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.
Flexbox Builder — Visual CSS Flex Layout Generator
Free online flexbox builder: design CSS flex layouts visually with live preview, per-item controls, layout presets, and copy-paste CSS output. 100% client-side.
Flight Emissions Calculator — Estimate Your Flight's CO2
Estimate CO2 emissions for any flight: enter origin and destination (or distance), cabin class, and round trip to get kg CO2 with car, tree, and home-electricity equivalents plus an offset cost estima
Flight Radiation Exposure Calculator — Cosmic Ray Dose per Flight (μSv) — nrtechstudio.com
Free flight radiation calculator: estimate cosmic radiation exposure per flight from duration, cruising altitude and latitude zone. Results as an honest range (μSv and mSv) with chest X-ray and annual background comparisons. Educational estimates only — not medical advice.
Floor Lamp Size Calculator — Height, Arc, Torchiere & Shade Sizer | nrtechstudio.com
How tall should a floor lamp be? Free floor lamp size calculator: ceiling-fit height, arc lamp reach, torchiere & reading lamp sizer, shade proportion
Flooring Calculator
Flooring calculator: boxes, waste by pattern, stagger planner, underlayment, trim and install cost for hardwood, laminate, engineered and LVP.
Florida Overtime Pay Calculator — 1.5× for Hours Over 40
Calculate Florida overtime pay: 1.5× the regular rate for hours over 40/week (federal FLSA rules). Hourly mode, salary→hourly conversion, scenario comparison, and FAQ. Free.
Flow Rate Calculator - Q = A·v Solver, Unit Converter, Mass Flow & Tank Fill Time
Free flow rate calculator: solve Q = A·v three ways (flow rate, velocity, or diameter), convert between m³/s, L/s, L/min, GPM, CFM and cfs, compute mass flow ṁ = ρ·Q, and estimate tank fill time t = V
Fluid Ounces to Pounds Converter - fl oz to lb Calculator
Convert fluid ounces to pounds with this free fl oz to lb calculator. Pick water, milk, oil, honey, or enter a custom density. Includes conversion tables, the fl oz to lb formula, and answers to common questions.
Flyback Converter Calculator — Vout, Duty Cycle & Turns Ratio Solver
Flyback DC-DC converter calculator: compute Vout, duty cycle, or the N2/N1 turns ratio from the ideal CCM formula Vout = Vin·(N2/N1)·D/(1−D). Includes CCM/DCM boundary check and MOSFET & diode stress estimates.
Flywheel Energy Storage Calculator - E = ½Iω², RPM Solver & Material Limit
Free flywheel energy storage calculator: compute stored energy E = ½Iω² for solid disc or rim rotors, solve 3 ways (energy, RPM, or mass), and check the hoop-stress material limit with tip speed. 100%
Font Pairing Generator — Google Font Combinations
Free font pairing generator: curated Google Font combinations by style, live heading and body previews, and copy-paste embed code plus CSS.
Foot for Meter Converter
Interactive foot for meter and meter to foot calculator, feet inches to meters centimeters, human height converter, and precision conversion formulas.
Force Converter
Free force converter: convert newtons, pound-force, kilogram-force, dynes, kilonewtons, poundals, ounce-force and kips. Two-way live conversion, all-units table, batch mode, exact formulas. 100% client-side.
FormData to JSON Converter
Convert URL-encoded form data, multipart/form-data, query strings, and HTML forms into structured JSON objects.
Formula Radius of Circle – Diameter & Area Calculator
Formula radius of circle, diameter of a circle formula, circular diameter formula, area of circle equation diameter, how to work out area of a circle using diameter, what is the formula to find diameter of a circle, equation to find the diameter of a circle, formula for calculating diameter of a circle, circle diameter to area, how to find the dimensions of a circle, diameter area calculator.
FX Forward Premium & Discount Calculator — nrtechstudio
Calculate FX forward premium/discount from spot & forward rates, 360/365 annualization, forward points (pips), covered interest parity (CIP), and compare two scenarios. Educational estimates.
Interest Rate Forward Rate Calculator — Spot, Bootstrap & FRA
Interest rate forward rate calculator: compute f(t1,t2) from the spot curve, bootstrap inter-period forwards, and simulate FRA payoffs. Free, 100% in the browser.
