Free Online Tools for Everything You Do
Browse 2,706+ free interactive tools - home improvement estimators, pet calculators, cooking converters, automotive tools, finance planners, fitness calculators, developer utilities and more. No sign-up. 100% private. Runs entirely in your browser.
Jsonpath Tester
Julian Date Converter — JDN, Julian Calendar & Ordinal Date (Free Online)
Free Julian date converter: Julian Day Number (astronomy), Julian calendar ↔ Gregorian, and ordinal dates (yyddd, yyyyddd, JDE Cyyddd) — plus MJD and heliocentric JD. Verified math, 100% client-side.
Jumbo Loan Calculator — Classification, Payment & Comparator (FHFA 2026 Limits)
Free jumbo loan calculator: check jumbo vs conforming classification against FHFA 2026 limits ($832,750 baseline, $1,249,125 high-cost), compute monthly payments, compare jumbo vs conforming costs, and check the DTI ratio. 100% in-browser.
Jwt Decoder
Decode JSON Web Tokens instantly.
Mock JWT Generator
Interactive Mock JWT Generator, Test JWT Token Creator, and Dummy JWT Signer with 100% SEMrush keyword optimization.
JWT Token Node.js – jsonwebtoken Implementation & Inspector
JWT token node js, json web token, json web token example, jwt token structure, jwt js, jwt javascript, json web token java, inspect json web token online, view jwt payload and header.
JWT – Secret Key Generator, Token Decoder & SHA-256 Hasher
Decode hex, what is sha256, access token decode, jwt secret key generator, sha256 hasher, jwt secret generator, sha1 hash decrypter, sha 256 decrypt, algorithm sha 256, jwt在线解密, decrypting sha256, sha1 hash decoder, how does sha 256 work, decrypt sha1, json extractor, sha256 encrypt, sha256 encoder, sha256 calc, is sha256 secure, sha hashing algorithm, sha256 code, decode rsa, oauth token decode, sha256 hash decoder, sha 256 hash decoder, python decode jwt, json web token node, go url encode, how jwt token works, sha256 hash decrypt.
Karvonen Formula Calculator — Target Heart Rate by Heart Rate Reserve
Free Karvonen formula calculator: target heart rate = ((HRmax − HRrest) × intensity%) + HRrest. Choose 220−age, Tanaka (208−0.7×age), or measured max HR. Full 5-zone table, worked steps, and FAQ. 100% client-side.
Katha to Square Feet Converter - Regional Katha Calculator
Free katha to square feet converter with verified regional values: Bihar 1361 sq ft, West Bengal 720 sq ft, Assam 2880 sq ft, Bangladesh 720 sq ft. Convert katha to sq ft, sq m, acres, hectares, bigha.
Kaya Identity Calculator — Decompose CO2 Emissions into 4 Drivers
Free Kaya identity calculator: decompose CO2 emissions into population, GDP per capita, energy intensity and carbon intensity. Solve for a missing factor or compare two scenarios. 100% client-side.
Kayak Size Calculator — Kayak Size + Paddle Length + Fit Planner
Free kayak size calculator: find the right kayak length and width for your height, weight and paddling style (recreational, touring, sea, whitewater, fishing, sit-on-top, tandem, inflatable). Includes kayak paddle length solver, weight capacity check and cockpit size chart. 100% client-side.
Kelvin to Celsius Converter (K to °C) - NR Tech Studio
Free Kelvin to Celsius converter with live two-way K to °C and °C to K conversion, adjustable precision, step-by-step working, landmark table and FAQs.
Kelvin to Fahrenheit Converter: K to °F Calculator with Formula, Table and Steps - nrtechstudio.com
Free Kelvin to Fahrenheit converter with live two-way K to °F calculation, the exact formula, step-by-step worked examples, a conversion table, and reference points like absolute zero, freezing and boiling water.
Kepler Third Law Calculator: Orbital Period, Radius & GM Solver
Free Kepler third law calculator: T² = 4π²a³/μ. Solve for orbital period T, semi-major axis a, or gravitational parameter μ, with preset μ for Sun, Earth, Moon and Mars plus mean orbital velocity v =
kg/cm2 to psi Converter: kgf/cm2 to psi, Both Directions
Free live converter: kg/cm2 (kgf/cm2) to psi and psi to kg/cm2, both directions. Exact factor 14.223343307, swap, precision control, worked derivation, conversion chart 0.5-20 kg/cm2, and 14 answered FAQs.
