All tools › Circuits
Voltage divider
The output from two resistors, the current it costs, and the nearest real pair
It runs entirely in this browser tab: the numbers you type are never uploaded, and the tool makes no network request while it works. Open your browser's network panel and try it — nothing leaves the page.
What it takes
- In (V)
- A value you supply.
- Upper resistor (Ω)
- Leave it out and the tool works it out from the others.
- Lower resistor (Ω)
- Leave it out and the tool works it out from the others.
- Out (V)
- Leave it out and the tool works it out from the others.
An example
input = 12
r1 = 10000
r2 = 4700
Settings
- Value series
- Which values you actually have. E24 is a well-stocked drawer and E12 is most of them. Choices: E24, E12.
How to use it
- Fill in the boxes above. Anything you leave blank the tool works out.
- Adjust the settings beside it until the result is what you wanted.
- Copy the result, or save it as a file. The result updates as you type.
Questions
- Can I build from this?
- Not from this alone. The cable, beam and rainwater tools each say so on their own result: they are arithmetic, and what may be built is decided by the wiring, structural and water regulations where the work is — none of which this page has read.
- Why does a tool refuse a number it could clearly calculate?
- Because several of these formulas are fits rather than laws. Wind chill is defined at 10 °C or colder in a wind over 4.8 km/h, the heat index from 27 °C up, and the barometric formula to the top of the troposphere. Outside those the arithmetic still runs and the answer means nothing, so the tool says which rather than printing it.
- Does anything here use floating point?
- No. Every figure is exact decimal arithmetic, which is why 0.1 + 0.2 is 0.3 here and a unit conversion comes back to where it started. The one place a ceiling exists — how many digits an exponent may carry — is stated rather than reached silently.
- Is what I type uploaded anywhere?
- No. This page carries the whole tool as WebAssembly and runs it on your own device. A measurement is somebody's experiment and a load is somebody's building; none of it is sent anywhere.
Other tools for circuits
Ohm's law
Voltage, current, resistance and power: any two of them give the other two
Resistor colour code
The value from the bands, with the band count asked rather than guessed
LED resistor
The resistor a diode needs, the heat it makes, and the nearest part somebody sells
Capacitor code
Three digits into a capacitance and back, with the tolerance letter read too
RC filter
The corner frequency of a resistor and a capacitor, with the response either side of it
Power draw
What a set of parts draws, the supply it wants, and what a year of it costs
Battery life
How long a cell lasts at a draw, and how long it takes to fill again
All thirty-nine tools