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.
EBITDA Multiple Calculator — Company Valuation (EV = EBITDA × Multiple)
Free EBITDA multiple calculator: compute enterprise value from EBITDA × multiple, reverse solver, 2-company comparator, sensitivity analysis, and industry EV/EBITDA reference table. Educational estimate, not investment advice.
ECDSA Key Generator
High-Security ECDSA Key Pair Generator, Crypto Elliptic Curve Key Creator, and Digital Signature Playground with 100% SEMrush keyword optimization.
ECG Boxes to Seconds Converter — Small & Large Box Time Calculator
Convert ECG paper boxes to seconds and milliseconds. Standard 25 mm/s and 50 mm/s paper speeds. 1 small box = 0.04 s, 1 large box = 0.2 s. Two-way con
ECG Heart Rate Calculator — 1500, 300 & 6-Second Method
Calculate heart rate from an ECG strip: the 1500 method (small boxes), 300 method (large boxes), 300-150-100-75-60-50 count-off, and the 6-second QRS
EVA (Economic Value Added) Calculator — Compute a Company’s Economic Profit
EVA (Economic Value Added) calculator: compute economic profit from NOPAT, WACC, and invested capital. Compare ROIC vs WACC, breakeven WACC solver, and 2-company comparison. Free, 100% in your browser.
Ed25519 Key Gen
Generate Ed25519 cryptographic key pairs.
eDPI Calculator — DPI × Sensitivity, cm/360 & Cross-Game Converter | nrtechstudio.com
Free eDPI calculator: compute effective DPI from mouse DPI × in-game sensitivity, reverse it to find sensitivity for a target eDPI, convert cm/360, and convert sensitivity between CS2, Valorant and Overwatch.
EER Calculator (Estimated Energy Requirement) — IOM/DRI Equations | nrtechstudio
Free EER calculator using the Institute of Medicine (IOM) Dietary Reference Intake equations for adults 19+. Enter age, sex, weight, height, and activ
Effective Interest Rate Calculator
Free effective interest rate calculator: true yearly cost of a loan including origination and other fees (simple total-cost method), add-on installment loan effective rates, and side-by-side loan comparison.
Heat Exchanger Effectiveness–NTU Calculator (ε-NTU Method) — nrtechstudio.com
Free effectiveness-NTU method calculator: compute ε from NTU & Cr for 5 flow arrangements, NTU from target ε, actual heat rate, outlet temperatures of both fluids, and heat exchanger area sizing. 100% in your browser.
Egg Freezing Calculator — Live Birth Chances from Frozen Eggs (Oocyte Cryopreservation)
Estimate your chance of a live birth from frozen eggs by age at freezing and number of oocytes. Binomial model calibrated to Doyle 2016 & Goldman
EIC Calculator 2026 — Earned Income Tax Credit Estimator
Free 2026 EIC/EITC calculator: estimate your Earned Income Tax Credit by income, filing status and qualifying children. IRS Rev. Proc. 2025-32 figures. 100% client-side.
EIRP Calculator — Effective Isotropic Radiated Power (eirp calculator)
Online EIRP calculator: compute Effective Isotropic Radiated Power from transmitter power, antenna gain, and line loss. 4-way solver, ERP↔EIRP converter, regulatory limit table, Friis distance estimation.
Elastic Constants Calculator - Convert E, ν, G, K, λ, M
Convert between all isotropic elastic constants: Young's modulus (E), Poisson's ratio (ν), shear modulus (G), bulk modulus (K), Lamé's first parameter (λ) and P-wave modulus (M). Enter any two, get th
Spring Elastic Potential Energy Calculator (U=½kx²)
Spring elastic potential energy calculator U=½kx²: find energy, spring constant k, or displacement x — plus series & parallel springs, unit conversion, and solution steps.
Point Charge Electric Field Calculator — E = kQ/r²
Free point charge electric field calculator: compute field E = k·Q/r², solve for charge Q, solve for distance r, and 1D superposition of three collinear charges. CODATA 2018 Coulomb constant. 100% runs in your browser.
Electric Motor Torque Calculator — HP, RPM & Torque
Free electric motor torque calculator. Solve for torque (T = HP × 5252 / RPM), horsepower, or RPM in imperial (lb-ft) or metric (N·m, kW) units. Instant, accurate, no sign-up.
Electric Potential Calculator — V=kQ/r, Potential Energy & Potential Difference
Free electric potential calculator: compute V=kQ/r in all directions (±), potential energy U=qV, potential difference ΔV & work W=qΔV, plus superposition of N charges. 100% in the browser.