Kg to Gallons Converter | Kilograms to Gallons Mass Volume Calculator
Convert kilograms to gallons with density. Free kg to gallons calculator: water, milk, diesel, gasoline, oil, honey and custom density. US and imperial gallons, live 2-way conversion.
Kg to mL Converter: Kilograms to Milliliters with Density
Convert kilograms to milliliters and milliliters to kilograms using density. 8 substance presets (water, milk, oil, honey, flour, sugar, salt, butter) plus custom density, live two-way conversion, formula shown.
Kg to Newtons Converter — kg to N Calculator (Free, 2-Way) | nrtechstudio
Free kg to newtons calculator: convert kg to newtons and newtons to kg instantly. Supports N, kN, kgf, lbf, dyn, ozf, pdl, kip plus your weight on the Moon, Mars, and Jupiter. Formula F = m x g explained.
KG to Pounds Converter
The ultimate Kilograms to Pounds Converter, Lbs to KG Calculator, and Weight Unit Conversion Suite with 100% SEMrush keyword optimization.
Kg to Stones Converter: Kilograms to Stones and Pounds
Convert kilograms to stones and pounds instantly: 70 kg = 11 st 0.3 lb. Two-way live converter with stones+pounds breakdown, precision control, show-your-work steps, and a quick reference table.
Kidney Failure Risk Calculator (KFRE) — 2-Year & 5-Year CKD Risk Estimate
Free Kidney Failure Risk Equation (KFRE) calculator by Tangri et al. Estimate 2-year and 5-year kidney failure risk from age, sex, eGFR and urine albumin-to-creatinine ratio (ACR). Educational estimate only — not medical advice.
Kids Chore Chart Maker — Free Printable Chore Chart Builder with Reward Points Tracker
Build a free printable kids chore chart in minutes: pick age-appropriate chores (ages 3–12), track points with an interactive check-off grid, and set reward tiers with an ETA calculator. 100% client-side, no signup.
Kiln Firing Schedule Generator — Bisque & Glaze Ramp-Soak Schedules, Cone Chart & Firing Cost
Free kiln firing schedule generator: build ramp-soak schedules for bisque (cone 04/06) and glaze (cone 5/6/10) firings. Supports manual, digital, kiln-sitter, gas and microwave kilns. Includes Orton cone temperature lookup and an electric kiln firing cost estimator. 100% client-side — your data never leaves your browser.
Kinematic Viscosity of Air Calculator | Sutherland Model
Free kinematic viscosity of air calculator. Compute nu = mu/rho from temperature (Sutherland formula) and pressure (ideal gas), with unit conversions and a reference table.
kJ to BTU Converter
Convert kilojoules to BTU and BTU to kilojoules instantly. Uses the exact IT convention: 1 BTU(IT) = 1055.05585262 J, so 1 kJ = 0.9478171203 BTU. Live two-way conversion, precision control, derivation steps, quick tables, HVAC context.
kJ to Cal Calculator & Kilojoules to Kilocalories Converter
Interactive kJ to cal calculator, convert kJ to kcal, conversion kj en kcal, and kilojoules to kilocalories food nutrition tool.
Knit Crochet Lab — Gauge Calculator, Needle/Hook Converter Yarn Yardage
Free knit & crochet lab: knitting gauge calculator (swatch to cast-on stitches), pattern gauge adjustment, interactive US/UK/mm knitting needle & crochet hook size converter, yarn yardage estimator from Craft Yarn Council ranges, and a beginner project recommender. 100% private, works offline.
Knit Increase/Decrease Calculator — Increase & Decrease Evenly Across a Row
Free knit increase/decrease calculator: space increases or decreases evenly across a row or round, exclude edge stitches, get written row-by-row instructions. Works for kfb, M1, k2tog, ssk. 100% private, runs in your browser.
Knots to KPH Converter: Convert Knots to km/h Instantly (Free)
Free knots to kph converter. Convert knots to km/h instantly with an exact formula (1 knot = 1.852 km/h), multi-unit mode (mph, m/s, ft/s), conversion chart, Beaufort wind scale, and worked examples. 100% client-side.
Knots to MPH Converter: Knots to Miles per Hour Calculator
Free knots to mph calculator. Convert knots to miles per hour (and mph to knots) live, with multi-unit mode (knots, mph, km/h, m/s, ft/s), adjustable precision 0-10 decimals, show-your-work steps, a knots to mph chart, Beaufort scale, and boat and airplane speed context.
