Business Days: Weekends, Holidays, and N Days Later Learn what a business day is from the ground up: working days excluding weekends and holidays, how to correctly count N business days later or earlier, the difference from calendar days, how to handle holidays and year-end breaks, and practical counting for deadlines and payment dates. Running Pace Basics: Pace, Time, Distance, and Target Pace Conversion Learn what running pace (min/km) means from the ground up: the relationship between pace, time, and distance, target times for 5K, 10K, half, and full marathon with per-kilometer conversions, and pace guidance for beginners, with formulas and charts. Steps, Distance, and Calories: Stride Length, and How Far and How Many Calories 10,000 Steps Are Learn how to turn steps into distance and calories from the basics: stride-length guidelines based on height, the formula to convert steps to distance, how to estimate calories burned from body weight and distance, and roughly how far and how many calories 10,000 steps are. Fraction Basics: Simplifying, Common Denominators, and the Four Operations Learn fraction basics from scratch: how to simplify and find common denominators, addition and subtraction (common denominators), multiplication and division (reciprocals), converting mixed and improper fractions, fraction-decimal conversion, and tips for reducing answers to lowest terms. How to Solve Quadratic Equations: Formula, Discriminant, Factoring & Completing the Square Learn how to solve quadratic equations from the basics: the general form ax^2+bx+c=0, the quadratic formula, using the discriminant D=b^2-4ac to count real roots, solving by factoring, completing the square, and the link to the parabola graph. Celsius vs Fahrenheit vs Kelvin: Temperature Conversion Made Simple Understand the temperature units Celsius (C), Fahrenheit (F), and Kelvin (K) from the ground up: how they differ, the Celsius-Fahrenheit conversion formulas, Kelvin and absolute zero, the freezing and boiling points of water, how to read overseas weather forecasts, and easy tricks to convert in your head. Standard, Beauty, and Model Weight Explained: How to Calculate Them with BMI Understand the difference between standard, beauty, and model weight and how to calculate them. Covers the standard weight formula from BMI 22 (height in m squared times 22), beauty weight (BMI 20) and model weight (around BMI 18) targets, how they differ from a healthy weight range, and a sensible approach to weight management. What Is an ISO Week Number? How to Count Weeks Under ISO 8601 A beginner-friendly guide to ISO 8601 week numbers: the rule that weeks start on Monday and the week containing the first Thursday is week 1, how to find the nth week, how it differs from "the nth week of the month," and how to use it in work calendars and project management. What Is Denomination Calculation? Counting Bills and Coins by Fewest Pieces Learn what denomination calculation is from the ground up: how to work out how many of each bill and coin you need for cash payroll or currency exchange, the fewest-pieces idea, preparing change, and use in registers and accounting. What Is GPA? Calculation, the 4.0 Scale, and Japan vs. Overseas Learn what GPA is from the ground up: the meaning of Grade Point Average, how grades like A/B/C are converted to points and averaged by credit weight, the 4.0 scale, differences between Japan and overseas, how it is used for study abroad and job hunting, and how to raise it. Cooking Measurement Basics: Tablespoons, Teaspoons, Cups, and Grams A beginner-friendly guide to cooking measurement basics: tablespoon (15ml), teaspoon (5ml), cup (200ml), cc vs ml, why volume (ml) and weight (g) do not match, substitutes when you have no measuring spoon, and gram conversions for common seasonings. How Much Water Do You Need a Day? Weight-Based Targets and Tips Learn how to estimate your daily water needs from body weight. Covers the weight x 30-35 ml guideline, water from food, how exercise and heat change the amount, the risks of overdrinking, and tips for steady hydration. General health information. What Are Heart Rate Zones? Max HR, the Karvonen Method, and Fat-Burning A beginner-friendly guide to heart rate zones: estimating max heart rate (220 minus age), the Karvonen method using resting heart rate, the fat-burning and aerobic zone ranges, how to gauge exercise intensity, and how to measure resting heart rate. This article is general information, not medical advice. International Shoe Size Differences Explained: JP, US, UK, EU Conversion International shoe sizes use different scales in every country. Learn how JP (cm), US, UK, and EU sizes relate, how men's/women's/kids sizes differ, why brands vary, how to choose when buying abroad, and how to measure your foot length correctly. Permutations vs Combinations: nPr and nCr Formulas, Factorials, and Examples Learn the difference between permutations and combinations from the ground up: the order-sensitive nPr and order-free nCr formulas, what factorials mean, worked examples like lotteries and team splits, repetition cases, and the link to Pascal's triangle. What Is Body Fat Percentage? How to Measure It, Targets by Sex and Age Learn what body fat percentage is from the ground up: how it differs from BMI, estimation methods such as bioelectrical impedance (Tanita-style) and the Navy circumference method, targets by sex and age, how home body composition scales work and their margins of error, and a healthy range. What Is 1RM (One-Rep Max)? Formulas, %1RM Chart, and Goal-Based Loading Learn what 1RM (one-rep max) is from the ground up: estimation formulas such as Epley and Brzycki, a %1RM chart showing the relationship between reps and weight, goal-based loading for strength, hypertrophy, and endurance, and how to measure it safely. What Is a Factorial (n!)? Why 0!=1, Permutations, and Explosive Growth Learn what a factorial (n!) is from the ground up: the product from 1 to n, why 0!=1, how the value grows explosively, its relationship to permutations and combinations, uses in probability and counting, and the overflow pitfalls in calculators. BMI vs Body Fat Percentage: The Difference, How to Calculate, and Why Both Matter Learn the difference between BMI and body fat percentage from the basics. BMI comes from height and weight, while body fat percentage is the share of fat in your body. See why a muscular person can have a high BMI but low body fat, the typical ranges, the limits of each, and why you should look at both. How to Find Volume: Cube, Cylinder, Cone, Sphere Formulas and Units Learn how to find volume from the basics: formulas for cubes, rectangular prisms, cylinders, cones, spheres, and triangular prisms, the "base area × height" idea, the relationship between cm³, m³, and liters, volume vs. capacity, and worked examples. What Is the Pythagorean Theorem? Meaning of a²+b²=c², Finding the Hypotenuse, and Famous Triples Learn what the Pythagorean theorem is from the ground up: the relationship a²+b²=c² describes in a right triangle, how to find the hypotenuse, famous integer ratios like 3:4:5, real-world uses such as distance between two points, and the idea behind the proof. What Is Pi (π)? Its Meaning (Circumference ÷ Diameter), Why ~3.14, and How to Use It Learn what pi (π) is from the ground up: that it equals circumference divided by diameter, its value of about 3.14, how it is used for circumference, circle area, and sphere volume, approximations and precision, its history, and tips for everyday calculation. BMI and Ideal Body Weight Explained: Formula, Ranges, and Limits A clear guide to the BMI formula and judgment ranges, ideal vs. beauty weight, the limits of BMI such as ignoring muscle, and how to use it for health management. Not medical advice. Wareki to Seireki: Conversion Basics & Era Chart (Reiwa, Heisei, Showa) How to convert between Japanese era years and the Western calendar, with mental-math tips and a Reiwa/Heisei/Showa chart. Learn what Western year Reiwa starts from, era-change cautions, document use, and age calculation.