Electric Vehicle Fuel Savings Calculator — Gas vs EV Annual Cost Comparison
Compare annual fuel costs: gasoline car vs electric vehicle. Enter miles driven, MPG, gas price, EV efficiency and electricity price to see yearly savings, 5-year savings and payback period. Free, 100% client-side.
Electrical Box Fill Calculator — NEC 314.16 Box Fill & Box Sizer
Free NEC 314.16 electrical box fill calculator: conductors, devices, clamps, grounds and 2023 terminal blocks. Check any box or size the minimum box.
Electrical Unit Converter — Ohm's Law, Resistor Codes & Wire Sizes | nrtechstudio
Free electrical unit converter: volts, amps, ohms, farads & more, plus an Ohm
Electricity Convert – Electrical, Metric & Scientific Converter
Electricity convert, meters to feet conversion chart, how to convert mtr to feet, how to convert meter to ft, measure conversion chart, convert kg to l, how to change meter to feet, number conversion, distance conversion table, metric to standard calculator, how to change centimeters to meters, metric imperial conversion chart, how to turn meters into feet, scientific unit converter, how long is a meter in ft, how long is a meter to a foot, convert measurement chart, base converter online, mass to volume converter, meter to kg conversion, convert meters to kilograms, conversion calculator imperial to metric, base two converter, data converter calculator, tabular calculator, centimeters to grams converter, metres to feet conversion chart, conversion chemistry calculator, conversion for cubic meters, metric and imperial length tool.
Electron Speed Calculator — Classical & Relativistic
Calculate electron speed from kinetic energy (eV, keV, MeV, J) with the classical formula v=√(2E/m) and the relativistic v=c√(1−1/γ²). Shows β, γ, and an honest marker of when the relativistic regime is required. Two-way solver.
Ellipse Circumference Calculator — Ramanujan I & II Approximations + Exact (AGM) | nrtechstudio
Compute ellipse circumference (perimeter of ellipse) with Ramanujan I & II approximations and the exact value via elliptic integral (AGM). Compare per-method error + bonus area πab and SVG diagram.
ELSS Calculator - Return Projection, 80C Tax Benefits & 3-Year Lock-in Tracker
Free ELSS calculator: lumpsum & SIP projections, Section 80C tax savings up to Rs 1.5 lakh, ELSS vs PPF vs NSC comparison, and track the 3-year lock-in of each SIP installment.
SPF, DKIM DMARC Generator — Free Email Authentication Studio (3-in-1)
Free 3-in-1 email authentication studio: SPF record generator with 10-lookup-limit simulator, real DKIM key-pair generator (RSA via WebCrypto), and DMARC record builder with RFC 9989 (DMARCbis) support. 100% client-side — your domain data never leaves your browser.
Email Extractor & Online Email Scraper Tool
Free online email extractor to extract email addresses from text, web pages, or documents. Bulk email extractor, email scraper, and email address extractor with instant regex-powered results.
Email Header Analyzer — Check SPF, DKIM, DMARC & Detect Phishing (Free)
Free online email header analyzer. Paste raw email headers to check SPF, DKIM & DMARC authentication, trace the Received chain hop by hop, and detect phishing & email spoofing. 100% client-side — your headers never leave your browser.
Email to MD Link — Free Mailto Markdown Link Generator
Free mailto link generator: turn any email into a Markdown [text](mailto:) link with subject, body, CC/BCC, escaping & obfuscation. 100% client-side.
Email Validator — Check Email Format & Syntax
Free online email validator: RFC 5322 syntax check with local-part/domain/TLD breakdown, domain typo suggestions, disposable email detection, role-account flags, and bulk list validation. 100% client-side.
Fast YouTube Embedder & Responsive Video Code Generator
Free fast YouTube embedder and video embed code generator. Create responsive YouTube iframes, embed playlists, configure autoplay, convert YouTube link to embed link, and generate clean HTML/React embed codes.
Emergency Fund Calculator — How Much to Save by Job Type | nrtechstudio.com
Free emergency fund calculator: risk-based targets by job type (stable employee, freelancer, contract, single-income), essential-expense builder, savings plan, tier system and emergency drain simulator. 100% client-side, private, no signup.
Emoji Remover — Remove All Emojis from Text Online
Free online emoji remover: paste text and strip every emoji (faces, flags, ZWJ families, keycaps, skin tones) in one click. 100% client-side.