Fountain Pen Ink Capacity Calculator — Pages per Fill & Bottle Life (Free)
Free fountain pen ink capacity planner: filling-system database (cartridge, converter, piston, vacuum, eyedropper), pages-per-fill estimator, bottle-life calculator using Viseguy's Law, personal words-per-ml calibration, and 23 popular pens. 100% client-side.
Fountain Pen Nib Size Converter: Brand-to-Brand Chart, mm Widths & Line Renderer
Free interactive fountain pen nib size converter: convert nib grades brand-to-brand (Japanese F ≈ Western EF), browse curated mm line-width charts for 12 brands, render true-scale line widths, and decode every nib grade. No sign-up, 100% client-side.
Foyer Size Calculator — How Big Should an Entryway Be?
Free foyer size calculator: plan entryway width, door-swing clearance, traffic path, rug size, lighting hang height, coat storage, and bench depth.
Fraction To Dec
Convert fractions to decimal values.
Fraction to Percent Converter (with Steps) — nrtechstudio
Free fraction to percent calculator with show-your-work steps. Convert fractions to percents and percents to simplified fractions, including mixed numbers. Repeating decimals flagged honestly. 100% client-side — your data never leaves your browser.
Frailty Index Calculator (Rockwood 40-Item) — Deficit Accumulation Score
Free frailty index calculator based on the Rockwood deficit-accumulation model. Answer 40 items across 4 domains, get your frailty score, screening category (fit / pre-frail / frail), and a per-domain breakdown — with context for surgery planning. Educational screening aid, not medical advice.
Framingham Risk Calculator — 10-Year CVD, CHD & Stroke Score
Free Framingham risk calculator: 10-year General CVD risk (D'Agostino 2008), hard CHD risk (ATP III) and stroke risk (Framingham Stroke Risk Profile, 1991) in one tool — with points breakdown, risk categories and heart age. 100% in-browser. Educational estimate, not medical advice.
Tool - Free Billable Hours Calculator
Interactive weekly work hours timesheet, employee hours tracker, invoice rate calculator, and breakdown of how many hours in a week.
FCFE Calculator — Free Cash Flow to Equity for Shareholders
Calculate Free Cash Flow to Equity (FCFE) from FCFF or from operating cash flow (CFO), with formulas, verified examples, Gordon valuation, and FAQ.
FCFF (Free Cash Flow to Firm) Calculator — Calculate Company Free Cash Flow
Free FCFF calculator: compute free cash flow to firm from operating cash flow (CFO) or EBIT, with an FCFF-to-FCFE reconciliation bridge. Educational estimates, 100% runs in the browser.
Free Cash Flow (FCF) Calculator — Calculate Free Cash Flow
Free free cash flow (FCF) calculator: compute FCF = operating cash flow − capital expenditure, FCF from net income (indirect method), FCF margin, FCF yield, and compare two companies.
Free-Fall with Air Resistance Calculator — Terminal Velocity & v(t)
Compute terminal velocity, fall speed and distance as a function of time WITH air drag (v(t)=v_t·tanh(gt/v_t)), plus comparison vs vacuum free fall. Free, 100% client-side.
Free Fall Distance Calculator — Distance from Time & Time from Distance
Free fall distance calculator: solve distance from fall time or fall time from distance. Metric + imperial units, Moon/Mars/Jupiter gravity presets, impact velocity, and a 1–10 second reference table. Free, no sign-up, runs 100% in your browser.
Free Fall Velocity Calculator — v from Time & Height, Terminal Velocity
Free fall velocity calculator: solve v from fall time (v = g×t) or height (v = √(2gh)), plus inverse solvers, kinetic energy, terminal velocity estimator, planetary gravity, and a free-fall speed chart. 100% client-side.
Free Space Path Loss (FSPL) Calculator — 3-Way Solver
Free free space path loss (FSPL) calculator: compute FSPL from distance & frequency, or find distance / frequency from FSPL. Includes a popular-bands table and link budget context. 100% in the browser.
Freelance Rate Calculator — Hourly, Day Rate, IR35 & Contractor Suite
Free freelance rate calculator suite: salary-to-hourly rate with overhead & utilization, day-rate contractor mode, UK IR35 inside-vs-outside take-home, contract-vs-permanent comparator, and US/UK/DE/IN tax presets. 100% client-side.
