As a former executive in multinational companies in the automotive industry for many years, I highly recommend for your safety to check these 6 signs when to replace brake pads.
Most online articles on when to replace brake pads lack simple explanations and clear actions to take. I set out to fix that.
Here are the 6 signs:
Do not hesitate to consult a local qualified professional.
Keep reading to find out when to replace brake pads.
#1: Dashboard Indicator Light
It’s very easy to get informed of worn brake pads. Indeed, cars with brake-pad sensors inform the driver via a light in the dashboard or via a message usually displayed on the startup phase.
Your car may already have an indicator light on the dashboard that will light up as a sign to replace the brake pads. So, look at your owner’s manual to check if your car is equipped with a low-pad warning system.
Your car may only show a general brake warning light when your parking brake is not engaged. In this case, you have to consult a brake expert to diagnose the right issue on your brake system. 
#2: Longer Stopping Distances
Your braking system must always respond adequately to your stops. While applying your brakes, you expect that your car stops at the right distances. If not, if you’re experiencing longer stopping distances, maybe your brake pads are worn down and need to be replaced by new ones.
Your brake fluid can also cause longer stopping distances. Regardless of the cause, you have to fix that issue and do not hesitate to ask for professional help.
This sign could be life-threatening. If you can’t slow down your car when you have to, you put yourself and others at severe risk. Your vehicle won’t stop at the right distance and at the right time; that’s an accident waiting to happen. 
#3: Brake Pad Thickness
You can visually inspect your brake pads and measure their thickness. 12 mm is the standard thickness size for most new brake pads. Usually, the first 6 mm is carefree.
In most cases, it’s highly recommended to replace brake pads from 3 mm to 4 mm. You still need to know and stick to your manufacturer’s recommended minimum brake pad thickness.
Mainly, two factors impact the lifespan of any brake pads: the vehicle type, and the driving style. So, 50k miles should be considered as an average for usual cases, while 20k miles may be more reasonable for other circumstances.
With a lower thickness, the brake pads lose their performance dealing with heat. The lower the thickness, the greater the risk of cracking.
#4: Squeaking Noise
Squeaking noise is a warning sign alerting you to replace your brake pads ASAP. Any further delay would cost you more repairs money and would increase the probabilities of accidents.
Brake pads embed a metal burr. Its purpose is to contact the rotor at 3 mm. This metal-on-metal contact is the cause of the squeaking noise you might hear when the brakes are engaged.
Most of the time, squeaking noise is the first signal you will notice when it’s time to replace brake pads. 
#5: Grinding Noise
We hope you’ll never hear this kind of noise while engaging your brake pedal!
Grinding noise like metal grinding probably implies your brake pads are worn completely and are rubbing into your rotors. It’s time to replace your brake pads ASAP.
As your brake discs and calipers are on direct metal-on-metal contact, driving in such a situation would cause more damage to your braking system, higher repair costs, and unsafe road trip for you and for all the road users around you.
Another sign when to replace brake pads!
If you feel vibration when you apply brakes, more likely your rotors are warped and have caused a glaze on your pads.
Once your brake pads are glazed, and even if their thickness is still in the carefree range, you have to replace them ASAP. You need professional help as you may need to check also your rotors.
The Bottom Line
Brake pads are critical parts of your car braking system. For your safety and your money-saving, you have to inspect them regularly and act as soon as possible. The 6 signs above are a great help. I recommend consulting a local qualified professional when to replace brake pads.
Do you want to learn more about bleeding brakes? Check out our guide on how to bleed brakes to learn the complete process and choose which of the 5 explained methods will fit your needs.