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.
10/1 ARM Calculator — Fixed 10 Years, Then Adjustable
Free 10/1 ARM calculator: monthly payment for the 10-year fixed period, remaining balance at reset, new payment at your assumed rate, payment shock, worst-case payment at the lifetime cap, and a full amortization schedule.
10 Binary Number & Numeral Systems Converter
Free online decimal to binary converter with step-by-step division, base 5 calculator, numeral systems converter, and binary conversion charts.
100 Amp Wire Size Calculator — NEC Table 310.16 Ampacity
What size wire for 100 amps? NEC Table 310.16 ampacity calculator: copper vs aluminum, 60/75/90°C columns, conduit derating, and breaker recommendation. Free, no sign-up.
12V Wire Size Calculator — AWG by Amps, Length & Voltage Drop (12/24/48V) | nrtechstudio.com
Free 12V wire size calculator: enter amps, one-way length and system voltage (12/24/48V) to get the smallest copper AWG that passes ampacity and keeps voltage drop ≤3%. Includes a voltage drop lab, ampacity table, and worked examples. 100% client-side, no signup.
3D Print Cost Calculator (FDM + Resin) — Free Print Quoting Tool
Free 3D print cost calculator for FDM & resin. Model filament, electricity, machine wear, labor, support & purge waste, failure rate and quoting margin — all in your browser.
Buy a 3D Printer vs Print Service: Break-Even Calculator (Free)
Compare the total cost of buying your own 3D printer vs ordering 3D print services. Calculate the break-even point (grams & months), cost comparison chart, and sensitivity table — 100% in your browser.
3kg to Lbs Converter
High-precision 3kg to Lbs Converter, Kilograms to Pounds & Ounces, Weight Converter Unit Table.
3x Rent Rule Calculator — Income Needed for Rent & Max Affordable Rent (Free)
Free 3x rent rule calculator: enter your rent to find the gross income landlords require, or enter your income to find the maximum rent you can afford. Includes the NYC 40x rule, adjustable 2.5x–4x multiplier, and gross/net conversion. 100% private — runs in your browser.
4Ts Score Calculator — HIT Pretest Probability
Free 4Ts Score calculator: estimate the pretest probability of Heparin-Induced Thrombocytopenia (HIT) from 4 categories — Thrombocytopenia, Timing, Thrombosis, oTher causes. Live 0–8 score with Low / Intermediate / High interpretation. An educational tool, not a substitute for clinical assessment.
50/30/20 Rule Calculator: Split Your Paycheck into Needs, Wants & Savings
Free 50/30/20 rule calculator: split monthly net income into 50% needs, 30% wants, and 20% savings. Includes a budget compliance check, custom ratios, and what-if scenarios.
529 College Savings Calculator — Monthly Solver, State Tax Benefits & 529 vs Taxable (Free)
Free 529 college savings calculator: growth projector with expense-ratio drag, monthly savings solver for inflation-adjusted college costs, all-50-state tax benefit table, 529 vs taxable account comparison, and 5-year superfunding analyzer. 100% private — runs entirely in your browser.
5K Pace Calculator — Target Time to Pace, Splits & Pace Chart
Free 5K pace calculator: convert a 5K target time to pace per km and per mile with cumulative km splits, predict 5K finish time from pace, and browse a 15:00–40:00 pace chart.
6-Minute Walk Test Calculator — Predicted Distance, % Predicted & ATS Protocol | nrtechstudio.com
Free 6-minute walk test (6MWT) calculator: predicted distance from Enright, Troosters & Jenkins reference equations, percent predicted, lower limit of
A Body Shape Index (ABSI) Calculator — Free, Private
Free A Body Shape Index (ABSI) calculator: enter waist, height, weight, age and sex to get your ABSI score, age/sex-adjusted z-score vs the NHANES ref
A-Frame Size Calculator — 7 Ways to Size Your A-Frame Cabin
Free 7-mode A-frame cabin size calculator: triangle geometry, usable floor (5 ft rule), loft, deck, kitchen/bath fit, occupants, snow-load rafter chec
A-a Gradient (AaDO2) Calculator + PaO2/FiO2 Ratio
Calculate the alveolar–arterial oxygen gradient (A-a gradient / AaDO2) from the alveolar gas equation: PAO2 = FiO2×(Patm−PH2O) − PaCO2/R. Includes age-based normal limits, PaO2/FiO2 ratio, Berlin ARDS criteria, and inverse FiO2 mode. Free educational tool.
