Science and Electronics Calculators
These calculators cover the formulas used at the workbench and in the lab. Ohm's Law solves voltage, current, resistance and power from any two values, the Resistor Color Code Calculator reads 4, 5 and 6 band resistors in both directions, and the Voltage Drop Calculator checks whether a wire run is long enough to cause trouble. For chemistry, the Molarity and Molecular Weight Calculators handle concentrations, dilutions and molar masses, and the Half-Life Calculator works through exponential decay.
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All Science & Electronics (8)
Ohm's Law Calculator
Voltage, current, resistance and power from any two valuesResistor Color Code Calculator
Resistor value and tolerance from 4, 5 or 6 color bands, and backVoltage Drop Calculator
Voltage drop in copper or aluminium wire by gauge, length and loadMolarity Calculator
Molarity, mass, volume and dilutions for solutionsMolecular Weight Calculator
Molar mass of a chemical formula with element breakdownHalf-Life Calculator
Remaining quantity, half-life or elapsed time for exponential decaySpeed, Distance and Time Calculator
Solve for speed, distance or time in any unitsDownload Time Calculator
How long a file takes to transfer at a given bandwidth
Which tool do I need?
Find the resistor value from its colour bands
Pick the bands to read the resistance and tolerance, or enter a value to see which bands to look for.
Work out the current a circuit draws
Enter any two of voltage, current, resistance and power to solve the other two.
Make a solution of a set concentration
Find the molar mass of the compound, then the mass to dissolve for the molarity and volume you need.
Estimate how long a large upload will take
Enter the file size and connection speed to get the transfer time, with an allowance for protocol overhead.
About Science & Electronics
Two everyday physics tools complete the set. Speed, Distance and Time solves any one from the other two in mixed units, and the Download Time Calculator shows how long a file takes over a connection, including the difference between megabits and megabytes that makes advertised speeds look faster than they are.
Inputs accept SI prefixes and common units, and every result shows the formula used. Electrical results assume steady-state DC or simple resistive AC loads; real circuits, motors and long cable runs may need a fuller analysis by a qualified electrician.
Guides
- Ohm's Law, Resistor Color Codes and Voltage Drop ExplainedHow voltage, current, resistance and power relate, how to read 4, 5 and 6-band resistors and pick E-series values, and how to size cable for 3% voltage drop.
- Molar Mass, Molarity, Dilutions and Half-Life: Lab MathsFrom a chemical formula to grams on the balance: molar mass with IUPAC atomic weights, molarity and C1V1 = C2V2 dilutions, and exponential decay with half-lives.
- Speed, Distance and Download Time: Getting Rates RightTravel time and transfer time are the same sum. Why averaged speeds mislead, why 100 Mbit/s is 12.5 MB/s, GB versus GiB, and what overhead really costs.
Frequently asked questions
Why does my download take longer than the advertised speed suggests?
Speeds are sold in megabits per second while files are measured in megabytes, and there are 8 bits in a byte. Protocol overhead and other traffic slow things further.
How do I read a five-band resistor?
The first three bands are digits, the fourth is the multiplier and the fifth is the tolerance. Read from the end with bands grouped closer together.
What voltage drop is acceptable in a circuit?
A common guideline is no more than 3% on a branch circuit and 5% in total, but the rules depend on your electrical code and the equipment.
Where do the atomic weights in the molar mass calculator come from?
From the IUPAC standard atomic weights, using conventional single values for elements whose weights vary slightly in nature.