Everyday numbers, sorted in seconds.
JustCalcs is a set of small, focused calculators for the questions that come up at home, at work and on the road. Every page shows the formula and a worked example, so you can check the answer instead of trusting it.
Everything runs in your browser. No account, no upload, no stored data.
Example results
What a calculation looks like
- 10 cm in inches
- 3.937 in
- 10 km in 55:00
- 5:30 /km
- 20% off 49.90
- 39.92
1 inch = 2.54 cm, exactly
running pace per kilometre
you save 9.98
Everything in one place
Calculator sections
Pick the section that matches the task. Each calculator has a page of its own with the method, the limits of the result and links to the neighbouring tools.
Auto, Road Trips & Travel
car calculators
- Distance Between Cities
- EV Charging Calculator
- Fuel Cost Calculator
- Gas Mileage Calculator
- Speed, Distance and Time Calculator
- Tire Size Calculator
- Travel Currency Calculator
- Travel Time Calculator
- Trip Budget Calculator
Dates & Time
date calculators
- Age Calculator
- Business Days Calculator
- Date Calculator
- Days Between Dates Calculator
- Days Until Calculator
- Expiration Date Calculator
- Time Duration Calculator
- Time Zone Converter
- Work Hours Calculator
Everyday Money
personal finance calculators
- Budget Calculator
- Discount Calculator
- Emergency Fund Calculator
- Inflation Calculator
- Margin and Markup Calculator
- Net Worth Calculator
- ROI Calculator
- Sales Tax Calculator
- Savings Goal Calculator
- Simple Interest Calculator
- Split Bill Calculator
- Tip Calculator
- Unit Price Calculator
Food & Cooking
cooking calculators
- Cake Pan Converter
- Coffee Ratio Calculator
- Cooking Time Calculator
- Dough Hydration Calculator
- Grams to Cups Calculator
- Recipe Cost Calculator
- Recipe Nutrition Calculator
- Recipe Scaling Calculator
- Serving Size Calculator
Home, DIY & Utilities
home improvement calculators
- Air Conditioner BTU Calculator
- Appliance Energy Calculator
- Brick Calculator
- Concrete Block Calculator
- Concrete Calculator
- Drywall Calculator
- Electricity Cost Calculator
- Fence Calculator
- Floor Screed Calculator
- Flooring Calculator
- Gravel Calculator
- Grout Calculator
- Home Renovation Cost Calculator
- Mulch and Soil Calculator
- Paint Calculator
- Plaster Calculator
- Pool Volume Calculator
- Roofing Calculator
- Square Footage Calculator
- Tile Calculator
- Utility Cost Calculator
- Wallpaper Calculator
Loans, Savings and Investments
loan calculators
- 401(k) Calculator 2026
- Amortization Calculator
- APR to APY Calculator
- Auto Loan Calculator
- CD and Deposit Calculator
- Compound Interest Calculator
- Credit Card Payoff Calculator
- Debt Snowball Calculator
- Debt-to-Income Calculator
- Down Payment Calculator
- Home Affordability Calculator
- Investment Growth Calculator
- Loan Calculator
- Loan Payoff Calculator
- Mortgage Calculator
- Refinance Calculator
- Rent Affordability Calculator
- Rent vs. Buy Calculator
- Retirement Savings Calculator
- RMD Calculator 2026
- Roth IRA Contribution Calculator 2026
- Traditional IRA Calculator 2026
Percentages & Everyday Math
math calculators
- Aspect Ratio Calculator
- Average Calculator
- Circle Area Calculator
- Cylinder Volume Calculator
- Fraction Calculator
- GPA Calculator
- Grade Calculator
- Ohm's Law Calculator
- Online Calculator
- Percentage Calculator
- Percentage Change Calculator
- Pythagorean Theorem Calculator
- Quadratic Formula Calculator
- Random Number Generator
- Ratio and Proportion Calculator
- Rounding Calculator
- Scientific Calculator
- Square Root Calculator
- Standard Deviation Calculator
- Triangle Area Calculator
Pet and Aquarium Calculators
pet calculators
- Aquarium Substrate Calculator
- Aquarium Volume Calculator
- Cat Age Calculator
- Cat Food Calculator
- Dog Age Calculator
- Dog Food Calculator
Pregnancy and Family Calculators
pregnancy calculators
- Age Difference Calculator
- Conception Date Calculator
- Menstrual Cycle Calculator
- Ovulation Calculator
- Pregnancy Due Date Calculator
- Pregnancy Week Calculator
- Pregnancy Weight Gain Calculator
- Relationship Duration Calculator
- Wedding Budget Calculator
Unit Converters
unit converter
- Area Converter
- Clothing Size Converter
- Cooking Volume Converter
- Currency Converter
- Data Storage Converter
- Download Time Calculator
- Energy Converter
- Fuel Economy Converter
- Length Converter
- Power Converter
- Pressure Converter
- Scale Calculator
- Shoe Size Converter
- Speed Converter
- Temperature Converter
- Time Unit Converter
- Volume Converter
- Weight Converter
Weight, Body & Fitness
weight calculators
- BMI Calculator
- BMR Calculator
- Body Fat Calculator
- Calorie Deficit Calculator
- Calorie Needs Calculator
- Calories Burned Calculator
- Ideal Weight Range Calculator
- Lean Body Mass Calculator
- Macro Calculator
- Pace Calculator
- Protein Intake Calculator
- Sleep Calculator
- Waist-to-Height Ratio Calculator
- Waist-to-Hip Ratio Calculator
- Water Intake Calculator
- Weight Gain Timeline Calculator
- Weight Loss Timeline Calculator
Work, Pay and Tax Calculators
paycheck calculators
- Child Support Payment Calculator
- Commission Calculator
- Federal Income Tax Calculator 2026
- Federal Paycheck Estimate 2026
- Federal Tax Refund Estimate 2026
- Hourly to Salary Calculator
- PTO Accrual Calculator
- Self-Employment Tax Calculator 2026
- Social Security PIA Calculator 2026
- US Federal Overtime Calculator
How it works
Three steps, no learning curve
The calculators are built to be read as much as used: the numbers you enter stay visible, and so does the arithmetic that turns them into a result.
01 · Enter what you know
Fields start with a sensible example so you can see the shape of the calculation before replacing the values with your own.
02 · Read the whole answer
Along with the result you get the formula, the units used and the intermediate values, rounded only at the point of display.
03 · Share the exact result
The inputs live in the address bar, so copying the link sends someone the calculation itself, not a screenshot of it.
Why these calculators
Small tools that stay out of the way
One task per page
No dashboard to configure and no unrelated fields competing for attention.
Exact conversion factors
Unit ratios are kept exact in the calculation; rounding happens only in the output.
Works on a phone
Full-width inputs, native pickers and no horizontal scrolling on a narrow screen.
Free and open
No sign-up wall, no trial period and no lead form between you and the answer.
Ready when you are
Find the calculator you need.
The catalogue lists every calculator on the site, grouped by the kind of question it answers.