Construction, Carpentry & Concrete 8 calculators
- Rafter Birdsmouth & HAP CalculatorIRC 2021 rafter notch limitsThe birdsmouth is the notch that lets a sloping rafter sit flat on a level top plate. Get it wrong and you either lose bearing…
- Rafter Length CalculatorIRC 2021 R802 rafter framingA common rafter is cut to a line length — the distance along its top edge from the ridge plumb cut to the heel of the…
- Rebar Spacing CalculatorACI 318-19 cover, spacing and splice provisionsGive this calculator a slab or footing plan, a bar spacing and a cover dimension and it lays out the grid: how many bars run…
- Rebar Weight Calculator (lb/ft & kg/m)ASTM A615 / A706 nominal bar massesReinforcing steel is detailed in lineal feet and bought by weight, so every rebar order needs one conversion: unit weight times…
- Retaining Wall Block CalculatorNCMA SRW design practice; IRC R404.4A segmental retaining wall is taller than it looks, because the bottom course is buried. Count only the courses you can see and…
- Roof Area CalculatorSlope-factor method; 1 roofing square = 100 ft²You can take off an entire roof from the ground. Measure the building's length and width, read the pitch off a rafter or a…
- Roof Pitch CalculatorIRC 2021 R905 slope limitsRoof pitch is written as rise in inches over a 12-inch run, but almost every calculation you need it for wants a different…
- Roof Snow Load CalculatorASCE/SEI 7-16 Chapter 7Enter the ground snow load for your site and this calculator returns the balanced design snow load on your roof, following…
Everyday Life & Household 8 calculators
- Raised Garden Bed Soil CalculatorA raised bed swallows far more soil than people expect: a single 4 ft × 8 ft bed twelve inches deep takes 32 cubic feet, which…
- Rent Split by Room Size CalculatorHybrid common-space and private-area allocationSplitting rent evenly is only fair when the bedrooms are equal, and they almost never are. This calculator charges every…
- Rental Car Total Cost CalculatorThe rate on the comparison site is the smallest part of a rental car bill. Collision waiver, a second driver, a young-driver…
- Rideshare vs Driving Cost CalculatorIRS standard mileage rateThis calculator settles the question you ask standing on the kerb: is it cheaper to book a ride or take your own car? It builds…
- Ring Size Calculator (From Finger Measurement)US ring scale (0.032 in per size); ISO 8653 circumference sizingEvery national ring-size scale is a straight line through one measurement: the inside circumference of the band. Give this…
- Road Trip Drive Time & Arrival CalculatorEnter the distance and the average speed you expect to hold and this calculator returns three numbers a route app hides from…
- Roommate Utility Bill Split CalculatorPerson-day prorationEnter one utility bill and how long each roommate was actually in the house, and this calculator hands back what each person…
- Rug Size for Room CalculatorStandard US stock rug sizesThis calculator turns a room measurement into a rug size you can actually buy. For a living room or entry it works backwards…
Real Estate & Property Investment 6 calculators
- Real Estate Commission CalculatorNegotiated brokerage commission; written agreements required for buyer representationCommission is usually the largest single cost of selling a house, and it is negotiable — there is no standard rate, and since…
- Rent Increase CalculatorCompound escalation; CPI-plus-base rent cap structureThis calculator answers the three questions a rent change raises. What is the new rent after a percentage or dollar increase?…
- Rental Property Cash Flow CalculatorProperty-level cash flow after debt serviceCash flow is what is left after the tenant pays, the property spends, and the lender is satisfied. This calculator takes it in…
- Rental Property Depreciation CalculatorMACRS GDS: 27.5-year residential / 39-year nonresidential, mid-month conventionDepreciation is the largest deduction most rental owners take and the one most often computed wrongly, because three things…
- Rental Property ROI CalculatorTotal return on invested equityA rental pays you four ways, and cash flow is only the first. This calculator adds the mortgage principal your tenant retires…
- Rental Yield Calculator (Gross & Net)Gross and net initial yield (buy-to-let convention)Rental yield is annual rent as a percentage of what the property cost you. Gross yield uses rent alone; net yield deducts voids…
Investing & Retirement 5 calculators
- Required Minimum Distribution (RMD) CalculatorIRS Publication 590-B, Uniform Lifetime TableYour required minimum distribution is one division: the balance in your traditional IRA or employer plan on 31 December of last…
- Retirement Savings Needed CalculatorPresent value of an inflation-indexed annuityThis calculator sizes the portfolio you need on the day you retire. It starts from the spending your investments actually have…
- Roth Conversion Tax CalculatorIRC §408(d)(2); 2025 IRS rate scheduleA Roth conversion is voluntary income. You choose the amount, and that choice sets the tax bill, so the only question worth…
