Use this interactive tool to calculate the power cost for your Raspberry Pi.

A customer asked me an innocent question:

I would like to use a Raspberry Pi for the two following purposes:

a) Pi Hole to filter ads 
b) Baikal-Server for Carddav and Caldav

Which Pi would you recommend, considering power usage, heat development, etc.?

My answer required some research:

For me it was clear that the Pi 4 / 4 GB  would be the server of my choice, of course with the FLIRC case for passive heat dissipation. No noise, no moving parts. GBit Ethernet, … but could I recommend the Pi 4 to the customer in good conscience? Can people actually afford to operate the Pi 4 non-stop, 365 days a year, 24 / 7?

The answer will surprise you. I was surprised myself!

Basics

We’ll start out for some basics for all those of us who have put high school physics behind them a long time ago:

• Ampere: this is the power current (how much electrical power flows through a conductor or device – imagine this as number of electrons flowing through the pipe per second)
• Volt: this is the voltage (you can imagine this as the pressure under which the electrons flow – similar to water pressure in a pipe. Same amount of water under different pressure can be pleasant in your bath tub… or cut through steel)
• put together, Volt and Ampere yield Watt, the actual power (defined as work per second): 1 W = 1 V * 1 A

An important thing to keep in mind is that Watts are independent of the voltage, and independent of direct or alternating current being used (DC or AC) – it is the actually delivered power. 

Usually utilities charge in kWh – kilowatt hours. This is the power which is delivered is summed up across the time it was delivered. The kilowatt hours are the actual work the power utility delivered to your house. 

Pi 4 power usage

The Pi 4 isn’t a light bulb. It does not use (and deliver) the same amount of power consistently over time. Depending on what you are using it for, parts of its SoC (the silver chip on the Pi, the ingenious device at the core of the magic of the Pi) will be turned on and off.  

The Pi 4 can also be compared to a human being: if the person is resting, for instance watching a movie on their KODI media centre, they need much less energy than if they would run a marathon. Still, it’s the same person.

For this reason it is important to look at idle power consumption of the Pi 4, but also at the power consumption under heavy load. 

An important thing to also keep in mind before we start: this does not include external devices (USB devices which draw power, for instance external harddrives, SSDs, etc.) – but you can easily add them using the formulas I provide below.

I am using the power measurements of the excellent Alex Eames of Raspi.TV as base for my calculations. Thank you very much, Alex!

The Pi 4 draws the following currents:

• 575 mA while idling
• 885 mA while LXDE is being loaded
• 600 mA to view 1080p video 
• 640 mA to record 1080p video

We take the bottom and top values, 575 mA and 885 mA. Power usage of the Pi 4 averaged over time should be something in between. 

Because the official USB C power supply supplies 5,1 V, we can turn the mA (m is for milli, a thousandth) into Watts: 

• 2,93 W while idling
• 4,51 W while the Pi 4 is loading LXDE

The Pi 4 draws between 3 and 5 W on the average.

The power supply

We should not omit an important factor which plays into calculating the actual power drawn from the utility! The power supply itself. 

Even though the official USB C power supply is very efficient, it is not perfect. It uses up some power for it’s own circuitry.

The USB C power supply was certified according to the Effieciency Marking Protocol (a standard introduced in the USA). Here’s a PDF with more background information. 

This standard was launched after people were shocked to see that a lot of inefficient power supplies (using linear regulators) were using up to 50 % of the power themselves – independent of whether the device it was supposed to power was active or not! It was predicted that around 2010, the power supplies alone would use up to 30 % of the total power in the USA. Of course, something had to be done about this situation – which lead to this standard. 

The official power supply has a 5,1 V voltage, and a maximum of 3 A of current which it is able to provide. This is a maximum power of 15,5 W (5,1 V * 3 A) which it is able to supply to the Pi. Please keep in mind, we are working with averages above – the Pi will draw in a lot of power in very short bursts, which requires more than the 4,51 W to be available. Averaged over time, even under load, we should see the power draw Alex measured. Furthermore the power supply also has to power USB devices if you have any attached to the Pi, which is budgeted in. 

According to the standard (VI) the official Pi 4 power supply may draw a maximum of 0,1 W when idling itself – that is no Pi is attached.  (The actual value in the datasheet is 0,075 W maximum)

The standard further demands, that if the Pi 4 is beign powered, that the power conversion efficiency must be at least:

0.0834 x ln ( Pout) – 0.0014 x Pout + 0.609

This is the natural logarithm, Pout is the power output to the Pi. Luckily, there’s Excel which can crunch the numbers for us:

• a minimum of 69 % efficiency for the Pi 4 when idling 
• a minimum of 73 % efficiency for the Pi 4 while it is loading LXDE

If the Pi 4 is working hard, the power supply is required to be more efficient – an interesting insight! 

