Rules of thumb, calculated

Practical calculators for everyday decisions.

58calculators implemented

15topic hubs

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Testedformula logic

ThumbCalc turns useful formulas, heuristics, and community rules of thumb into fast calculators with transparent assumptions and worked examples.

Calculator categories

Home Improvement

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Garden & Outdoors

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AI & DevOps

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Parenting

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Hobbies & Makers

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Pets

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Creators & Media

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Security & IT

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Personal Finance

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Software & QA

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Gaming

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Events & Hospitality

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Electronics & IoT

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Food & Cooking

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Lab & Science

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All calculators

AI Embedding Cost and Vector Storage Calculator

Calculate embedding API cost, raw vector size, vector DB storage, index overhead, and monthly refresh/storage cost.

Hobbies & Makers

Astrophotography Bortle Exposure Equivalency Calculator

Compare Bortle or SQM sky brightness levels and estimate equivalent integration time, sub-exposure adjustment, and SNR impact for astrophotography.

Baby Clothing and Registry Quantity Calculator

Calculate baby clothing quantities for a registry, including bodysuits, sleepers, bottoms, socks, swaddles, hats, mittens, bibs, layers, and special outfits.

Baby Formula Can Duration and Monthly Cost Calculator

Calculate formula days per can, cans per month, powder per day, and estimated monthly cost.

Backup Retention Storage Calculator

Calculate retained backup storage, full and incremental counts, and estimated monthly storage cost.

Home Improvement

Baluster and Spindle Spacing Calculator

Find baluster count, exact equal gaps, on-center spacing, first and last center marks, stair sloped spacing, and total spindles for railing sections.

Home Improvement

Baseboard and Crown Molding Piece Calculator

Calculate trim linear footage, whole stock pieces, cut allowances, waste, splices, spare length, and cost for baseboard, crown molding, shoe, or chair rail.

Hobbies & Makers

Beekeeping Sugar-Syrup Calculator

Estimate sugar and water for bee syrup by target volume or sugar on hand, including finished yield, feeder fills, and container fit.

Breast Milk Freezer Stash and Daycare Calculator

Estimate daycare bottle portions, weekly expressed milk needs, freezer-bag count, stash reserve, and freezer-stash coverage for a pumping or daycare plan.

Home Improvement

Cabinet Door Paint and Primer Calculator

Calculate cabinet paint and primer quantities from door, drawer, frame, side-panel, coat, coverage, waste, and finish-condition inputs.

Home Improvement

Caulk Tube Coverage Calculator

Calculate caulk tubes, coverage per tube, material volume, and project cost from bead dimensions.

Cell Culture Seeding and Split Ratio Calculator

Plan cell culture seeding master mixes and split-ratio passage volumes from cells/mL, viability, target cells per well or cm², overage, and vessel volume.

Chicken Coop, Run and Roost Size Calculator

Calculate coop area, run area, roost length, nest boxes, and ventilation for a backyard chicken flock.

Childcare Effective Wage Calculator

Calculate what work pays after estimated tax, childcare, commuting, subsidies, and work expenses, including break-even gross hourly wage.

Code Review Effort Estimator

Calculate code review time, reviewer-hours, sessions, and review risk from pull request size and complexity.

Garden & Outdoors

Compost C:N Ratio Blender Calculator

Calculate compost C:N ratio, moisture, green/brown balance, and correction amounts from common compost materials like leaves, grass, food scraps, cardboard, straw, and manure.

Critical Software Test Effort Estimator

Estimate test effort from functional LOC and criticality, including regression, defect retest, calendar duration, and cost.

Hobbies & Makers

Cross-Stitch Fabric and Thread Calculator

Estimate cross-stitch fabric size, margins, floss skeins, needle size, and stitching time from pattern stitches, fabric count, coverage, and colors.

Home Improvement

Curtain Fabric Yardage and Fullness Calculator

Calculate curtain face fabric, fabric widths, adjusted cut length, lining, and cost.

Database Connection Pool Sizer

Calculate recommended DB pool size per instance using Little's Law, latency, app instance count, headroom, and max connection limits.

Home Improvement

Deck Board, Joist and Screw Calculator

Calculate decking boards, joists, screws, screw boxes, and board/screw cost.

Diaper Stockpile Calculator

Plan diaper packs, wipes, and cost using age-based diaper-per-day estimates.

Hobbies & Makers

Disc Golf Disc Speed Selector

Calculate recommended disc speed, control-speed range, disc class, and stability suggestion from your max flat-ground throw distance.

Dog Calorie and Food Portion Calculator

Estimate dog kcal/day and food portions from body weight, life stage, food calories, and meals per day.

Home Improvement

Drywall Sheet, Screw and Mud Calculator

Calculate drywall sheets, net area, screws, joint compound, tape, and sheet cost for a room.

Events & Hospitality

Event Bar-Stock Planner

Calculate total drinks, beer cases, wine bottles, spirit bottles, mixers, ice, and estimated event bar cost.

Home Improvement

Fence Post Concrete Bag Calculator

Calculate concrete bags for fence posts from post count, hole size, post displacement, bag yield, and waste.

