20 centimeters in inches for car speakers: how to choose the right size

Question "20 speakers - how many inches is that?" often arises among car owners who want to upgrade their audio system, but are faced with confusion in units of measurement. The fact is that speaker manufacturers traditionally indicate the diameter in inches (inch), whereas in Russia and the CIS countries it is more common to operate centimeters. An error in converting dimensions can lead to the fact that the purchased speakers simply will not fit into the standard seats or will require modifications to the panel.

This topic is especially relevant for owners of domestic cars (for example, VAZ 2110/2114, GAZelle) and old foreign cars, where the dimensions of the dynamic heads were often indicated in centimeters. In this article we will look not only exact conversion of 20 cm to inches, but also the nuances of selection by diameter, compatibility with popular car models, as well as typical mistakes that spoil the sound instead of improving it.

Let us immediately note: 20 centimeters ≠ 8 inches (a common misconception!). The correct translation and why it is important - read on.

How to convert 20 cm to inches: formula and nuances

To accurately convert centimeters to inches, use a simple formula: 1 inch = 2.54 cm. Accordingly, to find out how many inches are 20 cm, you need to divide 20 by 2.54.

20 cm ÷ 2.54 ≈ 7.87 inches. This is the meaning round to 7.9" or 8" for marketing purposes, but in practice a difference of 0.13 inches can be critical during installation. For example, speaker 8" (20.32 cm) may not fit into the opening designed for exactly 20 cm.

Why is accuracy important?

• 🔧 Seat: Stock openings in doors or panels often have tight tolerances. The speaker is 0.3 cm wider - and the metal will have to be bored.
• 🎵 Acoustic screen: The gap between the speaker and the car body affects the quality of the bass. Too large or small a diameter will distort the sound.
• 💰 Cost of improvements: Remaking a seat to a non-standard size will cost 1.5–3 thousand rubles (depending on the car model).

In car audio it is customary to indicate nominal diameter, which may not coincide with the physical one. For example, speaker Pioneer TS-A1670F labeled as 6.5", but its actual diameter is 16.5 cm (6.5 × 2.54), and the mounting diameter is 14.8 cm. Always check with the seller bore and outer diameter (they may differ by 1–2 cm!).

Conversion table: centimeters vs. inches for car speakers

To avoid mistakes, use a table with the most common sizes. Please note: first value - nominal size in inches (as indicated on the packaging), second - actual diameter in cm.

Nominal Size (inches)	Actual Diameter(cm)	Bore diameter (cm)	Example of car models
6.5"	16.5	14.5–15.0	VAZ 2108–2115, Renault Logan, Kia Rio
7"	17.8	15.5–16.0	GAZelle, UAZ Patriot
7.9" (20 cm)	20.0	18.0–18.5	VAZ 2121 (Niva), Mosvich 2141
8"	20.3	18.5–19.0	Ford Focus II, Opel Astra H

⚠️ Attention: If your car has speakers 20 cm, this does NOT mean that you can bet 8" (20.3 cm). Example: in VAZ 2121 standard hole for front speakers - 19.8 cm, therefore 8" won't fit without modifications. Always measure bore diameter (inner circle of hole) and depth (so that the speaker does not rest against the door mechanisms).

To measure use caliper or flexible ruler. If there is none, wrap a thread around the hole, mark the circumference, then divide it by 3.14 (Pi) to get the diameter.

Compatibility of 20 cm (7.9") speakers with popular cars

Speaker diameter 20 cm (7.9") - a rare size that is found mainly in domestic cars and some European models of the 90s - early 2000s. Here is a list of cars where they are installed regularly (without modifications):

• 🚗 VAZ 2121 "Niva" (front doors, rear parcel shelf)
• 🚐 UAZ 469/3151 (front panel)
• 🚖 Mosvich 2141/2138 (rear shelf)
• 🚙 Volkswagen Passat B3/B4 (rear doors, option)
• 🚗 Opel Vectra A (front doors, rare configurations)

In most modern foreign cars (for example, Toyota Corolla, Hyundai Solaris) standard sizes are used: 6.5" or 6×9". If you want to put 20 cm speakers in such a car, you will need:

1. Make adapter rings (adapters) made of plastic or metal.
2. Enlarge the hole with step drill (risk of damage to the door!).
3. Transfer speakers to rear shelf (cabling will be required).

What happens if you install a larger speaker without modifications?

If the speaker is even 0.5 cm wider than the seat, it will not fit tightly, which will lead to:

- body vibrations during loud music,

- sound distortion at low frequencies,

- risk of damage to the diffuser when driving over uneven surfaces.

In the worst case, the speaker could fall out of the hole or damage the door trim.