- Roth IRA Growth CalculatorIRC §408A (Roth IRAs)A Roth IRA compounds without any annual tax drag and, once the distribution is qualified, pays out entirely free of federal…
- Rule of 72 Doubling Time CalculatorEnter a rate of return and this calculator gives you three numbers at once: the Rule of 72 shortcut you can do in your head…
Accounting & Financial Statement Analysis 4 calculators
- Retained Earnings CalculatorUS GAAP · ASC 250 & ASC 505-20Retained earnings is the running total of every dollar your company has earned and not handed out. This calculator rolls the…
- Return on Assets (ROA) CalculatorUS GAAP financial statements (SEC Reg S-X 5-02 and 5-03)Return on assets tells you how many cents of profit each dollar of assets produced. Enter net income and the total assets on…
- Return on Equity (ROE) CalculatorUS GAAP (ASC 260 income available to common; SEC Reg S-X 5-02)Return on equity is the profit a company earns on the money its owners have left in the business. Enter net income, any…
- Return on Invested Capital (ROIC) CalculatorAnalyst convention: NOPAT ÷ average invested capitalReturn on invested capital is the cleanest single test of whether a business is any good: after-tax operating profit divided by…
Calculus, Linear Algebra & Discrete Math 4 calculators
- Radius & Interval of Convergence CalculatorRatio test, root test and the Cauchy–Hadamard theoremGive this calculator the coefficient formula aₙ of a power series, its centre, and the exponent pattern, and it returns the…
- Riemann Sum Calculator (Left, Right, Midpoint)Riemann integration; composite Newton–Cotes rulesEnter a function, an interval and a number of subintervals, and this calculator builds the Riemann sum term by term: it shows…
- RREF & Gauss-Jordan CalculatorGauss-Jordan elimination with partial pivotingType a matrix one row per box and this calculator reduces it to reduced row echelon form, listing every elementary row…
- Runge-Kutta RK4 CalculatorClassical fourth-order Runge-Kutta (Kutta, 1901)Enter the right-hand side of dy/dx = f(x, y) , an initial condition, a step size and a final x , and this calculator marches…
HVAC, Refrigeration & Building Science 4 calculators
- R-Value to U-Value Converter CalculatorASHRAE Fundamentals thermal resistance conventionsR-value and U-factor are reciprocals of one another, but they are quoted in different units on either side of the Atlantic and…
- Radiant Floor Loop Length CalculatorASHRAE Standard 55 floor-temperature limit; manufacturer loop-length tablesGive this calculator a zone area, a tube spacing and the zone's heat loss, and it returns the total PEX you need to buy, how…
- Relative Humidity CalculatorASHRAE Handbook—Fundamentals, Ch. 1 (Hyland–Wexler)Enter a dry-bulb and wet-bulb reading from a sling psychrometer or a digital hygrometer and this calculator returns relative…
- Room CFM Requirement CalculatorACCA Manual D room airflowThe airflow a room needs follows from one equation: sensible load divided by 1.08 times the temperature difference between the…
Home Improvement Projects & Renovation 4 calculators
- Renovation Contingency CalculatorRisk-based contingency framework (defined on this page)A flat ten per cent contingency treats a 1910 house with plaster walls and knob-and-tube wiring the same as a 2015 house with…
- Renovation Downtime Cost CalculatorDisruption cost accountingA renovation quote covers the work. It does not cover the six weeks of takeaways while the kitchen is a shell, the storage unit…
- Renovation Equity Gain CalculatorAfter-repair value (ARV) equity identityA renovation can raise the value of your house and still leave you worse off. This calculator separates the two: it shows the…
- Roof Replacement Cost CalculatorIRC Chapter 9 (roof assemblies)Roofing is priced by the square — 100 ft² of roof surface, not of ground area — so the first thing this calculator does is…
Arithmetic, Algebra & Number Theory 3 calculators
- Ratio Simplifier CalculatorEuclid's algorithmEnter two or three terms and this calculator reduces them to the smallest whole numbers that carry the same proportion…
- Reverse Percentage CalculatorThis calculator recovers the number you started with. Give it a value that has already had a percentage applied — a sale…
- Rounding CalculatorIEEE 754-2019Pick a place — hundredths, whole numbers, nearest thousand — choose a tie-breaking rule, and this calculator rounds…
Business, Marketing & E-commerce 3 calculators
- Reorder Point CalculatorContinuous-review (s, Q) inventory modelThis calculator gives you the trigger level: the number of units at which you must place your next purchase order so that…
- ROAS Calculator (Return on Ad Spend)MASB Common Language Marketing DictionaryROAS is attributed revenue divided by ad spend, and on its own it tells you almost nothing about whether a campaign made money…
- Rule of 40 CalculatorRule of 40 (Feld, 2015)The Rule of 40 adds one number to another: your year-over-year revenue growth rate and your profit margin, both in percent. If…
Cooking, Baking & Brewing 3 calculators
