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.
Stillbirth Risk Factor Calculator (Educational)
Stillbirth risk factor explainer (CDC, Lancet, JAMA): checklist of 10 documented risk factors with educational context, pregnancy warning signs, and a guide for discussing with your doctor or midwife.
Stock Average Calculator
Free stock average calculator: average cost per share across lots, average-down planner, break-even price and unrealized P/L.
STOP-Bang Calculator — Sleep Apnea Risk Screening Tool
Free STOP-Bang calculator: answer 8 yes/no questions to screen for obstructive sleep apnea risk (low, intermediate, high) with the validated Chung et al. scoring. Screening aid only, not a diagnosis.
Stopping Distance Calculator - Braking, Reaction and Total Distance
Compute braking distance (d = v^2/(2*mu*g)), reaction distance and total stopping distance for dry, wet and icy roads, compare surfaces, or find the m
Stopwatch Online — Free with Lap Times
Free online stopwatch with lap times, centisecond precision, keyboard shortcuts, fastest/slowest lap highlights and CSV export. 100% client-side.
Storage Unit Size Calculator — What Size Do I Need? (5×5 to 10×30)
Storage unit size calculator: what size do I need? Estimate from 120+ household items with a 10-20% buffer, stacking planner and climate-control advic
Reverse Characters — Unicode-Safe String Reverser
Standalone reverse-characters tool. Reverse a whole string, each word, or each line with Unicode-aware grapheme reversal (emoji and ZWJ sequences stay intact). 100% client-side.
Reverse Words & Sentence Generator
Standalone professional reverse words generator, reverse word order tool, and sentence reverser. Reverse words in string online, reverse text in word, and explore reversed words algorithms with zero AI slop.
String to Base64URL Encoder
Standalone one-way string-to-Base64URL encoder. UTF-8 aware, padding toggle, per-chunk byte mapping, batch mode. 100% client-side.
Stress Concentration Factor (Kt) Calculator — Hole, Fillet, Notch + Kf
Free stress concentration factor calculator: Kt for a hole in a plate (Heywood), shoulder fillets in tension & bending (Peterson chart curve-fits), notches (Inglis), plus fatigue Kf via Neuber notch sensitivity q. 100% in-browser, no sign-up.
String Compare & Text Diff Tool
High-performance online string compare and text diff tool. Compare two strings, find differences between texts, and perform word-to-word comparison online.
String Length Calculator
Advanced character length calculator, UTF-8 byte size counter, and string memory analyzer for developers.
String Padding Tool
Professional String Padding Tool Online, Left/Right/Center Text Formatter, and Zero-Pad Generator with 100% SEMrush keyword optimization.
String to Snake Case
Universal Convert String to Snake Case Tool, Naming Convention Transformer, and Identifier Sanitizer with 100% SEMrush keyword optimization.
String To Json
Stripe Fee & Payout Calculator
Free online Stripe fee calculator to compute credit card processing deductions (2.9% + $0.30), international card fees, and exact gross invoices.
Stroke Volume Calculator (SV = EDV − ESV, SV = CO/HR, SVI) — nrtechstudio
General stroke volume calculator: SV = EDV − ESV, SV = CO/HR, and stroke volume index
Student Loan Calculator — Payment, Payoff, IDR, PSLF & Refinance Estimator
Free student loan calculator: estimate monthly payments, payoff date with extra payments, income-driven repayment (IBR, PAYE, RAP), PSLF timeline, federal vs private comparison, and refinance break-even — with year-by-year amortization and CSV export.
Sub Business Days
Subtract working business days from a date.
Subtract Years from Date Calculator
Free subtract years from date calculator, minus years from a date, date minus years calculator, years ago from today calculator, date calculator minus years, how to subtract years from a date, leap year date subtraction, february 29 minus 1 year handling, subtract years from date excel and edate subtract years formula guide, past date calculator years, date n years earlier calculator.
IPv4 Subnet Mask & CIDR Calculator
Free online IPv4 subnet calculator to determine network address, broadcast IP, usable host range, CIDR prefix (/8 to /32), and wildcard mask.
Subtitle Shifter — Fix SRT Sync: Shift Timing, Drift Resync & FPS Convert (Free)
Free online subtitle shifter: shift SRT subtitles by milliseconds, fix progressive drift with two-point resync, convert 23.976↔24↔25 fps, repair overlaps and validate SRT files. 100% client-side — your files never leave your browser.
Sugar Intake Calculator — Daily Limit, WHO & AHA Guidelines | nrtechstudio
Free sugar intake calculator: find your daily limit from WHO (<10% of calories, ideal <5%) and AHA guidelines (men 36 g, women 25 g), convert gr
Sun Angle Calculator — Solar Altitude & Azimuth, Sunrise/Sunset
Calculate accurate sun angle (solar altitude & azimuth) from latitude, longitude, date, and timezone. Includes sunrise, sunset, solar noon, declination, equation of time, day length, shadow length estimate, and hourly table.
Sunroom Size Calculator — 7 Ways to Plan Your Sunroom
How big should a sunroom be? Free 7-mode calculator for glazing %, HVAC BTU per sq ft, foundation cost, permits, setbacks and furniture layout.
Surface Tension Calculator
Free surface tension calculator: capillary rise h = 2γcosθ/(ρgr), surface tension from capillary data, Young-Laplace droplet and soap bubble pressure,
Surfboard Volume Calculator — Liters by Dimensions, Ideal Volume Finder & Quiver Compare
Free surfboard volume calculator: estimate liters from dimensions with per-board-type coefficients calibrated against real published boards, find your ideal volume with 3 methods side-by-side, reverse-solve dims from liters, compare your quiver, and size boards for kids. 100% private — runs in your browser.