According to the datasheet of the Pi 4 power supply, the minimum efficiency at 10 % load is 72 %, and minimum of 81 % at 100 % / 75 % / 50 % / 25 % load. I will continue to use the values I calculated above, as they should be applicable to any other power supply with the VI certification. 

At the power socket, the Pi 4 actually draws:

• 4,22 W power when idling
• 6,20 W power while LXDE is loading

Calculated for a whole year

A day has 24 hours, the year has 365 days (most of the time). The kilowatt hours are what they say they are: 1000 W * amount of hours:

• 36,98 kWh power usage when idling per year
• 54,28 kWh power usage when loading LXDE per year
• 0,88 kWh if the power supply for the Pi 4 would be plugged into the power socket 365/24/7 – without Pi. (Actual value even lower due to datasheet giving 0,075W maximum)

Please simply tell me how much it costs

The energy prices currently fluctuate. In Germany, they are amongst the highest in Europe – even considering income adjustment. I have used a price of 32,8 Cent pro kWh for the calculations, according to these two sources. The price might be lower for you – please redo the calculations in this case! 

I will also include pricing I’ve estimated for the UK – which is significantly lower. I’ve used this site as a source:

• 13 pence per kWh on average
• 20 % VAT
• 1,17783 € / GBP
• = 18,39 Euro-Cent per kWh

Are you ready for your mind to be blown?

• 12,13 € power cost for the Pi 4 when idling 365 / 24 / 7
  • 6,80 € power cost in Great Britain
• 17,80 € power cost for the Pi 4 under load, 365 / 24 / 7 (all the year long!) 
  • 9,98 € power cost in Great Britain
• 00,29 € power cost for the USB C power supply, if it is simply plugged into the socket, no Pi, for a whole year
  • 0,16 € in Great Britain
  • note this value is actually even lower, due to the Raspberry Pi power supply being even more efficient!

And all this including the VAT! 

The surprising message of this article (which I never expected myself, although I’m writing it!):

A Pi 4 is a clever investment to save money on power!

This blogpost by codinghorror can give us a rough approximation of what a desktop computer uses in power, in comparison. The article is from 2007, and talks about 120 to 150 W of actual usage (pre power-supply efficiency). But let’s say, out of fairness, that you use a really power-efficient x86 computer as mini-server. Possibly an old notebook. And that this x86 computer (power draw from the socket) uses only 10 times the amount of a Pi 4:

• 62 W on average
• 543 kWh per year
• 178,14 € power cost per year for your really power efficient x86 server
  • 99,87 € power cost in Great Britain

The actual difference between the Pi 4 and the “efficient x86 server” out of your pocket, just for power usage, are 160,34 € per year! Depending upon how “fat” your server is, how inefficient it’s power supply is, you could be looking at even higher savings! 

To be fair, I should admit that there are also quite power efficient Intel Atom SoCs, which draw less power – according to this article, we’re somewhere between 10 to 15 W idling. Still about two to three times more than the Pi!)

Our Pi 4 comfort set saves you money in the first year of operation already!

When operating a small server 24/7, our Pi 4 comfort set would save you money, compared to a classic desktop PC as server:

• Pi 4 Comfort Set: 95 €
• shipping (within Germany): 4,99 €
• power usage: 17,80 €
• Total cost in the first year: 117,79 €
• You save, xompared to x86: 60,35 €

YES! You save money, in the first year of ownership already! Even considering the purchasing cost of the Pi 4 – simply by saving on power!

Why not use the savings to buy a second Pi 4 / 4 GB as a present for a friend? You will actually be giving a gift of money – with a yearly profit in power cost savings, year after year!

The Pi 4 is supporting our green planet – time to get rid of our old x86 servers which are running in idle most of the time anyways (not really delivering their full capacities / possibilities) – just the power savings alone might justify a purchase of a Pi 4!

Note: People who are lucky to have cheaper costs of power, as in Britain, wil be able to realize the savings within two years, and benefit year over year after that! Few investments pay that quickly for themselves, and start yielding benefits. 

Tags: Conserve power, Ecoonomy, Green energy, Green planet, Ökologisch, Ökonomisch, Pi 4, Power efficiency, Power efficient computing, Save power, Server, Strom