- Recipe Cost Per Serving CalculatorStandard recipe costing method (AP price ÷ pack size)This calculator costs a recipe the way a chef's costing sheet does: each ingredient line is priced from the pack you actually…
- Recipe Scaling CalculatorRecipe conversion factor (RCF) method, standard culinary practiceEnter the yield your recipe was written for and the yield you need, and this calculator returns the recipe conversion factor —…
- Restaurant Prime Cost CalculatorUniform System of Accounts for Restaurants, 8th ed.Prime cost is cost of sales plus total labour, and it is the number most operators manage weekly because together those two…
Crafts, Textiles, 3D Printing & Photography 3 calculators
- Resin (SLA/MSLA) 3D Print Cost CalculatorResin printing costs are dominated by two things that pull in opposite directions: the resin itself, which scales with part…
- Resin Mold Volume & Mixing CalculatorMix ratio by weight or by volume, per the resin data sheetTwo questions decide whether a resin pour succeeds: how much to mix, and how to split it between the two components. This…
- Ring Blank Length CalculatorUS ring size scale; ISO 8653 ring sizingCut a ring blank to the inside circumference and the finished ring comes out at least a full size small. The metal on the…
Electrical Trade & Electronics 3 calculators
- RC Filter Cutoff Frequency CalculatorFirst-order RC network, −3 dB corner definitionGive this calculator a resistor and a capacitor and it returns the −3 dB corner frequency of the RC network, the time constant…
- RC Time Constant & Charge Time CalculatorFirst-order RC transient responseEnter a resistance and a capacitance and this calculator returns the time constant τ = RC , the capacitor voltage at any…
- RLC Series Impedance CalculatorAC steady-state phasor analysisEnter the resistance, inductance and capacitance of a series branch and the frequency it runs at, and this calculator returns…
Geometry & Trigonometry 3 calculators
- Rectangle Area & Perimeter CalculatorEnter any two of a rectangle's defining quantities and this calculator returns the rest: area, perimeter, diagonal, aspect…
- Rectangular Prism Volume & Surface Area CalculatorEuclidean solid geometryEnter length, width and height and this calculator returns the volume of the box, its capacity in gallons, litres, cubic…
- Right Triangle Calculator (SOHCAHTOA)A right triangle is fully determined by any two of its parts other than the two acute angles, and this calculator solves it…
Agriculture, Livestock & Landscaping 2 calculators
- Round Bale Weight CalculatorBale volume × bulk density, dry matter basisA round bale is priced by the bale and fed by the ton, and the two only line up if you know what the bale weighs. This…
- Row Spacing & In-Row Seed Spacing Calculator43,560 ft² per acre geometryPlanters are set in inches between seeds, but agronomy is written in plants per acre, and this calculator moves between the…
Automotive, Diesel & Motorsports 2 calculators
- Road Trip Fuel Cost CalculatorTrip fuel cost is three numbers multiplied together, but the one that catches people out is effective fuel economy — the MPG…
- Rocker Arm Ratio & Valve Lift CalculatorRocker lever ratio and net-lift conventionRocker arms are levers, so the lift at the valve is the lift at the cam lobe multiplied by the rocker ratio. Change the ratio…
Computing, IT, Networking & Security 2 calculators
- RAID Capacity CalculatorSNIA Common RAID Disk Data Format; IEC 80000-13 binary prefixesEnter your drive count, drive size and RAID level and this calculator returns the capacity you can actually write to — in…
- RAID IOPS & Write Penalty CalculatorSNIA storage performance terminologyAn application asking for 5,000 IOPS does not put 5,000 operations on your disks. Every small write to a parity RAID set costs…
Education, Grading & Test Scores 2 calculators
- Reading Speed (WPM & Fluency) CalculatorCurriculum-based measurement of oral reading fluencyTime a reader on a passage, count the words and the uncorrected errors, and this calculator returns the four numbers a reading…
- Reading Time CalculatorBrysbaert (2019) reading-rate meta-analysisReading time is one division — words divided by words per minute — and the only hard part is choosing an honest rate. This…
Health, Fitness & Nutrition 2 calculators
- Race Time Prediction Calculator (Riegel)Riegel endurance model (t = a·d^1.06)Enter one recent race result and this calculator predicts your finish time at any other distance, using Peter Riegel's…
- Running Pace CalculatorPace = time ÷ distancePick what you want to solve for — pace, finish time or distance — enter the other two, and this calculator returns your pace in…
Physics: Mechanics, Waves & Thermodynamics 2 calculators
- Radioactive Half-Life & Decay CalculatorExponential decay law N = N₀e^(−λt); activity in becquerel (SI)Radioactive decay is exponential: a fixed fraction of the remaining nuclei decays in each equal interval, so the same half-life…
- Reynolds Number CalculatorRe = ρvD/µ; pipe transition 2,300–4,000; flat plate transition ≈ 5×10⁵The Reynolds number compares inertial forces to viscous forces and decides, on its own, whether a flow is smooth and layered or…