Knudsen Number Calculator
Free Knudsen number calculator: compute Kn = λ/L from the mean free path and characteristic length, or from kinetic theory (λ = kB·T/(√2·π·d²·P)). Classifies continuum, slip-flow, transition and free-
kPa to mmHg Conversion Calculator - Kilopascal to Millimeters of Mercury
Convert kPa to mmHg instantly with this free kilopascal to millimeters of mercury calculator. Live two-way conversion, mmHg to kPa, kPa to torr, conversion formula, chart, table, and blood pressure reference.
kPa to psi Converter: kilopascal to psi, Both Directions
Free live kpa to psi conversion tool: kilopascal to psi and psi to kPa, both directions. Exact factor 6.894757293168, swap, adjustable precision, quick kpa to psi chart, tire pressure examples, and 16 answered FAQs.
ksi to MPa Converter - Free ksi to MPa Calculator
Free ksi to MPa converter with live two-way conversion. Convert kilopounds per square inch (ksi) to megapascals (MPa), psi, kPa, GPa and Pa. Includes conversion factor, formula, quick chart, material strength tables and worked examples.
KSI to PSI Conversion Calculator
Free ksi to psi conversion calculator. Convert kilopounds per square inch to psi and back, plus MPa, kPa and Pa. Exact formula: 1 ksi = 1000 psi. Includes conversion chart, worked examples and FAQ.
Kubernetes YAML Validator & Lint Tool
Free online Kubernetes YAML validator and YAML lint tool to check Kubernetes manifests for syntax errors, schema conformance, and security best practices.
kW to Joules Converter — Power × Time to Energy (J, kJ, kWh, BTU)
Convert kilowatts to joules with time: E(J) = 1000 × kW × seconds. Bidirectional kW↔J calculator, kJ/MJ/Wh/kWh/BTU/kcal outputs, practical presets, worked examples. Free, 100% client-side.
kW to kJ Converter — Kilowatts to Kilojoules Calculator (Free, No Sign-up)
Free kW to kJ converter: turn kilowatts × time into kilojoules. Reverse kJ → kW mode, power-rate converter (kJ/h, BTU/h, kcal/h, MJ/h), energy converter (MJ, kWh, BTU, kcal), worked examples & formulas. 100% client-side.
kW to kWh Calculator: Convert Kilowatts to Kilowatt-Hours
Free kW to kWh calculator: enter power in kW plus time to get energy in kWh (kWh = kW x hours). Reverse mode converts kWh to average kW, with electricity cost estimates and household appliance presets.
kW to MW Converter | Kilowatt to Megawatt Calculator
Convert kW to MW and MW to kW instantly. Live two-way kilowatt to megawatt converter with watts and gigawatts, formula, quick table, and worked examples. 1 MW = 1,000 kW exactly.
kW to Volts Calculator — DC, Single-Phase & 3-Phase Converter
Free kW to volts calculator: convert kilowatts to volts for DC, single-phase and three-phase (line-to-line / line-to-neutral) circuits with power factor. Also volts to kW, watts to volts mode, and a common-voltage current solver. 100% client-side.
kW to Wh Converter — Kilowatts to Watt-Hours Calculator | nrtechstudio.com
Convert kW to Wh with time: E(Wh) = P(kW) × 1000 × t(h). Free calculator with reverse mode, battery Wh from volts × amp-hours, UPS runtime sizing, worked examples, and honest limitations. 100% client-side.
Liters to Gallons Converter (US and Imperial)
Convert liters to gallons and back with this free l to gal calculator. 1 liter = 0.2642 US gallons or 0.2200 imperial gallons. Formula, quick liters to gallons chart, worked examples, and 16 FAQs.
LFPR Calculator — Labor Force Participation Rate
Calculate the labor force participation rate (LFPR): labor-force ÷ working-age-population × 100% formula, employed/unemployed breakdown, two-period comparator, and target solver. Free, 100% client-side.
Lamp Post Size Calculator — Height, Spacing, Lumens & Cost
Free lamp post size calculator: mounting height, spacing, lumens and watts, foundation and concrete, solar vs wired planning, placement, and cost estimates.
Land Loan Payment Calculator — Land & Lot Loan Payments
Free land loan payment calculator: estimate monthly payments, total interest and balloon balance for raw land and improved lot loans. Land loans need 20-50% down, carry higher rates and shorter terms (5-20 years) than mortgages.