A/B Test Calculator: Significance Test and Sample Size Planner | NRTechStudio
Free A/B test calculator: enter visitors and conversions for variants A and B to get conversion rates, uplift, a two-proportion z-test p-value, a significant-or-not verdict, and the confidence interval — plus a sample size planner.
ABI Calculator — Ankle-Brachial Index (Free, Private)
Free ankle-brachial index (ABI) calculator. Enter dorsalis pedis, posterior tibial and brachial systolic pressures — get per-leg ABI, interpretation ranges, and educational next steps. 100% client-side, no data leaves your browser.
Absence Percentage Calculator (School & Work) — nrtechstudio
Free absence percentage calculator for school and work. Enter days absent and total days to get absence %, attendance rate, interpretation bands, and how many days you can still miss. 100% client-side — your data never leaves your browser.
Absolute Difference Calculator |a−b| + Steps
Free absolute difference calculator: enter two numbers to get |a−b| with step-by-step breakdown, worked examples, and how it differs from percent difference.
Absolute Value Calculator - Find |x| with Number Line
Free absolute value calculator: enter x to get |x|, see the piecewise definition (|x| = x for x >= 0, |x| = -x for x < 0), worked steps, a number line showing x and |x|, and key properties.
AC Wattage Calculator — Real, Apparent & Reactive Power (1-Phase, 3-Phase, PF Correction)
Free AC wattage calculator: solve P=V×I×PF for any missing variable, 3-phase power (√3×V_LL×I×PF), and size power-factor correction capacitors. Real (W), apparent (VA), reactive (VAR).
Accent Chair Size Calculator — 7 Ways to Find Your Perfect Chair
What size accent chair do you need? Free 7-mode calculator: seat height, depth, width, sofa match, room fit, walkway clearance and size class. Inches
Web Accessibility & Contrast Ratio Checker
Free web accessibility checker and WCAG contrast ratio checker. Verify colour contrast accessibility, test Section 508 compliance, and preview text legibility.
Accounting Profit vs Economic Profit Calculator — Calculate & Compare (Free)
Free accounting profit vs economic profit calculator: compute accounting profit (revenue minus explicit costs) and economic profit (minus opportunity cost). Includes a warung kopi SME example, concept comparison table, step breakdown, and FAQ. 100% runs in your browser.
Accrual Ratio Calculator (Sloan 1996) — Measure Company Earnings Quality
Compute Sloan (1996) accrual ratio: (net income − operating cash flow) ÷ total assets. Measure earnings quality, accrual vs cash decomposition, interpretation table, examples, and FAQ.
ACFT Score Calculator — Army Combat Fitness Test (6 Events)
Free ACFT score calculator: enter your 6 event results plus age and gender to estimate your Army Combat Fitness Test score (0–600), with a 60-point pass/fail gate per event. Simplified from published standards.
Acid Base Calculator — pH of Strong & Weak Acids/Bases, Salts, Titration — nrtechstudio
Free acid base calculator: pH of strong and weak acids/bases from Ka/Kb, salt hydrolysis pH, strong acid–strong base titration curve and equivalence p
Acreage Calculator — Land Area in Acres, Hectares & Sq Ft
Free acreage calculator: compute land area in acres from length × width, triangle, trapezoid, circle, or irregular 4-sided lots. Results in acres, hectares, sq ft, sq m, and perimeter.
Acres Per Hour Calculator — Field Work Rate (Spraying, Mowing, Tilling) | nrtechstudio.com
Free acres per hour calculator: enter implement width, speed and field efficiency to get acres/hour and hectares/hour, with reverse solver, time planner, typical speed tables and worked examples. 100% client-side.
Acres to Hectares Converter — Free Two-Way acres ↔ hectares Tool
Free acres to hectares converter with exact constants (1 acre = 0.40468564224 ha). Convert acres ↔ hectares plus sq ft, sq m, sq km, quick conversion table and the formula.
Actual Cash Value Calculator — ACV Formula for Cars & Property (Free)
Free actual cash value calculator: estimate ACV for your car or property with transparent straight-line and declining-balance depreciation, mileage and condition adjustments, deductible math, and ACV vs replacement cost comparison.
