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.
Bishop Score Calculator: Cervical Readiness for Induction of Labor | nrtechstudio.com
Free Bishop score calculator: score the five components (dilation, effacement, station, consistency, position) on the 0-13 scale, see the favorable/in
Biweekly Time Card Calculator & Timesheet Hours
Interactive biweekly time card calculator and timesheet hours tracker for payroll, overtime, and gross wage calculations.
Black Hole Temperature Calculator — Hawking Temperature T = ħc³/(8πGMk)
Free black hole temperature calculator: compute Hawking temperature T = ħc³/(8πGMk_B) from mass in solar masses or kg, with Schwarzschild radius and CMB comparison. Includes Sgr A*, M87*, stellar and
Black-Scholes Calculator — Option Price & Greeks (Delta, Gamma, Theta, Vega, Rho)
Free Black-Scholes option pricing calculator: European call & put prices, full Greeks (delta, gamma, theta, vega, rho), implied volatility solver, and payoff diagrams. Shows d1/d2 steps. 100% client-side.
Blackbody Radiation Calculator — Stefan-Boltzmann, Wien & Planck
Free blackbody radiation calculator: total radiated power (Stefan–Boltzmann law), peak wavelength (Wien's displacement law), and spectral radiance (Planck's law). Two-way temperature ↔ power solver, p
Bladder Volume Calculator — Estimate Bladder Volume from Ultrasound (Ellipsoid Formula)
Bladder volume calculator from ultrasound results: V = 0.52 × D1 × D2 × D3. Interpretation of post-void residual (PVR) normal/borderline/abnormal and functional capacity estimates. Educational tool, not a diagnosis.
Blended Rate Calculator — Weighted Average Interest Rate of Multiple Loans
Free blended rate calculator: the weighted-average interest rate across multiple loans. Blend mortgages, HELOCs & debts, compare vs a refinance offer, and model an 80/10/10 piggyback loan.
Block Mortar Calculator — Blocks, Mortar Bags & Site Mix Estimator
Estimate concrete block count, mortar volume, 60/80-lb premix bags, and site-mix cement, lime, and sand for a CMU block wall. Based on manufacturer coverage data.
Custom Software Development Cost Estimator
Interactive software development cost calculator, mobile app scoping estimator, and enterprise engineering architecture planner.
Blood Donation Due Date Calculator — When Can I Donate Again?
Free blood donation due date calculator: enter your last donation date and donation type (whole blood, platelets, plasma, double red cells) to find yo
Blood Volume Calculator (Nadler Formula) | nrtechstudio.com
Free blood volume calculator using the Nadler formula (sex, height, weight) with Gilcher rule-of-fives comparison, metric/imperial inputs, and blood-d
BMI Calculator for Women — BMI, Healthy Weight Range & Body Fat Estimate
Free BMI calculator designed for women. Get your BMI with WHO category, healthy weight range for your height, an estimated body fat % (Deurenberg formula), and age-aware context. 100% private — runs in your browser.
BMI Calculator — Body Mass Index (Metric & Imperial) | nrtechstudio.com
Free BMI calculator with metric & imperial units. Get your Body Mass Index, WHO weight category, visual gauge, healthy weight range for your height, BMI Prime and Ponderal Index. Private — 100% in your browser.
BMI Calculator for Men — BMI, Body Fat % & Ideal Weight
Free BMI calculator for men: computes BMI, WHO category, ideal weight range, and estimated body fat percentage (Deurenberg formula for men). 100% client-side.
Child BMI Percentile Calculator (CDC, Ages 2–20)
Free child BMI percentile calculator using the CDC BMI-for-age LMS method (ages 2–20, boys & girls). Get BMI, percentile, z-score and CDC weight-status screening category.
BMI Weight Loss Calculator — Plan Your Calorie Deficit Safely
Plan weight loss from your BMI: enter height, current weight and target weight or BMI target plus a timeframe in weeks. Get the daily calorie deficit you need, a weekly projection timeline, TDEE context, and safety flags for unsafe deficits.
BMR Calculator — Mifflin-St Jeor + TDEE
Free BMR calculator using the Mifflin-St Jeor equation (men & women) with Harris-Benedict (revised) comparison, 5 activity-level TDEE, and lose / maintain / gain calorie targets. 100% client-side, educational.