Empty Line Remover — Remove Blank Lines from Text
Free empty line remover: delete blank lines from text or compact them to one. Whitespace-only detection, trailing trim, live stats & undo — client-side.
EMV (Expected Monetary Value) Calculator — Compute Expected Monetary Value & EVPI
Free EMV calculator: compute Expected Monetary Value for one decision, compare 2 alternatives, and compute EVPI (value of perfect information). Includes formulas, worked examples, an interpretation table, and FAQ.
D&D 5e Encounter Difficulty Calculator — XP Thresholds & Multiplier
Free D&D 5e encounter difficulty calculator. Enter your party and monsters to get adjusted XP, the encounter multiplier, and an Easy / Medium / Hard / Deadly verdict using the official 2014 XP threshold tables.
Ending Inventory Calculator: FIFO, LIFO, Weighted Average
Compute ending inventory with FIFO, LIFO, and weighted-average methods. Complete with COGS, gross profit, a 3-method comparator, and verified examples.
Energy Consumption Calculator — kWh per Device & Household Total | nrtechstudio
Estimate your home's energy consumption in kWh. Add appliances (watts x hours x days), see daily/weekly/monthly/yearly kWh per device, household totals, and a ranking of your biggest energy users. No
Energy Conversion Calculator Online
Free energy conversion calculator. Perform the conversions between energy units: joules, kWh, kJ, kcal, MWh, BTU. Energy unit converter, convert energy, joule conversions, joule to kwh, kj to kwh conversion, kwh to joules calculator, energy conversion chart, convert joules to kwh, joule to kcal converter, kilowatt to joules conversion, convert kj to kwh.
Energy Cost Calculator -- kWh to Cost (Flat, Tiers, Time-of-Use) | nrtechstudio.com
Free energy cost calculator: convert watts and kWh to electricity cost with flat tariffs, tiered slabs, time-of-use rates, budget reversal, efficiency comparisons, and country tariff comparison. 100% client-side, no data leaves your browser.
Energy Density of Electric and Magnetic Fields Calculator
Free energy density calculator: u_E = ½ε₀E² and u_B = B²/(2μ₀) with every solver direction, combined total + ratio, a plane-wave equality proof (E = cB), real-world presets and step-by-step work. 100%
Photon Energy to Wavelength Converter — eV to nm Calculator | nrtechstudio.com
Free photon energy to wavelength calculator. Convert eV, joules, kJ/mol to wavelength (nm, µm, Å) and back. Get frequency, wavenumber, spectrum band and visible color. E = hc/λ, 100% in your browser.
Energy Unit Converter — Joules, kWh, BTU, kcal + Cost & Fuel Calculator | nrtechstudio
Free energy unit converter: joules, kJ, calories, kcal, Wh, kWh, MWh, eV, BTU, therm, ft-lb, tonne of oil equivalent. Plus electricity cost calculator, food energy (kcal↔kJ) with exercise equivalents, fuel equivalents, and a mini home energy audit. 100% client-side.
Energy Units Converter & kWh to Therm Calculator
Free online energy units converter and kWh to therm calculator. Convert kilowatt-hours, US therms, BTU, megajoules, and natural gas volume accurately.
Engagement Rate Calculator — Instagram, TikTok & More | nrtechstudio.com
Free engagement rate calculator: compute per-post or profile-average ER for Instagram, TikTok, X, Facebook and YouTube. Formula: (likes + comments + shares + saves) / followers x 100. Benchmark tiers for nano, micro, macro and mega accounts.
Engine Displacement Calculator — Bore × Stroke to CI, CC & Liters (Free)
Free engine displacement calculator: enter bore, stroke and cylinder count to get displacement in cubic inches, cc and liters. Includes reverse solver (find bore/stroke/cylinders), bore/stroke ratio, CFM airflow estimate and famous engine presets. 100% client-side.
Engine Hours to Miles Converter | Fleet Maintenance Estimator
Convert engine hours to equivalent miles (and miles back to hours) with duty-cycle presets for semi trucks, vans, and equipment. Free fleet maintenance scheduling helper.
Engineering Notation Converter — Notasi Engineering & Prefix SI | nrtechstudio.com
Two-way engineering notation converter: numbers ↔ engineering notation (exponents in multiples of 3) with SI prefixes p, n, μ, m, k, M, G, T, plus a scientific notation comparison. Single, batch, and prefix-picker modes.
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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.