I recently brought home a shiny new 20v Dewalt drill and I couldn’t have been more excited to test it out. Needless to say, it was time to finally complete that home improvement project — only, the drill’s battery didn’t last long enough on a single charge.
This left me wondering about how many amps a cordless drill uses. Because if I could figure out how many amps my drill uses, I could figure out how long it’ll last on a charge.
The simple calculation for how many amps a cordless drill uses is Watts divided by Volts.
But in this post, I’m going to break down what each of these measurements means (in simple terms) and how to figure out how many amps your drill uses.
By the time you’re done reading this post, you’ll know exactly how long your drill will last on a charge. Here’s a hint: It all has to do with the Amp Hour rating of your battery, and that means nothing unless you know the drill’s amperage draw.
Okay, let’s get to it!
What are Amps?
There are a few terms that might be confusing when you’re trying to figure out which cordless drill to buy or how long your drill will last on a charge.
Amperes (or amps) are a unit of measure, and they measure electrical current.
I can almost hear your next question. “Okay, so then what are volts?”
And this is a natural next question because the voltage is clearly an important measurement used in cordless drills. You’re probably looking to buy either an 18v or 20v cordless drill, so which is better?
So, what’s the difference between amperes and volts?
Here’s the simple answer: Although both measure electrical current, amperes measure the speed of the current while volts measure the force.
Imagine water running through a pipe. Voltage would be similar to measuring the water pressure while amperage is more like measuring the flow rate of the water (the speed in which it’s flowing).
And now for the last measurement, you’ll need to know in order to figure out your drill’s amperage draw: Watts. Watts is simply a measure of electrical power.
Now, for that weird measurement on your drill’s battery.
What Are Ampere Hours?
Ampere hours (Ah) are a measure of the battery’s energy storage. A fully-charged battery will usually run for as long as the ampere-hour rating of the battery.
For example, a 3Ah battery will run 3 amps for one hour. If your cordless drill runs two amps, that same battery will last half as long on a charge.
You should find the Ah rating on the battery itself. And if you’re shopping for new drills, it should be listed in the product description or on the box.
How Many Amps Does A Cordless Drill Draw?
Now, to figure out how many amps your cordless drill uses, let’s go back to the pipe analogy.
The more pressure (volts) the water is under, the faster it will go (amps).
So, a 20v cordless drill will always draw more amps than an 18v cordless drill. You’ll also need a battery that’s rated for the voltage of your drill.
And since the amperage will vary based on the wattage of the drill’s motor and the voltage of the drill’s battery, you’ll need to perform a simple calculation to determine the amperage draw for your drill.
How to Calculate Amperage Draw
Check to see the wattage that the drill’s motor is rated for.
Divide the watts of your cordless drill’s motor by the total number of volts on the battery. This will give you the amperage draw of the drill.
For example, an 18v cordless drill with a 250-watt motor will draw about 14 amps.
Now, let’s say your battery is rated 3Ah.
Remember that a 3Ah battery will draw1 amp for 3 hours. So, if you’re running 6 amps, you can expect to have to recharge after about 30 minutes. See the table below to check how the current draw affects run time.
So, now that you know how to figure out how many amps your cordless drill uses, you can find this information for virtually any drill. It may help you figure out what type of battery to buy or even whether you want an 18v cordless drill or a 20v drill.
It’s all about what’s important to you. If it’s important for your drill to last longer on a charge, you’ll want to choose a lower voltage and a higher Amp Hour rating.
If it’s more important for your drill to be powerful, choose a higher voltage and higher Amp Hour rating.
If you are interested in this topic you can check out the following article I wrote: Are Cordless Drill Batteries Interchangeable