Harris-Benedict BMR Calculator: Original 1919 vs Revised 1984 Equation
Free Harris-Benedict BMR calculator showing both the original 1919 and the revised 1984 (Roza-Shizgal) equations side by side, with step-by-step breakdown, history, and Mifflin-St Jeor comparison.
Board and Batten Layout Calculator — Even Spacing, Edge Margins & Cut Marks
Free board and batten layout calculator: enter wall width, batten width and target spacing (or batten count) to get even on-center spacing, edge margins, batten center marks from the corner, total linear feet of stock, and a to-scale wall preview. 100% client-side, no signup.
Board Foot Calculator: Project Mode, Cost by Species & Reference Chart
Free board foot calculator with project mode (multi-board cut lists), reverse solver, waste & milling presets, nominal-to-actual lumber tables, an editable species price database for cost estimates, and a BF reference chart. 100% client-side.
Board Game Collection Tracker: Free Play Log, Cost-Per-Play & Shelf of Shame
Free board game collection tracker and organizer: log every play, auto-compute cost per play, track your collection's value, and shame your unplayed games. No sign-up, 100% client-side, CSV export.
Board Game Picker: What Should We Play? (Quiz + 150 Games)
Can't decide what board game to play? Take the 60-second quiz or use smart filters to get ranked recommendations from 147 curated board games — 2-player, party, family, co-op & more. Free, no sign-up.
Board Game Score Sheet & Score Calculator — Free, Printable, No Sign-Up
Free board game score sheet & score calculator: multi-player score pad with auto-totals, rankings, winner highlight, game presets (Catan-style, Ticket-to-Ride-style, Wingspan-style), printable scoresheet, free CSV export, and local save. No sign-up.
Boat Capacity Lab — USCG Boat Capacity, Weight & Max HP Calculator
Free boat capacity calculator suite: USCG persons capacity (L×W/15), max weight capacity, federal max horsepower (33 CFR 183.53), ABYC H-35 pontoon worksheet, electric outboard sizing, and outboard shaft-length guide. 100% client-side.
Boat Loan Calculator — Monthly Payment, Amortization & Ownership Costs
Free boat loan calculator: monthly payment, down payment (10-20%), 60-240 month terms, marine survey & fees, trade-in, full amortization schedule with CSV export, and total ownership costs. 100% client-side.
Bocce Court Size Calculator — Dimensions, Materials & Cost Planner
Plan a bocce court: official 13x91 ft dimensions, surface and base material estimator, timber takeoff, drainage planner, yard fit checker, DIY vs pro cost. 100% client-side.
BODE Index Calculator — COPD Prognosis Score
BODE Index (Body mass, Obstruction, Dyspnea, Exercise) 0–10 calculator for COPD based on Celli et al. 2004. Compute score + quartile free.
Body Fat Calculator — US Navy, Skinfold & BMI Methods | nrtechstudio.com
Free body fat percentage calculator with 3 methods side-by-side: US Navy tape method, Jackson-Pollock 3-site skinfold and BMI-based estimate. See your ACE category, fat vs lean mass, and how to measure.
Body Frame Size Calculator — Small, Medium or Large Frame (Wrist Method)
Free body frame size calculator: enter your height and wrist circumference to find whether you have a small, medium, or large body frame. Classic height-vs-wrist chart for men and women, full reference table, worked examples and FAQ.
Body Surface Area (BSA) Calculator — DuBois, Mosteller, Haycock, Gehan-George, Boyd
Free body surface area (BSA) calculator: compute BSA in m² with DuBois, Mosteller, Haycock, Gehan & George, and Boyd formulas side by side, plus the average and optional mg/m² dose calculation. Educational tool — not medical advice.
Body Type Calculator — Ectomorph, Mesomorph, Endomorph Scores
Free body type calculator: get your somatotype blend (ectomorph, mesomorph, endomorph) from height, weight, wrist circumference and frame size. Male and female. 100% client-side.
