Why Is My Raspberry Pi 4 So Slow? 6 Causes and Fixes

Quick answer: Why is my Raspberry Pi 4 so slow? Most of the time it’s one of three things: a power supply that can’t hold 5 V, a chip that’s throttling because it’s too hot, or a slow SD card. Run vcgencmd get_throttled first. A result of 0x0 means power and heat are fine, so the bottleneck is likely storage or software.

A Pi 4 that crawls isn’t usually broken. It’s protecting itself. The firmware deliberately slows the processor when the voltage dips or the temperature climbs, and it doesn’t always tell you loudly.

So I’d start by asking the Pi what it saw. One command does that.

Check This First: vcgencmd get_throttled

Open a terminal and run:

vcgencmd get_throttled

The Raspberry Pi documentation lists what each bit means:

Bit	Hex value	Meaning
0	0x1	Undervoltage detected
1	0x2	Arm frequency capped
2	0x4	Currently throttled
3	0x8	Soft temperature limit active
16	0x10000	Undervoltage has occurred
17	0x20000	Arm frequency capping has occurred
18	0x40000	Throttling has occurred
19	0x80000	Soft temperature limit has occurred

Bits 0 to 3 describe right now. That’s live status. Bits 16 to 19 mean it happened at some point since boot. A reading of 0x50000, for example, means undervoltage and throttling both happened earlier, even if things look fine this second.

Two more commands help, and I’d run both: vcgencmd measure_temp shows the chip temperature, and vcgencmd measure_clock arm shows the current CPU frequency.

Why Is My Raspberry Pi 4 So Slow? The 6 Causes

Here they are, most likely first. My take: power and heat are the two causes the firmware itself reports on, which is exactly why the throttle check comes before anything else.

1. The Power Supply Is Too Weak

This is the big one. Honestly, I’d bet on it. The Raspberry Pi documentation recommends 5 V at 3 A for the Pi 4, using the official 15 W USB-C supply, and notes that all models need a 5.1 V supply. Not every phone charger is built for that.

The board watches for the voltage dropping below 4.63 V (plus or minus 5%). When it does, the kernel logs it. The official Raspberry Pi magazine adds that a small lightning bolt icon appears on the desktop.

Cables matter too. More than you’d think. The docs say recommended voltages are measured at the plug, so a long or thin cable eats into your margin.

2. It’s Overheating and Throttling

The docs spell out the limits. Between 80°C and 85°C, the Arm cores are throttled back progressively. At 85°C, both the Arm cores and the GPU slow down.

A bare board in a closed plastic case on a warm shelf can get there under a long compile or a video call. Most people won’t notice the number. They just feel the lag.

3. The SD Card Is Slow or Worn

Raspberry Pi says faster storage with higher read and write speeds improves overall performance. A cheap or old card turns every app launch into a wait. Boot takes ages too. It’s the bottleneck I think people blame least.

4. Too Many USB Devices on Board Power

According to the docs, the Pi 4’s USB ports supply 1.2 A total, shared across all of them. Hard drives and several accessories can push past that, and they pull the supply voltage down with them.

5. Old Software

An outdated system misses firmware and driver fixes. Rarely the whole story. Still cheap to rule out.

6. The Wrong OS for the Job

The full desktop runs a lot in the background. When you use the Pi as a server, a sensor logger or a home automation hub with no screen attached, all that graphical overhead buys you nothing at all.

How to Fix It

Work down this list. The trick is to change one thing at a time: if get_throttled showed a power or heat bit, start with that fix and skip the rest until you’ve retested.

Fix the Power

1. Use the official Raspberry Pi 15 W USB-C supply, or one rated at 5.1 V and 3 A.
2. Use a short, decent cable. Don’t power the board through a cheap USB hub.
3. Reboot, put the Pi under load, then run vcgencmd get_throttled again. You want 0x0.

Fix the Heat

1. Check the temperature under load with vcgencmd measure_temp.
2. Add a heatsink, a fan, or a case built to manage CPU temperature.
3. Give it air. The Raspberry Pi magazine notes that standing the board vertically improves airflow.

Don’t overclock a Pi that’s already throttling. In practice you’ll just hit the heat limit sooner.

Fix the Storage

1. Move to a faster card. Raspberry Pi suggests its own official microSD card if you’re unsure, and recommends at least 32 GB for the desktop OS.
2. Or boot from a USB SSD. The docs say the Pi 4 supports USB boot as long as USB is in the boot order. The default order tries the SD card first, then USB.
3. To change the boot order, open raspi-config, go to Advanced Options, then Boot Order. Early Pi 4 boards may need a bootloader update before USB boot works.

Preparing the SSD on a Windows PC and it won’t show up? See external SSD not recognized in Windows 11.

Power Hungry USB Gear

Move hard drives to a powered USB hub or a drive enclosure with its own power. The docs say attaching more than one disk typically needs extra external power anyway.

Update the System

Run these two commands, one after the other:

sudo apt update

sudo apt full-upgrade

Raspberry Pi recommends full-upgrade over plain upgrade. Check free space first with df -h.

Match the OS to the Job

For headless projects, install Raspberry Pi OS Lite, the command-line version. The docs say it needs as little as an 8 GB card, and you skip the desktop load entirely.

Raspberry Pi 4 Still Slow After All That?

If get_throttled reads 0x0, the temperature stays well under 80°C, and you’re on a good card or SSD, the Pi may simply be at its limit for that task. Heavy browser tabs and high-resolution video can be a lot to ask of a small board.

The other option is a clean start. Reflash the OS with Raspberry Pi Imager and add your apps back one at a time. Our guide to how to reset Raspberry Pi 5 walks through Imager, and those steps work the same way for a Pi 4.

Stop and unplug if you smell burning, see a swollen or melted connector, or the supply gets too hot to touch. Those aren’t speed issues. Replace the supply before you power the board again.

More Pi and Arduino guides live in our DIY electronics section.

Frequently Asked Questions

What Does 0x50000 Mean in vcgencmd get_throttled?

It means bit 16 (undervoltage has occurred) and bit 18 (throttling has occurred) are set. Both happened since boot, even if neither is active now. Fix the power supply first, then retest under load.

At What Temperature Does a Raspberry Pi 4 Throttle?

The docs say Arm cores throttle progressively between 80°C and 85°C. At 85°C, the Arm cores and the GPU are both throttled.

What Power Supply Does a Raspberry Pi 4 Need?

Raspberry Pi recommends 5 V at 3 A, using its 15 W USB-C supply. All models need a 5.1 V supply, measured at the plug.

Does a Raspberry Pi 4 Need a Fan?

Not always. If measure_temp stays below 80°C under your normal load, you’re not throttling. If it climbs higher, add a heatsink, a fan or a cooling case.

Is an SSD Faster than an SD Card on a Raspberry Pi 4?

Raspberry Pi says faster storage improves overall performance, and the Pi 4 can boot from USB. A USB SSD is a common upgrade over an SD card.

Last updated: November 10, 2026. Sources: Raspberry Pi documentation: hardware, power and thermals, Raspberry Pi documentation: vcgencmd and updates, Raspberry Pi documentation: getting started and Raspberry Pi magazine: overclocking Raspberry Pi 4.