Top 5 7.9" (20 cm) speakers for cars: characteristics and prices

If your car supports the size 7.9", here are proven models with a good price/quality ratio:

Model	Power (RMS)	Sensitivity (dB)	Price (2026)	Features
Morele.MB Quart DSC-200	100 W	92 dB	~3 500 ₽	Aluminum diffuser, moisture resistant
Prology AC-200	80 W	90 dB	~2 800 ₽	Budget option, suitable for Niva
Alpine SPS-200	120 W	93 dB	~5 200 ₽	Premium segment, Kevlar woofer

⚠️ Attention: When choosing, pay attention to installation depth (mounting depth). For example, in VAZ 2121 The maximum depth of the front speakers is 6 cm, otherwise they will rest against the window lifter. Check this parameter in the car manual or with the seller.

If you plan to amplify the sound with a subwoofer, take speakers with sensitivity from 90 dB — they are better revealed in conjunction with an external amplifier.

Bore diameter (measure with a caliper)

Installation depth (so as not to interfere with the door mechanisms)

RMS power (must match the radio power)

Resistance (4 or 2 ohms - see the car manual)

Availability of adapter rings included-->

Typical mistakes when replacing 20 cm speakers

Even experienced car owners make mistakes that spoil the sound or lead to breakdowns. Here are the most common:

1. Ignoring polarity. If you confuse “+” and “–” when connecting, the speakers will work out of phase: the bass will be “smeared out” and the volume will drop by 30–40%. Always check the markings on the terminals!
2. Saving on sound insulation. Without door vibration insulation (for example, Splen or Bitoplast) the speakers will “buzz” at mid frequencies rather than play clearly.
3. Incorrect power selection. If the radio outputs 50 watts per channel and the speakers are rated at 100 watts, the sound will be distorted at maximum volume.

Critical error: using speakers with an impedance of 2 ohms in a standard radio designed for 4 ohms. This leads to overheating of the amplifier and its failure within 1–2 months.

To avoid problems, follow a simple rule:

The speaker power (RMS) should be 10–20% higher, than the power of the amplifier (or radio output), and the resistance - coincide (usually 4 ohms).

How to modify a seat for 20 cm speakers

If your car has a hole smaller than 20 cm, but you want to install speakers of this size, there are three ways to modify it:

• 🔨 Metal boring. Suitable for cars with thick doors (for example, UAZ, GAZelle). Use a step drill and a grinder with a cutting wheel. Important: After boring, treat the edges with anti-corrosion agent!
• 📏 Adapter rings. Can be ordered from a turner or cut from sheet plastic (thickness 5–8 mm). The ring is attached to self-tapping screws between the speaker and the door.
• 🔧 Transfer to rear shelf. Relevant for sedans. You will need to run the wires from the radio and ensure a tight seal (so that there is no whistling at speed).

Example of modification for VAZ 2114:

1. Remove the door trim.
2. Mark a new hole (diameter 18.5 cm) according to the template.
3. Cut with a grinder, clean the edges with a file.
4. Place the speaker on the soundproofing pad.

Cost of improvement in the service:

• Boring of holes - from RUB 1,500 per door.
• Manufacturing of adapter rings - 800–1,200 RUR.
• Laying wires - 1,000–1,500 RUR.

Frequently asked questions about 20cm speakers

Is it possible to install 8-inch speakers instead of 20 cm ones?

Theoretically yes, but with reservations:

• Physical diameter 8" - 20.32 cm, so they may not fit into the 20 cm hole.
• Bore diameter 8" speakers are often 18.5–19 cm, which may be less than standard.
• Adapter rings or hole rework will be required.

Before purchasing necessarily check the compatibility chart or measure the seat.

Which speakers are better for bass: 6.5" or 20 cm?

A larger diameter (20 cm) is physically capable of reproducing lower frequencies, but it all depends on the design:

• Speakers 6.5" with a good magnet (eg Focal Access 165A1) can play bass better than cheap ones 20 cm.
• For deep bass you need subwoofer - no coaxial speaker can replace it.
• In a closed space door 20 cm Speakers may drone without soundproofing.

Best option for bass: 6.5" component system + subwoofer.

Which magnet is better: ferrite or neodymium?

Comparison:

Parameter	Ferrite magnet	Neodymium magnet
Weight	Heavy	Light (3–5 times)
Cost	Low	High
Sound quality	Good (mid frequencies)	Excellent (clear highs)

For 20 cm For speakers, ferrite magnets are preferable - they are cheaper and more reliable in vibration conditions (relevant for SUVs).

Do I need to change wires when installing new speakers?

Yes, if:

• Old wires are oxidized or have damaged insulation.
• The power of the new speakers is above 80 W (you need a cable with a cross-section of 1.5 mm²).
• You are installing a component system (you will need separate routing for the tweeter and woofer).

For 20 cm For speakers, a standard cable from the radio is sufficient, if its cross-section is not less than 1 mm².

Can 20cm speakers be installed in the rear parcel shelf?

Yes, but consider the nuances:

• The shelf must be rigid (for example, in VAZ 2107 it will have to be reinforced with plywood).
• The speakers should not block the view through the rear window (Traffic Regulations, clause 7.3).
• The holes will need to be sealed, otherwise there will be a whistle at speeds > 80 km/h.

Best used for rear shelf oval speakers (for example, 6×9"), if space allows.