Large Exponent Calculator — Big Power, Modular Exponentiation & Last Digits | nrtechstudio
Compute huge powers exactly with BigInt (digit count, scientific notation), run fast modular exponentiation a^b mod m with step-by-step square-and-multiply, and find last digits of giant powers. 100%
Laser Beam Divergence Calculator
Free laser beam divergence calculator: compute Gaussian beam divergence theta = M2*lambda/(pi*w0). Solve for divergence, wavelength, waist or M2, with Rayleigh range, full angle and beam parameter pro
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How to Use the Tools Directory
Every tool is a single interactive page: enter your inputs, get instant results, no account needed. Use the search box (shortcut: press /) to jump straight to a tool, or browse categories when you are exploring. Each card links to the tool's permanent URL, which you can bookmark or share.
Because all computation happens in your browser, the tools are fast, private, and free forever. If a result looks wrong, use the one-click report control on the tool page so it can be fixed.
Tool Categories at a Glance
| Category | What you will find | Example tasks |
|---|---|---|
| Developer | Encoders, formatters, regex, network tools | Format JSON, test regex, subnet a network |
| Finance | Tax, loans, salary, investing | Estimate tax brackets, amortize a loan |
| Home improvement | Estimators, measurements, materials | Size a wire, estimate paint or flooring |
| Health & fitness | Body metrics, nutrition, workouts | Track BMI, plan calories, score fitness tests |
| Math & science | Converters, geometry, statistics | Convert units, solve triangles |
| Text | Counters, sorters, generators | Count words, alphabetize a list |
| Color | Pickers, converters, checkers | Convert HEX to RGB, check contrast |
| Everyday life | Cooking, travel, automotive, pets | Convert recipes, plan fuel costs |
Popular Tasks and Where to Start
| I want to... | Start with | Why |
|---|---|---|
| Convert between number bases | Binary Converter | Step-by-step base conversion with charts |
| Validate and format data | JSON Formatter | Pretty-print and check JSON instantly |
| Count words for an essay | Word Counter | Words, characters, reading time |
| Check password strength | Password Strength Meter | Entropy-based strength scoring |
| Grade text readability | Readability Score | Flesch-Kincaid and grade levels |
| Audit color contrast | Accessibility Checker | WCAG contrast ratios in one click |
Tools Directory FAQ
What is the NRTechStudio tools directory?
It is a free catalog of more than 2,700 interactive web tools: calculators, converters, generators, and checkers for developers, finance, home improvement, health, education, and everyday tasks.
Are all the tools really free?
Yes. Every tool in the directory is free to use with no sign-up, no trial, and no paywall. They run entirely in your browser.
Do I need to create an account?
No. There are no accounts, logins, or subscriptions. Open a tool and use it immediately.
Is my data private when I use these tools?
Yes. The tools are 100% client-side: your inputs are processed by JavaScript in your own browser and never sent to a server.
How do I find the right tool?
Use the search box at the top of the directory (press / to focus it), or browse by category. Every tool card shows a short description of what it computes.
Do the tools work on mobile?
Yes. The directory and the tools use responsive layouts that adapt to phones, tablets, and desktops.
How many tools are there?
The directory holds more than 2,700 tools and grows regularly as new calculators and converters are published.
Can I request a new tool?
Yes. Each tool page has a report/feedback control you can use to request features or new tools; requests help prioritize what gets built next.
Are the tools accurate?
Calculators use published formulas and reference data (tax tables, NEC ampacity, standard conversions). Each tool page documents its method, and issues can be reported in one click for a fix.
Do tools work offline?
Once a tool page has loaded, most tools keep working without a connection because the logic is client-side JavaScript. The directory search needs the page loaded first.
What categories are covered?
Developer utilities, finance and tax, home improvement, health and fitness, math and science, text tools, color tools, networking, education, and everyday life calculators, among others.
Can I bookmark or share a tool?
Yes. Every tool has its own permanent URL under nrtechstudio.com/tools/, which you can bookmark or share directly.
Is there an API for these tools?
The tools are interactive web pages, not API endpoints. The underlying math is plain JavaScript you can inspect in the page source.
Why do some tools show ratings?
Ratings aggregate user feedback to surface the most trusted tools and flag pages that need fixes or better explanations.
How often are new tools added?
New tools are published on a continuous pipeline, prioritized by measured search demand and by user requests from the feedback controls.
Who builds these tools?
NRTechStudio, an independent tools studio focused on free, private, client-side utilities that respect user privacy.