Add Business Days Calculator
Free add business days calculator — add working days to any date with custom weekends, US federal holidays, skipped-date audit trail, and Excel WORKDAY formula generator.
Add Text to Each Line Online – Text Line Tools
Online text tool to add prefix/suffix to each line, whatsapp conversation generator, and AI tools examples reference.
Add Times Calculator - Sum Hours, Minutes and Seconds Online
Free add times calculator: add and subtract hours, minutes and seconds in a list, get the total, average, decimal hours and minutes. Perfect for timesheets and payroll.
Add Years to Date Calculator — Future Date Adder (Free)
Free add years to date calculator: add years, months, and days to any date. Leap-year safe future date calculator — Feb 29 rolls to Feb 28, with day of week, ISO week number, quarter, and day of year. Subtract years too. 100% private, runs in your browser.
Adding Machine Calculator — Virtual Paper Tape & Running Total
Free online adding machine calculator with a virtual paper tape: add and subtract numbers in sequence, see the running subtotal, edit or delete any tape line, print or copy the tape. 100% client-side, private.
Adjusted Age Calculator for Premature Babies
Free adjusted age (corrected age) calculator for premature babies. Enter birth date and gestational age at birth to get chronological vs adjusted age in years/months/days, total weeks, and the catch-up date.
Adjusted Weight Calculator — IBW, AdjBW & Amputation Weight Estimates
Educational adjusted body weight calculator: compute IBW (Devine formula), AdjBW = IBW + 0.4×(actual−IBW) for drug dosing in obesity, and pre-amputation weight estimates from body-segment frac
Adrenal Washout (CT) Calculator — Calculate Absolute & Relative Washout
Free adrenal washout calculator: compute absolute washout and relative washout from CT HU values (unenhanced, portal venous, delayed 15 min) for adrenal lesion evaluation. A radiology education tool.
ADU Cost Lab — How Much Does an ADU Cost? Build, Permit & ROI Calculator
Free interactive ADU cost lab: build-cost estimator for detached, attached, garage conversion, basement & JADU types; prefab vs stick-built comparator; ADU permit fees for all 50 states + DC; rental income ROI & payback calculator; ADU vs home-addition comparison; HELOC & construction-loan financing estimator; site-work cost adders. 100% client-side.
AES Encryptor — AES-256 Text File Encryption Online (Free, GCM)
Free online AES-256 encryptor. Encrypt text and files with AES-256-GCM (authenticated) or OpenSSL-compatible AES-256-CBC, PBKDF2 key derivation, random salt per file. 100% client-side — nothing ever leaves your browser.
AFFO Calculator — Adjusted Funds From Operations (REIT)
Free AFFO calculator: compute Adjusted Funds From Operations for any REIT — full FFO reconciliation, maintenance capex, straight-line rent adjustment, AFFO per share, P/AFFO, AFFO yield and payout ratio. 100% client-side, no signup.
AFT Calculator — Army Fitness Test Score Calculator (2025 Standards) | nrtechstudio.com
Free Army Fitness Test (AFT) calculator: score all 5 events (deadlift, hand-release push-up, sprint-drag-carry, plank, 2-mile run) against the officia
Age-Adjusted D-Dimer Calculator — Cutoff by Age (FEU & DDU)
Free age-adjusted D-dimer cutoff calculator: age × 10 µg/L FEU for patients over 50, 500 µg/L at 50 or below. Converts µg/L, ng/mL, mg/L and FEU/DDU. 100% client-side educational tool.
Ah to kWh Calculator — Convert Battery Amp-Hours to Kilowatt-Hours
Free Ah to kWh calculator: convert battery amp-hours to kilowatt-hours (kWh = Ah × V ÷ 1000). Also converts kWh back to Ah, handles mAh, battery presets, series/parallel banks, and estimates device runtime.
AI Water Footprint Calculator — Per-Query Range Estimate
Estimate your daily AI usage water footprint (mL–L range) from verified literature: the UC Riverside 'Making AI Less Thirsty' study, Microsoft sustainability reports, and IEA data. Always shown as a range, not a single figure.
Air Compressor Size Calculator — CFM, Tank, HP & Breaker Sizer | nrtechstudio.com
Size your air compressor right: match CFM to air tools, pick tank gallons, single vs two-stage, plus breaker and wire size. Free, 100% in-browser tool.
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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.