The world of electronics procurement moves quickly, with supply chains sometimes shifting overnight, and last-minute substitutions often needing to be made.
For those working in this field, it is certainly crucial to know about capacitor values and how to convert them. Such awareness and skill could make the difference between a smooth project handover and expensive delays.
Who Is This Guide For?
You might be reading this article as a design engineer tweaking a Bill of Materials (BOM) for a new Internet of Things (IoT) device, or a procurement specialist who needs to source alternatives from suppliers.
These are both examples of professionals who need to be capable of performing rapid and accurate conversions between capacitance units.
The two-terminal electrical devices known as capacitors play a crucial role in a range of applications that require the storage and release of electrical energy, from voltage smoothing to signal filtering.
Moreover, there are many forms that capacitance notations can take, ranging from picofarads (pF) scribbled on a datasheet to microfarads (µF) in the catalogue of a supplier.
So, in this guide, we will seek to cut through the confusion by providing some practical tips on how to swiftly carry out capacitance conversions.
The Basics of Capacitor Value Notations
It is typical for capacitor values to be expressed in the International System of Units (SI), with the standard unit of capacitance being the farad.
This unit was named after the English physicist Michael Faraday (1791-1867), in recognition of his major contributions to the study of electricity and magnetism.
However, the farad is a very large unit for most electronic components. This explains why practical capacitor values tend to be expressed using prefixes, such as:
- Picofarads (pF), which are the smallest common unit, equal to 10-12 farads (F)
- Nanofarads (nF), which are equal to 10-9 F, or 1,000 pF
- Microfarads (µF), which are equal to 10-6 F, or 1,000 nF
When it comes to BOMs, notation mismatches – for example, between nF and µF – can lead to ordering errors. Fortunately, such mistakes can be avoided by those who know how to perform quick conversions between capacitance units.
Your ‘At A Glance’ Summary of Capacitance Conversion Multipliers
This table could be a handy reference for performing instant mental maths during procurement reviews:
| From \ To | pF | nF | µF |
| 1 pF | 1 | 0.001 | 0.000001 |
| 1 nF | 1,000 | 1 | 0.001 |
| 1 µF | 1,000,000 | 1,000 | 1 |
You can convert between these units by shifting the decimal point by the power of 10. For example, if you need to convert 47 nF to µF, you simply divide by 1,000, which gives you a result of 0.047 µF.
The Steps of Converting Capacitor Values for Your BOM
So, you’re building or revising a BOM using a tool like Altium or Excel. You will hopefully understand the importance of capacitance conversions for ensuring accuracy across datasheets from global suppliers.
Here, then, are the stages by which you can handle this efficiently:
- Identify The Source Notation
The first step will be to pull the value from your schematic or supplier spreadsheet. Be sure to take note of any tolerance (such as ±10%) or voltage rating, as these will need to remain constant during conversion.
- Carry Out the Manual Conversion
For example, if you need to convert 4,700 pF to nF, divide by 1,000. This would give you 4.7 nF. As for if a conversion of 220 nF to µF is required, again, divide by 1,000, to produce a result of 0.22 µF.
- Decode Marked Values
In the case of SMD capacitors, there will be a code that needs to be interpreted. A “226” marking, for instance, indicates 22 followed by six zeroes = 22,000,000 pF = 22 µF.
- Verify With Tolerance and Context
Remember to always cross-check against the actual needs of the circuit.
Speaking of verification, you can also convert capacitor values for BOM purposes using a capacitance converter like the one on the RS website. Doing so will enable you to double-check the accuracy of any manual calculations you have undertaken.
Capacitance Conversions Are Crucial for Ensuring Viable Substitutions, Too
If you need to swap capacitors during the procurement process – because of a stock shortage, for instance – be mindful of the importance of tolerance matching. Make sure you stick within ±5-20% of the original value to avoid circuit drift.
The voltage rating, too, will be a vital consideration; you should never go below the spec, but higher is fine. So, it would be acceptable to substitute 16V with 25V, for instance.
Hopefully, this guide will have helped affirm for you the importance of mastering rapid and accurate capacitor conversions. Doing so will greatly help you to keep projects on track, at a time when global supply chains aren’t always smooth and predictable.