Tool - Surname Generator & Ultimate Name Generator
Multi-genre name generator suite featuring surname generator, fantasy character name generator, RPG game name generator, American name generator, and name and email generator.
CCTV Storage Calculator — NVR/DVR Storage Planner Camera Recording Time
Free CCTV storage calculator & NVR/DVR storage planner: plan multi-camera storage by resolution, fps, codec (H.264/H.265), motion detection % and retention days. Vendor bitrate presets (Dahua, Hikvision, Axis, Bosch), recording-time inverse, GoPro/dashcam SD-card recording time, codec comparison. 100% client-side.
SUVAT Calculator
Free SUVAT calculator: solve the 5 equations of motion for s, u, v, a or t. Enter any 3 known values, get the missing one with full working shown. Sup
SVG Code to File – SVG Viewer, Converter & Editor
Online SVG code to file converter and viewer. Paste SVG code, preview it live, download as .svg file, convert to PNG/Base64, and explore React/React Native SVG usage.
Free SVG Converter & Vector Creator
Interactive raster image to SVG converter, transforming PNG, JPG, and logos into scalable vector graphics with full color support.
SVG Optimizer — Minify SVG Code Online
Free online SVG optimizer: minify SVG code, remove metadata and bloat, round path precision, with live preview and before/after size comparison. 100% client-side.
SVG Placeholder — Generate Custom SVG Placeholder Images
Free online SVG placeholder generator: custom dimensions, solid or gradient background, custom text, border radius and grid/diagonal patterns. Copy SVG code, data URI, HTML or CSS snippet, or download the .svg file. 100% client-side.
SVG to Base64 — Encode SVG as Data URI
Free online SVG to Base64 converter: paste SVG code and get a Base64 or URL-encoded data URI, CSS background-image snippet, live preview and download. 100% client-side.
SVG to Code Converter & Vector Component Generator
Free online SVG to code converter. Convert any SVG document into React JSX, React Native, inline HTML SVG, and CSS Data URI. Learn how to create an SVG file, extract SVG from developer tools, and download SVG code to SVG file.
SVG to JSX & React Component Converter
Standalone professional SVG to JSX converter, React SVG transformer, and React Native SVG component builder. Convert SVG code to React component with clean camelCase attributes and zero AI slop.
Swamp Cooler Size Calculator — What CFM Does Your Home Need? | nrtechstudio.com
Swamp cooler size calculator: find the right CFM for your home or room with the 30 air-changes/hour rule, exhaust sizing, unit picker and climate chec
Swarm Trap Size Calculator — Ideal Volume, Entrance & Lure Guide
Free swarm trap size calculator: check your trap volume against Seeley's 40-liter ideal, size the entrance hole (~15 cm²), dose lemongrass oil lure, score your trap placement, and follow a monitoring checklist. 100% client-side.
SWG to mm Converter — SWG to mm² Wire Gauge Calculator | nrtechstudio
Convert SWG to mm, mm², inches and circular mils (7/0–50), reverse-convert mm/mm² to SWG, browse the full searchable SWG table with reference ampacity, and size wire with a 3% voltage-drop advisor. 100% client-side.
Swim Pace Lab — CSS Calculator, Pace Converter, Training Zones & Race Predictor
Free swim pace lab: convert pace per 100m / 100 yards / 50m, calculate Critical Swim Speed (CSS) from 400+200 or 1500+400 time trials, get 5 CSS training zones, predict triathlon swim-leg times (sprint, Olympic, 70.3, Ironman), adjust pool pace for open water, and convert stroke paces. 100% client-side.
Swine Gestation Calculator — Farrowing Date, 3-3-3 Calendar & Prep Checklist
Free swine gestation calculator: enter the breeding date to get the farrowing window (112–116 days, avg 114), countdown, pregnancy timeline, litter guide, farrowing signs, and preparation checklist.
Swing Set Size Calculator — Yard Fit, Fall Zone & Mulch Planner
Free swing set size calculator with 7 modes: yard fit, 6-ft safety clearance, fall zone, mulch volume and budget sizing. Plan the right playset.
SWR Lab — SWR Calculator, Impedance Matching & Balun Designer
Free SWR lab suite: SWR ↔ return loss ↔ reflection coefficient converter, SWR-adjusted coax loss calculator, L-network impedance matching calculator, toroid turns designer, ugly-balun & ferrite choke advisor, mismatch loss calculator. 100% private, runs in your browser.
Synodic Period Calculator | 1/S = |1/P minus 1/E|
Free synodic period calculator: S = 1/|1/P - 1/E|. Planet synodic periods vs Earth (Mars 780d, Venus 584d), Moon synodic month 29.53d phase calculator
T/E2 Ratio Calculator — Testosterone to Estradiol Ratio + Unit Converter
Calculate your testosterone-to-estradiol (T/E2) ratio with automatic unit conversion (ng/dL ↔ nmol/L, pg/mL ↔ pmol/L), reverse calculator for target r
Table Lamp Size Calculator — Bedside, End Table & Desk Lamp Sizing | nrtechstudio.com
What size table lamp for a nightstand? Free bedside, end table, console & desk lamp size calculator with shade proportions and glare check.
Take-Home Pay Calculator (2026) — Net Paycheck After Federal, State & FICA Taxes
Free 2026 take-home pay calculator: enter salary or hourly wage and see your net paycheck after federal income tax, FICA (Social Security + Medicare), state tax (CA, NY, TX, FL, custom), 401(k), HSA and deductions — with a full gross-to-net breakdown.
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Try a different keyword like "calculator", "planner", "converter" - or pick a category above.
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.