The calculating house · 3718 instruments in service
Measurement,
to the decimal.
Every instrument here shows the formula it used, the working behind the answer, and the references it stands on. No guessed figures, no hidden arithmetic — and each result is computed twice, in two independent implementations, before it ships.
Type a problem in plain text — d/dx x^2 sin(x), x^2-5x+6=0, int_0^pi sin(x) dx. A computer-algebra engine solves it and shows the working; the answer is checked, not guessed.
Most Used
3718 built, tested, and on the benchMortgage Calculator
Monthly payment, total interest, and the full amortisation table — drawn year by year.
In service MI-02-118 · FinanceCompound Interest Calculator
Enter a principal, a nominal annual rate, a compounding frequency and a term to get the final balance and the interest alone.
In service MI-02-318 · FinanceLoan Calculator
Enter any loan amount, rate, and term to see the monthly payment plus the total interest it actually costs over the full life of the loan.
In service MI-14-204 · OtherTip Calculator
Work out how much to tip and what the total comes to, from your bill amount and a tip percentage — for restaurants, bars, cafes and takeout.
In service MI-02-172 · FinanceDiscount Calculator
Give a ticket price and a percent off; read the sale price and the exact saving, with the multiplication shown and the two figures adding back up.
In service MI-02-514 · FinanceSales Tax Calculator
Enter a pre-tax price and a combined rate; read the tax the register adds and the total you pay, with the checkout multiplier shown.
In service MI-04-001 · HealthBMI Calculator
Body-mass index on a graduated scale, with the healthy weight range for your height.
In service MI-04-084 · HealthBMR Calculator (Basal Metabolic Rate, Mifflin St Jeor Equation)
The Mifflin-St Jeor equation for resting calories: sex, weight, height, and age in — kcal per day out, with every term of the arithmetic shown.
In service MI-04-098 · HealthCalorie Calculator
Find a daily calorie target from weight, height, age, sex, activity level, and goal — resting rate scaled by activity, then adjusted for weight loss, maintenance, or gain.
In service MI-04-086 · HealthBody Fat Calculator
Estimate body fat percentage from waist, neck, hip and height with the US Navy circumference equations. Separate male and female modes, working shown.
In service MI-04-223 · HealthIdeal Weight Calculator
The Devine equation worked out in full: a base figure at five feet plus 2.3 kg for every inch of height above it, read in kg, pounds or stone.
In service MI-06-001 · Everyday lifeAge Calculator
Your exact age in years, months and days — plus total days and your next birthday.
In service MI-01-001 · MathematicsPercentage Calculator
Three ways round: X% of Y, X as a percent of Y, and percent change between two figures.
In service MI-01-409 · MathematicsPercentage Increase Calculator
Measures how much larger a value has grown, relative to where it started — (new − old) ⁄ old × 100, always zero or positive, working shown.
In service MI-01-463 · MathematicsQuadratic Formula Calculator
Solve any quadratic ax² + bx + c = 0 for both roots at once from its three coefficients, with the ± split shown as two separate values.
In service MI-01-238 · MathematicsFraction Calculator
Perform any basic operation on two fractions and get the result already simplified to lowest terms, with an operation selector.
In service MI-01-048 · MathematicsAverage Calculator
Type a list of numbers and read the arithmetic mean, the sum, and the count — formula shown, every step of the division written out.
In service MI-01-558 · MathematicsSlope Calculator
Enter two points and read the slope as rise over run, plus the line's angle of inclination in degrees via the arctangent. Working shown.
In service MI-07-174 · StatisticsStandard Deviation Calculator
Calculate standard deviation from any data set — both the sample (s) and population (σ) forms, computed side by side so you can compare them directly.
In service MI-01-460 · MathematicsPythagorean Theorem Calculator
Two sides of a right triangle in, the third out: c = √(a² + b²) for the hypotenuse, b = √(c² − a²) for a missing leg. Formula and working shown.
In service MI-01-631 · MathematicsTriangle Area Calculator
Enter the base and the perpendicular height, read the area — in cm, m, or ft — with the half-rectangle formula A = b·h/2 shown and explained.
In service MI-03-327 · PhysicsOhm's Law Calculator
Current in amperes, resistance in ohms, voltage out — V = I·R, with working shown and prefixed units handled for you.
In service MI-03-500 · PhysicsVelocity Calculator
Three-way solver for v = d ⁄ t: average speed from distance and time, distance from pace, or how long a journey takes — units handled for you.
In service MI-03-123 · PhysicsDensity Calculator
Mass in, volume in, density out in kg/m³. Water sits near 1000 kg/m³ — see where your material lands, with the formula and a worked example shown.
In serviceThe Card Index
14 series · 3,900 instruments catalogued- MI-01 Mathematics Geometry, algebra, sequences and number theory — worked, not just answered. 682 of 682
- MI-02 Finance Payments, interest, tax and returns, itemised to the cent. 609 of 609
- MI-03 Physics Motion, energy, waves and fields with every unit handled. 542 of 542
- MI-04 Health Body metrics and clinical formulas — instruments, not diagnoses. 388 of 439
- MI-05 Conversion Between SI and imperial, exactly, with the factor shown. 313 of 326
- MI-06 Everyday life The arithmetic of ordinary days: fuel, discounts, time. 257 of 288
- MI-07 Statistics Paste your data; get the distribution drawn properly. 179 of 195
- MI-08 Construction Materials, volumes and coverage measured before you buy. 155 of 159
- MI-09 Biology From cell counts to field ecology, quantified. 74 of 111
- MI-10 Chemistry Moles, molarity and mixtures balanced to the decimal. 103 of 108
- MI-11 Sports Pace, power and performance targets computed honestly. 104 of 111
- MI-12 Food Recipe scaling, nutrition and kitchen measures. 70 of 72
- MI-13 Ecology Footprints and flows for the world outside the window. 31 of 34
- MI-14 Other Instruments that refuse to be filed anywhere else. 211 of 224
How SolveTutor Works
The short versionThe formula is shown
Every instrument prints the equation it used and substitutes your numbers into it, step by step. You can check our arithmetic — and learn the method while you do.
Verified twice
Each formula exists in two independent implementations that must agree to twelve decimal places, plus cited test cases. A disagreement stops the build.
Nothing is invented
When a figure is undefined — dividing by zero, an impossible input — the readout blanks and says why. It never fills the gap with a plausible-looking number.