All Calculators

Calculate the cutoff frequency and time constant of a first-order RC high-pass filter from its resistance and capacitance — f_c = 1 / (2π × R × C).

Calculate the cutoff frequency and time constant of a first-order RC low-pass filter from its resistance and capacitance — f_c = 1 / (2π × R × C).

Calculate the time constant of an RC circuit — τ = R × C — the time it takes to charge to ~63 % or discharge to ~37 % of the final voltage.

Estimate how long a text takes to read from its word count and your reading speed, shown in minutes and seconds.

Work out what a run of reinforcing bar weighs — for a bar schedule, a delivery note or a lift.

Calculate the area, perimeter, and diagonal of a rectangle from its length and width — area = L×W, perimeter = 2(L+W), diagonal = √(L²+W²).

Calculate the volume, surface area, and space diagonal of a rectangular prism (box) from its length, width, and height — volume = l×w×h, surface area = 2(lw+lh+wh), diagonal = √(l²+w²+h²).

Calculate the redshift z = (λ_observed − λ_rest) / λ_rest of a spectral line and the low-redshift recession velocity of a galaxy from its wavelengths.

Calculate the refractive index (n = c / v) of a medium from the speed of light within it, using the exact speed of light in vacuum.

Calculate the volume and surface area of a regular dodecahedron from its edge length — volume = ((15+7√5)/4)·a³, surface area = 3√(25+10√5)·a².

Calculate the volume and surface area of a regular icosahedron from its edge length — volume = (5(3+√5)/12)·a³, surface area = 5√3·a².

Calculate the volume and surface area of a regular octahedron from its edge length — volume = (√2/3)·a³, surface area = 2√3·a².

Calculate the area, perimeter, and apothem of a regular polygon from its number of sides and side length — area = ½ × perimeter × apothem, apothem = s/(2·tan(π/n)).

Calculate the volume, surface area, and height of a regular tetrahedron from its edge length — volume = a³/(6√2), surface area = √3·a², height = a·√(2/3).

Calculate the combined resistance of two resistors in parallel using the product-over-sum rule — Rp = (R1 × R2) ÷ (R1 + R2).

Calculate the total resistance of two resistors in series — they simply add: R = R1 + R2.

Calculate the resonant frequency of an LC circuit from its inductance and capacitance — f = 1 ÷ (2π√(L × C)).

Calculate the magnitude of the resultant of two forces acting at an angle using R = √(F1² + F2² + 2·F1·F2·cosθ).

Calculate a room's Sabine reverberation time (RT60) and total absorption from its volume, surface area, and average absorption coefficient — RT60 = 0.161·V/A, A = S·α.

Find the original value before a percentage increase or decrease, or work out what number a value is a given percentage of.

Calculate the Reynolds number (Re = ρvL/μ) from fluid density, velocity, characteristic length, and dynamic viscosity, and see whether the flow is laminar or turbulent.

Calculate the area, side length, and perimeter of a rhombus from its two diagonals — area = (d1 × d2) ÷ 2.

Calculate the hypotenuse, area, perimeter, and acute angles of a right triangle from its two legs — hypotenuse = √(a²+b²), area = ½ab, angles via atan.

Convert a ring's inner diameter in millimetres to US and EU/ISO ring sizes, with the inner circumference shown alongside.

Calculate the time constant of an RL (resistor–inductor) circuit from its inductance and resistance — τ = L / R — plus the time to reach steady state.

Calculate the RMS voltage (V_rms = V_peak / √2) and peak-to-peak voltage of a sine wave from its peak voltage (amplitude).

Calculate the road or slope grade as a percentage ((rise / run) × 100) and the slope angle in degrees from a vertical rise and a horizontal run.

Calculate the change in velocity (Δv = ve · ln(m0/mf)) of a rocket from its exhaust velocity and its wet and dry mass using the Tsiolkovsky rocket equation.

Convert any whole number from 1 to 3999 into its standard Roman numeral, using the subtractive notation (IV, IX, XL, XC, CD, CM).

Solve for the unknown value in a proportion using the rule of three (Dreisatz), with support for both direct and inverse relationships.

Calculate the wavelength of a hydrogen spectral line with the Rydberg equation (1/λ = R·(1/n1² − 1/n2²)) from the two principal quantum numbers.

Calculate your total SAT score from the Math and Reading & Writing (EBRW) section scores and see the national percentile rank.

Convert a measured model or map length into the real-world length for any 1:N scale, plus the reverse scaled-down length.

Calculate the Schwarzschild radius (event horizon) r_s = 2GM/c² of any mass in metres and kilometres — the radius at which it would become a black hole.

Convert any decimal number into scientific notation — a coefficient between 1 and 10 multiplied by a power of ten — and read off the mantissa and exponent.

Calculate the physical width and height of a screen from its diagonal size and aspect ratio (16:9, 4:3, 21:9) in the same unit as the diagonal.

Calculate the area, arc length, and chord of a circular sector from its radius and central angle — area = (θ/360)·πr², arc length = (θ/360)·2πr.

Calculate the area, perimeter, arc length, and diameter of a semicircle from its radius — area = ½πr², perimeter = πr + 2r, arc = πr.

Calculate the combined capacitance of two capacitors in series using the product-over-sum rule — C = (C1 × C2) ÷ (C1 + C2).

Convert shoe sizes between EU, UK, US (Men), US (Women), and foot length in centimetres — instantly, using the documented foot-length method.

Round any number to a chosen count of significant figures, with a worked explanation of how the rounding place is found.

Calculate the skin depth of an AC current in a conductor from the frequency, resistivity, and relative permeability — δ = √(ρ / (π × f × µ₀ × µr)).

Calculate the slope (gradient) and y-intercept of the line through two points — slope = (y2 − y1) ÷ (x2 − x1) and y = mx + b.

Calculate the angle of refraction with Snell's law (n1·sin θ1 = n2·sin θ2) from the two refractive indices and the angle of incidence.

Calculate the daily energy output (kWh) of a solar panel or array from its wattage, the site's peak sun hours, and a performance ratio.

Calculate the stock volume needed and the diluent to add using C₁V₁ = C₂V₂ when diluting a solution to a target concentration and final volume.

Calculate the sound intensity level in decibels (L = 10 · log₁₀(I/I₀), with I₀ = 1e-12 W/m²) from a measured sound intensity in watts per square metre.

Calculate how a point source's sound pressure level drops with distance in a free field — L2 = L1 − 20·log10(d2/d1). Doubling the distance lowers the level by about 6 dB.

Calculate the specific gravity (relative density) of a substance from its density and a reference density such as water at 4 °C (1000 kg/m³).

Calculate the specific heat capacity c = Q / (m·ΔT) in J/(kg·K) from the heat energy added, the mass, and the temperature change of a sample.