How to Measure the Depth of a Well

Ever wondered how deep your well is? This is a question that many homeowners ask themselves at some point and it probably isn’t idle curiosity.

seeing the sky from the bottom of a well

Determining the depth of your well can be important for a variety of reasons, namely when it comes to determining what kind of hardware you’ll need for repairs, replacement costs, draw depth, and more.

But an average residential well can be dozens, even hundreds of feet deep.

This is not something you’ll be able to eyeball with any accuracy (assuming you can see the bottom!) and conventional measuring tools probably won’t work.

You’ll need to come up with alternative methods if you want to accurately measure the depth of your well on your own, but luckily it is pretty easy.

In this article, I will tell you about five methods that you can use to measure the depth of your well. Grab your notepad and let’s get to it.

Measuring Total Well Depth Using a Steel Tape

Tape Measure

The tape measure is definitely the most obvious tool you can use to measure the depth of your well, but there are a few things you need to take into account.

First, the tape measure needs to be long enough to reach from the top of the well all the way down to the bottom.

This might seem like a no-brainer, but it’s a legitimate obstacle as many residential wells are extremely deep, far deeper than the average tape measure is long!

Next, you’ll have to assess whether or not your good casing is wide enough to accommodate the tape measure.

Wires, pump piping, and other obstacles can make threading the rigid tape past them and all the way to the bottom an exercise in frustration.

Getting a false positive because your tape measure gets jammed on something is also entirely possible.

Lastly, this can be a fatiguing method because you’re probably going to be holding the tape measure directly over the opening of the well while you measure.

Most tape measures are not quite flexible enough to be held at an off-angle while you feed them down into the well.

Also, make double sure you don’t use a tape measure with a magnet on the hook, or else you’re going to be facing a ton of frustration as it jumps and binds on everything.

If you are dealing with a well that you know is relatively shallow, the tape measure can still work just fine and will have the added benefit of providing you with an accurate measurement.

For deeper wells or ones with a particularly narrow casing, I would try a different method.

How to easily measure bore well depth and static water level

Weighted Line

Another option and one of the simplest is to use a weighted line.

This is nothing more than a line of twine, cord, or string that has a hefty weight attached to one end, lowered down the well until it hits the bottom.

At that point, you take the slack out of the line, mark it where it reaches the top of the good casing, and then retrieve the line to make your measurement easy.

It sounds simplistic, primitive even, but despite that, this is one of the most effective and reliable methods for measuring a deep well.

Compared to other methods on this list it is minimally labor-intensive, highly affordable, and produces a reasonably accurate measurement.

That being said, there are definitely a few key factors that you should know about before attempting it.

The main advantage of this method is that you can easily measure the depth of the well by simply measuring the length of the line that’s left above ground (if you have a line of known length) or by marking and measuring the line when it bottoms out in the well (with a line of indeterminate length).

The main downside is that it can be difficult to keep the weighted line from getting tangled on obstacles inside the well casing though not as difficult as with a tape measure.

There are a few other things to consider before you utilize this method. Remember that your well is responsible for supplying your home with water, and probably drinking water at that.

Accordingly, any materials that you lower into the well should be non-toxic, especially when you consider that an accident or mishap might result in those materials falling down into the water and staying there forever!

Extra-large fishing sinkers are popular for use with this method, but you must never use any sinker or other weight with lead in it or else dangerous metal contamination will start building up in your household water over time.

I recommend a steel or ceramic sinker for the purpose, that way should it become lost or stuck you won’t have to worry about serious contamination in your water.

ASK US ANYTHING: Finding water depth! Soundings, lead lines, fathoms and more!

Acoustic Sounding

An acoustic well-sounding tool is another option for measuring the depth of your well.

This is a tool that utilizes high-intensity sound waves to determine how far away the device is from the surface of the water by running a simple calculation of time over a distance utilizing the reflected waves.

In operation, they function on the principle of echolocation akin to what a bat uses to navigate at night.

The advantage of this tool is that it is relatively easy to use and can be quite accurate.

It has the added benefit of not extending anything physical down into the good casing itself which might become tangled, stuck, or otherwise get lost.

This is great for minimizing the risk of contamination to the water inside the well.

