Science Calculators

Ohm's Law, Force, Pressure, Density and Resistor Colour Code Calculators

Six calculators for the formulas that turn up in school physics, workshop electronics and practical engineering. Each one solves its equation for whichever quantity you leave blank, accepts the units you actually have, shows the answer in the units everyone else uses, and adds a reference table. Everything runs in the browser.

Every Science tool

Battery Life Calculator

How long a battery lasts from capacity and load, allowing for efficiency.

Mach Number Calculator

Convert speed to Mach and back using the speed of sound at your altitude.

Resistor Colour Code Calculator

Resistor value and tolerance from 4 or 5 colour bands, with the code table.

Ohm's law: V, I, R and P

The Ohm's law calculator takes any two of voltage, current, resistance and power and returns the other two, with the results scaled into millivolts, kilohms or milliwatts as appropriate. It is the first stop for LED series resistors, heater currents, fuse ratings and working out whether a resistor will survive the power it dissipates. The formula wheel in the table shows all twelve rearrangements.

Force from mass and acceleration

The force calculator solves F = m × a in kilograms, grams, pounds or tonnes and in metres per second squared, feet per second squared or multiples of g, with force reported in newtons, kilonewtons, pounds-force and kilograms-force. Leave mass blank to find what a given force will accelerate, or acceleration blank to find how hard a force pushes a mass. The table shows the weight of the same mass on other planets.

Pressure from force and area

The pressure calculator divides force by area and lists the result in pascals, kilopascals, bar, psi, atmospheres, megapascals and mmHg at once, so a hydraulic or footing calculation reads immediately in whichever unit the datasheet uses. It rearranges to find the force a pressure exerts on a piston or window, or the area needed to keep a load within a bearing pressure. Reference pressures from a car tyre to the Mariana Trench give a sense of scale.

Density, mass and volume

The density calculator works ρ = m ÷ V in any direction, with mass in kilograms, grams, pounds or tonnes and volume in litres, cubic metres, millilitres, cubic feet or US gallons. It reports specific gravity and whether the material floats, and the table of common material densities lets you find the weight of a slab of concrete or a sheet of steel without looking anything up.

Resistor colour codes

The resistor colour code calculator turns the bands on a four- or five-band resistor into a value, tolerance and guaranteed range, and reports whether the combination is a standard E24 value, which catches most reversed or misread resistors. The full colour code table sits under the result for reading resistors by eye.

Battery life

The battery life calculator estimates run time from capacity in mAh, Ah or Wh and load in milliamps, amps or watts, with fields for converter efficiency and the reserve you will not use, so the answer is realistic rather than a bare capacity-over-current figure. It shows usable capacity in Wh, the discharge C-rate, and run times at a quarter, half, double and four times the load. Together with the battery sizing calculator it covers both directions of the problem: how long a battery lasts, and how big a battery a load needs.