Body Water Percentage Calculator — Watson Formula TBW | nrtechstudio.com
Body water percentage calculator using the Watson formula (Am J Clin Nutr 1980): estimate total body water in liters and as % of body weight from age,
Bohr Model Calculator — Hydrogen Energy Levels, Radius & Spectral Lines
Free Bohr model calculator for hydrogen-like atoms: energy levels E_n, orbital radii r_n, photon wavelength/energy for electron transitions (n2→n1), Lyman/Balmer/Paschen series labels, and spectral-li
Boiler Size Calculator — BTU/hr, kW & Boiler HP by Climate Zone
Free boiler size calculator: enter floor area, climate zone, insulation, ceiling height and windows to get your heat loss and recommended boiler size in BTU/hr, kW and boiler horsepower — with fuel efficiency adjustment and an oversize short-cycling checker. 100% client-side, no signup.
Bolt Circle Calculator (BCD/PCD) — Lug Pattern, Spacing & Hole Coordinates
Free bolt circle diameter (BCD/PCD) calculator: find BCD from adjacent bolt spacing for 3/4/5/6/8-lug wheels and flanges, reverse BCD to spacing, get machining X/Y hole coordinates, and match the nearest standard bolt pattern. 100% client-side.
Bolt Torque Calculator — Metric & SAE Tightening Torque (Free)
Free bolt torque calculator: T = K·F·d for metric bolts M6–M36 (classes 8.8/10.9/12.9) and SAE bolts (Grade 5/8). K-factor presets, clamp load, and a standard torque chart.
Boltzmann Factor & Thermal Population Ratio Calculator
Calculate the Boltzmann factor exp(−ΔE/kT), the thermal population ratio N2/N1, and temperature from a measured ratio. Exact SI 2019 constants. Free, 100% client-side.
Bond Price Calculator: YTM, Current Yield, BEY, Duration & Convexity
Complete bond calculator: compute bond price, YTM (yield to maturity), current yield, BEY (bond equivalent yield), Macaulay & modified duration, and convexity — with cash flow tables and price vs yield sensitivity.
Book Signature Calculator — Imposition Maps, Planner & Binding Lab | nrtechstudio
Free bookbinding signature calculator lab: signature planner (pages per signature), folio/quarto/octavo imposition page-order maps, format size converter, paper grain advisor, sewn-vs-perfect binding decision helper, and thread & material estimator. 100% client-side.
Book Spine Width Calculator + Full Cover Wrap Suite
Free book spine width calculator with a curated paper PPI/caliper database (KDP white, cream, color + offset stocks), full cover wrap dimensions, reverse page-count solver, hardcover case & dust jacket modes, and Canva/InDesign/Word export guides. 100% client-side.
Bookshelf Size Calculator — Width, Depth, Capacity & DIY Cut List
Find the perfect bookshelf size for your book collection: width, depth, shelf spacing, capacity, weight limit and wall fit — free interactive calculat
Border Radius Generator
Build custom border radius.
CSS Border Radius & Circle Radius Generator
Free visual CSS border radius with border generator and circle radius calculator. Create buttons, rounded cards, circles, and copy clean CSS code.
Bowling Average Calculator — 10-Pin Average & League Handicap | NR Tech Studio
Free bowling average calculator: enter your 10-pin game scores to get your average, series total, high game, and league handicap (220 basis, 90% default, adjustable).
Boxing Glove Size Calculator — Hand, Weight & Oz Fit Lab
Free interactive boxing glove size lab: measure your hand circumference, match body weight to the right oz (12/14/16 oz) for bag, sparring or fight, plus kids, MMA, women's fit and hand-wrap length. No signup, works offline in your browser.
Boyle's Law Calculator — P₁V₁ = P₂V₂ Solver (Free)
Free Boyle's law calculator: solve P₁V₁ = P₂V₂ for any missing variable. Pressure in Pa, kPa, bar, psi, atm or mmHg; volume in m³, L, mL or ft³. Instant results with full unit conversions. 100% client
BPM Tap Tempo Calculator Online
Free online BPM tap tempo calculator. Find BPM by tapping. Tempo BPM finder, BPM finder tap, online beats per minute calculator, tap tempo finder, BPM counter tap, BPM calculator tap, song tempo calculator, online tap tempo tool, BPM metronome tap.
Bra Size Calculator — 5-Measurement Method, Sister Sizes & Fit Guide | nrtechstudio.com
Free bra size calculator using the modern 5-measurement method (no outdated +4 rule): band + cup in UK, US, EU & FR sizes, sister-size finder, fit troubleshooter, size converter and breast-shape style guide. 100% private, runs in your browser.
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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.