The downside is that the tool can be expensive, with better and more accurate tools being more and more expensive to buy or rent.

Also, these tools can only read to the surface of the water in the well. If you have a deep well that has a high water level, you won’t be getting all the information you need to determine just how deep the good casing itself is.

Due to these inherent limitations, several readings might be required at different times of day, in case of differing water levels or during periods of high usage to produce enough data to make an accurate determination.

Nonetheless, these tools are something of an industry-standard, minimally invasive, if at all, and generally reliable so long as the operator is skilled.

With a little bit of practice and homework, you might use one of these acoustic sounding tools to determine the depth of your own well at the click of a switch.

Laser Distance Measurement: Time-of-Flight with PRT

Laser Ranging

Finally, there is the option of using laser ranging. A laser rangefinder can emit a beam of coherent light and then determine the distance from the ranging unit to the target with impressive accuracy.

This is an ideal option for measuring distance or depth, as it does not require any physical contact with the target surface.

Despite how increasingly common these devices are, they do have some serious drawbacks which make them less than suitable for certain applications.

The downsides of laser rangefinders include expense and the fact you need to have a clear and uncluttered line of sight from the top of the well to the bottom in order to obtain an accurate reading.

A narrow well casing or one that has a bunch of obstacles inside it might mean that you practically cannot achieve the line of sight to the surface of the water necessary.

Only wells that are fairly shallow will allow one of these to be used handheld easily. Expect to need a tripod arrangement or other mount to hold it steady enough.

Also, like the acoustic-sounding tool, a laser rangefinder can only produce a measurement of the surface of the water, and this might prove inadequate for wells with a high water level that is otherwise quite deep.

But the good news is a laser rangefinder works quickly and easily, so long as you have the clear line of sight mentioned previously.

Easy to aim and easy to operate, a click of a button will produce an unambiguous and highly accurate measurement once these prerequisites are met.

Also like the aforementioned acoustic sounding tool, a laser rangefinder does not insert any physical probe or other objects into the good casing which might become stuck or contaminate the water within.

For larger diameter wells or wells with a tidy interior installation, a laser range finder might work perfectly and quickly for measuring its depth.

Call the Drilling Company

Hey, it is technically still a DIY method! In seriousness, before you go through all the aggravation and potential guesswork of measuring the depth of your residential well yourself, try to track down the contact information of the drilling company that installed the well.

Although not a guarantee, many such professional companies keep extensive records for future reference, and one phone call and perhaps a small convenience fee could give you precise measurements of every dimension of your well, and possibly your water table also.

Whatever your purpose is for measuring your well in the first place, having plentiful, accurate data on hand with a phone call or email will save you a ton of time and money over even the simplest of methods.

Before you break out your own tools, try to find out who drilled the well and give them a ring.

How Deep Does it Go?

Now that you know about five different ways to measure the depth of your well, it’s time to choose one and see what you find.

From the simple to the high tech, there is a method for every budget and every installation. With a little bit of effort, you’ll be able to accurately determine the depth of your well in no time.

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1 thought on “How to Measure the Depth of a Well”

  1. I made a DIY acoustic measurement of well depth. I took my cell phone and used the Hokusai 2 app to get an audio recording of things. I took a piece of bubble wrap and popped it over the well while recording the sound. Then I used the app to chop out the “ringing” part just after the pop. It’s easy to spot as a bunch of oscillations just after the pop and lasts a fraction of a second. Then I saved that as an m4a sound file. Then I took an FFT (Fast Fourier Transform) of the m4a file. There are free apps online that will do this. You should get some clear peaks in the FFT, all separated by the same number of points, and you can measure how many points between the peaks and take an average. Then you can use the formula:

    L = n v/(2 d fs)

    where
    L is the depth from the top of the well to the top of the water
    n is the number of samples in your recording (I had 31,000)
    v is the speed of sound in the well (I use 1100 feet per second which is the speed of sound at 50 degrees F)
    d is the number of points between the peaks in the FFT (I averaged 4 peaks to get 29)
    fs is the sampling rate of the audio (44,1000 samples per second)

    using just n and d, you can use

    L = 0.012755 n/d

    Using my numbers n=31000 and d=29, I measured the depth of the well to be 13.3 feet and using a weight and a string I got 13.4 feet.

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