Hobbies & Makers

Film Reciprocity Failure Calculator

Calculate film reciprocity failure correction from metered exposure time, film profile, p-factor exponent, threshold, and bracketing range.

Home Improvement

Flooring Plank and Box Calculator

Calculate flooring boxes, order area, spare area, underlayment rolls, and material cost.

Gacha Pity Probability and Cost Calculator

Calculate gacha pity odds, target-copy probability, expected copies, worst-case pulls, and pull cost.

Game Server Bandwidth and Tickrate Calculator

Calculate game server bandwidth from players, tickrate, payload bytes, protocol overhead, concurrency, uptime, and headroom, including monthly egress and port tier.

Home Improvement

Gravel Pad and Shed Base Calculator

Calculate gravel cubic yards, tons, bag count, and bulk cost for a compacted pad or shed base.

Home Improvement

Gutter and Downspout Capacity Calculator

Calculate adjusted roof drainage area, peak runoff, recommended gutter size, downspout count, and spacing for residential roof drainage planning.

Hot Sauce Fermentation Brine Calculator

Calculate fermented hot sauce salt by total batch weight or water-only brine method, with spoon estimates, temperature notes, and jar headspace checks.

Hobbies & Makers

Houseplant Repotting and Soil Mix Calculator

Calculate the next pot size and soil mix ingredient volumes for tropical houseplants, aroids, succulents, orchids, ferns, and propagation.

Personal Finance

Income-Based Bill Split Calculator

Calculate each person's fair share of shared bills based on their percentage of total household income.

Electronics & IoT

IoT Solar Panel and Battery Sizer

Calculate daily Wh, required solar panel watts, battery Ah, autonomy, and existing panel/battery coverage for remote IoT nodes.

Hobbies & Makers

Knot Strength Retention Calculator

Calculate estimated knot-retained rope strength, working load, dynamic-adjusted working load, and load utilisation from rope rating and knot type.

LLM Context Window and RAG Chunk Calculator

Calculate RAG chunk count, context-window fit, max chunks that fit, and prompt token budget.

LLM Token Cost Calculator

Forecast AI API spend from token volume, request count, caching, and model pricing.

Electronics & IoT

LoRa Link Budget and Range Estimator

Calculate LoRa link budget, fade margin, theoretical free-space range, receiver sensitivity, airtime, and duty-cycle packet capacity.

Mead Fruit and Honey Gravity Calculator

Calculate honey needed for mead from batch volume, target ABV, final gravity, honey PPG, fruit weight, and fruit sugar contribution.

Hobbies & Makers

Miniature Painting Dilution and Airbrush PSI Calculator

Calculate a starting thinner ratio, drop recipe, PSI range, and spray distance for airbrushing miniatures, primers, varnishes, glazes, and terrain.

Hobbies & Makers

Mushroom Spawn-to-Substrate Ratio Calculator

Estimate mushroom spawn needed from substrate weight, species, grow method, spawn percentage, substrate moisture, container count, and biological efficiency.

Pond Pump and Filter Turnover Calculator

Calculate pond pump size, delivered flow, turnover, waterfall GPH, head-height derating, filter capacity, and monthly electricity cost for garden, goldfish, and koi ponds.

Garden & Outdoors

Rainwater Harvesting Tank Size Calculator

Calculate annual rainwater harvest, dry-spell storage need, storm capture, overflow, and recommended tank size from roof area, rainfall, efficiency, and demand.

Reptile Enclosure Heat and UVB Starter Calculator

Plan reptile heat and UVB starter settings from species profile, enclosure dimensions, room temperature, enclosure material, UVB fixture, mesh, and lamp distance.

Hobbies & Makers

Resin Print Exposure Time Scaler

Estimate a new resin exposure time from a known-good exposure and target layer height.

Software Defect Density Benchmark Calculator

Calculate predicted defects, actual defects per KLOC, escaped defects, and fix effort using software defect-density benchmarks.

Sous Vide Time-to-Core Calculator

Calculate sous vide time to heat food near bath temperature from thickness, shape, start state, and optional hold time.

SQA Budget Calculator

Calculate SQA process budget, process/training split, auditing split, monthly allocation, and SQA FTE from total project hours or budget.

SRE Error Budget Calculator

Turn an SLO percentage into downtime minutes and track budget burn rate.

Home Improvement

Staircase Rise and Run Calculator

Estimate stair risers, tread count, total run, stringer length, angle, 2R+T comfort, and basic code checks from total rise and tread depth.

Tester-to-Developer Ratio Calculator

Calculate tester FTE, manual vs automation split, developer-to-tester ratio, and process SQA staffing from developer count and project risk profile.

Home Improvement

Tile Grout Calculator

Calculate grout quantity and bags from tile size, joint width, depth, area, and waste percentage.

Creators & Media

Video Recording Storage Calculator

Calculate GB per hour, total project storage, backup storage, and recommended drive size.

Home Improvement

Wallpaper Roll Calculator with Pattern Repeat

Calculate wallpaper rolls, strips, adjusted drop length, waste, and project cost.

Hobbies & Makers

Wood Movement Predictor

Calculate across-grain wood movement, shrinkage, swelling, and recommended allowance for panels, tabletops, drawers, and doors.