The following is an excerpt from our beginner-friendly book, When a Piano Falls in Your Lap: A New Owner's Guide to Used Pianos.

How to: Replace a broken string

A busted string happens fairly often with old pianos, and it absolutely does need to be corrected if you plan on ever playing your instrument. No strings, no sound.

But outside of major damage, this is the most difficult repair job you’d be likely to encounter. We recommend leaving this one to the pros, but it is possible to deal with it yourself. Tricky, but possible. If you think you’re up for the challenge, here are some of the basics you’ll need to know.

We’re not able to give you a step-by-step walkthrough of this process simply because it would take far too long. There are quite a few different approaches and methods to restringing, not to mention the practically infinite number of piano styles and model variables. This guide is more theoretical, with the intent of familiarizing you with the idea of restringing, than it is a walkthrough.

We highly recommend reading A Guide to Restringing by John W. Travis for a detailed guide through the full process. Piano Servicing, Tuning, and Rebuilding by Arthur Reblitz is another fantastic resource.

What you’ll see inside

The pins are located in the pinblock. This is where the ends of your piano strings are attached. If you’ll recall, the pins are used to tighten and loosen the strings while tuning, adding, or subtracting tension. Just below the pins, there’s a metal pressure bar. This is used to, well, add pressure to the strings and keep them in place. Further down, you will see two little pins called bridge pins. The string makes a Z shape across these pins. There might be a cloth ribbon woven through the strings, too. These are usually in the bass section. At the bottom of the string, there is the hitch pin.

You’ll notice that the treble section appears to have way more strings than the bass. You are not seeing double—there are three strings for each single note. Most all steel treble strings make a turn at the hitch pin and come back up. Both ends of the string are attached to its own pin. Some designs include a couple terminal strings (like bass strings). Have a technician replace those.

Bass strings, on the other hand, are single-strung. Instead of wrapping around the hitch pin, bass strings are terminal. They have one tuning pin in the block, and a loop at the other end goes over the hitch pin.

Upright pianos, grands, and spinets have different string configurations inside. The idea is the same—pin block, pressure bar, bridge pin, hitch pin—but the way they are aligned and work with their respective actions differs. We encourage you to get familiar with your piano and research your model’s configuration.

Replacing a piano string essentially means duplicating the strings you already have in place. If you’re missing just one string, use the intact strings as a template. It does matter which way the strings are wrapped, how they’re woven between the cloth, and the way they behave with bridge and hitch pins, so look carefully at your existing strings.

Nine times out of ten, the string will break at the tuning pin. You’ll see a little bit of coil up on the tuning pin and the rest of the string will be loose inside your piano. It’s very rare that the broken string would be missing entirely. The other time out of ten, the string could have broken at another point due to water damage, stressful playing, or other unexpected damage.

Selecting the correct piano string

Now, you can’t just dial up your local music shop and say “Hey, can I get a piano string?” Nor can you ask for a B. You can’t even narrow it down by asking for the third note from the right. You actually need to measure the string you need replaced. Remember, there are more strings than keys and the number of the string has nothing to do with the key or even the location inside the piano. And we know that pianos come in different shapes and sizes, so the length of the string can vary by quite a bit.

The new string you use will be as close to identical as the broken string as possible. In fact, if you still have the string, duplicate it as precisely as you can.

Steel strings, which are used in the treble section, come on a big spool and are sold in specific lengths. This is possible because the string is the same thickness and composition from end to end. When choosing your treble string, you will focus on finding the correct diameter and length; it’s not piano style or brand-dependent. This means that whether you have a brand-new Steinway or an antique stencil upright, you can use the same type of treble strings. Just make sure to choose a reputable brand and you’ll be good to go.

Using a micrometer will determine the exact diameter of the string, so make sure you have a good quality measuring device and know how to use it. Digital micrometers are preferable because they’re easier to read than an analog one. Either type can be found online or at hardware stores. Precise measurement is step one, but if you’re lucky, the gauge might be stamped or written on the plate near the tuning pins.