Freight Class Calculator — Density-Based NMFC Class (2025 Scale)
Free freight class calculator: enter weight and box dimensions to get density (lb/ft³) and the NMFC freight class on the current 2025 density scale, plus the legacy 2021 reference scale.
Freq Conv
Convert Hz, kHz, MHz, GHz, and wavelength to frequency.
Frequency Bandwidth Calculator — BW, Q Factor & Fractional BW
Compute frequency bandwidth (BW = f_H − f_L), center frequency f_c, fractional bandwidth, Q factor, and octave conversion. Two-way solver + verified WiFi 20 MHz example. Free, 100% client-side.
Frequency Converter — Hz, kHz, MHz, GHz, RPM, rad/s & Wave Calculator | nrtechstudio
Free frequency converter: Hz, kHz, MHz, GHz, THz, mHz, rpm, rad/s, deg/s two-way conversion, plus period, wavelength (vacuum/air/water/fiber/sound), angular frequency, motor sync speed, Nyquist & aliasing, and a radio-band finder. 100% client-side — data never leaves your browser.
Light Frequency Calculator — f = c/λ, Spectrum Colors & EM Bands
Free light frequency calculator: compute f = c/λ or λ = c/f, see spectrum colors (red–violet), EM spectrum bands, photon energy E = hf, and wavenumber.
Fresh Frozen Plasma Dose Calculator (Human & Dog) | nrtechstudio.com
Free fresh frozen plasma (FFP) dose calculator: weight-based dosing for humans (10-15 mL/kg) and dogs (6-20 mL/kg), units needed, infusion time. Educa
Fresh to Dry Herb Conversion Calculator — nrtechstudio.com
Convert fresh herbs to dried herbs and back. Per-herb ratios (3:1 general, 2:1 for basil & parsley), tsp/tbsp/cup/grams/ounces, quick conversion chart, worked examples.
Fresnel Zone Calculator — R1, R2, R3, 60% Clearance & Distance Solver
Free Fresnel zone calculator: compute Fresnel zone radii 1, 2, 3 (R_n = √(n·λ·d₁·d₂/(d₁+d₂))), check 60% clearance for radio links, and a maximum distance solver. 100% client-side.
Darcy Friction Factor Calculator - Colebrook Solver & Moody Chart
Free Darcy friction factor calculator: solve f from Reynolds number and relative roughness with the iterated Colebrook-White equation, compare Haaland and Swamee-Jain approximations, reverse-solve Re
Fire Hose Friction Loss Calculator — FL, PDP & Nozzle Pressure | nrtechstudio.com
Free fire hose friction loss calculator. Enter flow (GPM), hose length and diameter to get FL = C(Q/100)²(L/100), pump discharge pressure (PDP = nozzle pressure + friction loss + elevation + appliance loss), FL per 100 ft, and nozzle reaction. Imperial + metric, 100% in-browser.
Froude Number (Fr) Calculator — 3-Way Solver + Regime Classification
Compute the Froude number Fr = v/√(g·L): 3-way solver (Fr, velocity, characteristic length), subcritical/critical/supercritical classification, ship (LWL) & open-channel context. Free, 100% client-side.
Tool - Ft to Cm Converter
High-precision Feet to Centimeters (ft to cm) converter and feet and centimeter engineering calculator with instant bidirectional calculation, visual height comparison, and conversion tables.
Ft to M Converter: Feet to Meters and Meters to Feet
Free ft to m converter: convert feet to meters and meters to feet instantly. How many meters are in a foot? 1 ft = 0.3048 m exactly. Includes ft to meters chart, height, construction, and aviation examples.
Fuel Distance Calculator — How Far Can You Go on a Tank? | nrtechstudio.com
Free fuel distance calculator: enter fuel amount and economy to get maximum driving range in miles or km. Tank presets, reserve-fuel warning, one-way vs round-trip checker, simple EV range mode, MPG to L/100km converter.
Fuel Economy Converter: MPG to L/100km Calculator
Free fuel economy converter: convert MPG (US and UK) to L/100km and km/L, calculate trip fuel cost, and compare car fuel efficiency side by side.
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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.