Bass strings are different animals entirely. Snakes, to be specific. They’re much thicker, harder to bend, come in specific lengths and sizes, and can be unwieldy to handle. They’re different from treble strings because they have copper windings. These windings are only around the part of the string that creates sound and is not wrapped around tuning pins, so measuring is a little different. You will need to determine the diameter, overall length, and copper winding length. Non-custom bass strings are sold over-wrapped, so the excess copper will need to be customized by whoever does the installation. Also, bass strings that terminal hitch pin loop on the end.

The bottom dozen or so bass strings have a double wrapping of copper. It’s extremely difficult to customize these double-wrapped strings yourself, so you’ll have to get in touch with your local tech or piano supply company for a special order. Many times, these companies will ask for the broken string so they can duplicate it exactly.

Steel treble strings are between 0.029” and 0.049” diameter, with only a .001” difference between strings. And yes, that thousandth of an inch makes a huge difference. In the unlikely event that your broken string is completely missing, you will need to measure the two strings on either side. Your missing string should be the measurement in between those two strings. Buy the size that closest matches your size.

Now, if you’ve measured your strings or done the math to determine the diameter you need, and your favorite fully stocked piano supply company doesn’t offer that size, buy the size that does exist. If you need, say, 0.0325”, you’ll have to decide if you want a 0.032” or 0.033”. Many tuners prefer to go with the thicker string because stretching the wire during tuning does thin it out ever so slightly.

Make sure your treble string is more than long enough. A good rule of thumb is to measure from the tuning pin to the hitch pin, double it, and then add about another foot. This will give you enough wire to wrap around both tuning pins.

Selecting a bass string can be a little trickier. Bass strings can be purchased by a set of measurements, and universal bass strings are available. They have extra overall length and extra copper winding that can be trimmed down and customized to your piano.

There are four measurements you’ll need when buying a bass string: distance from hitch pin to beginning of copper winding, length of winding, diameter of steel core, and the diameter of the wrapped part of the string. The most important measurement when purchasing is the diameter of the string measured around the winding. You can collect all this data and purchase a custom-made string, or you can prepare a universal bass string yourself. Custom is definitely easier, but DIYing it is possible if you’re very careful.

Once you’ve measured and acquired the correct universal bass string, you will need to score the copper winding and carefully peel it off the core. This process can take a lot longer than you imagine, because damaging the core means you will have to start over with a new string.

Side Note. Concerned your favorite piano supply vendor only stocks piano wire, but we’re telling you to buy piano strings? Nothing to worry about. String and wire are interchangeable terms in this case. Some vendors prefer one word over the other, but it’s the same product. 

Preparing for restringing

Should you attempt restringing, you will need your full tuning toolkit, a micrometer, a coil lifter and separator tool, needle-nose pliers, and a string stretcher tool.

Another thing to remember is, of course, safety. Always wear goggles and sturdy gloves when working with piano strings. Mechanics’ gloves are a great choice. This is to protect both you and the piano. The strings and tools can bite into your hands if you’re not careful, and your hands have oils on them that could affect the metal, encouraging premature rust. And remember, unloosened strings under high tension can snap like a rubber band. Except instead of elastic, it’s made of sharp, unforgiving steel. Always loosen the tuning pins before replacing a broken string.

Finally, only attempt to restring if you have a decent pinblock. If your old piano has a busted pinblock that has chemical staining around the tuning pins, or loose or missing pins, let a pro handle this job.

Sometimes a fresh string will sound slightly different from its neighbors. Brighter, some say. It’s a brand-new string in an old piano, after all, so it hasn’t been loosened and trained to behave like the other, more seasoned strings. With proper tuning and maintenance, your restrung piano will sound good as new—maybe even better.

To read more or learn other neat tricks for maintaining your piano, check out our new book, When a Piano Falls in Your Lap. Available now wherever you buy books.