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Speedometer vs. Tachometer — What's the Difference?

By Tayyaba Rehman — Updated on October 24, 2023
A "speedometer" measures a vehicle's speed, usually in mph or km/h, while a "tachometer" indicates engine revolutions, often in RPM.
Speedometer vs. Tachometer — What's the Difference?

Difference Between Speedometer and Tachometer


Key Differences

"Speedometer" and "tachometer" are both crucial instruments found in vehicles, but they measure different aspects. A "speedometer" provides the driver with a real-time reading of the vehicle's speed. Whether you're driving a car, motorcycle, or truck, the speedometer aids in ensuring you're within legal and safe limits. The unit of measure is typically miles per hour (mph) in the U.S. or kilometers per hour (km/h) elsewhere.
On the contrary, a "tachometer" focuses on the engine's performance. It tracks the number of rotations the engine's crankshaft makes per minute, abbreviated as RPM (revolutions per minute). While the "speedometer" relates to the vehicle's movement, the "tachometer" offers insights into engine health and efficiency. A consistently high RPM reading, for instance, may suggest the engine is working too hard.
The essence of a "speedometer" is to offer information pertinent to road safety and traffic rules. As you speed up or slow down, the needle or digital reading adjusts accordingly, assisting drivers in adapting to speed regulations. Conversely, a "tachometer" doesn't directly link to speed. Instead, it gives drivers an understanding of when to shift gears in manual vehicles or alerts to potential engine issues.
To summarize, while both instruments are dashboard staples, they serve distinct functions. The "speedometer" is all about velocity, aiding drivers in adhering to speed limits. The "tachometer", meanwhile, revolves around the engine, guiding optimal gear shifts and highlighting potential engine concerns.

Comparison Chart


Measures vehicle speed.
Measures engine revolutions.

Typical Unit

MPH (miles per hour) or km/h (kilometers per hour).
RPM (revolutions per minute).


Pertains to vehicle's movement on a road.
Relates to engine's internal performance.


Helps adhere to speed limits.
Indicates when to shift gears; flags potential engine issues.


Found on all road vehicles' dashboards.
Common in cars, especially with manual transmissions.

Compare with Definitions


An instrument indicating vehicle speed.
The speedometer showed I was going 55 mph.


An instrument measuring engine revolutions.
The tachometer was hovering around 3,000 RPM.


Measures speed in mph or km/h.
The speedometer's needle was approaching 70 km/h.


Common in cars, especially manuals.
The car's tachometer had a red zone starting at 7,000 RPM.


Often analog with a needle or digital.
The car's digital speedometer displayed a clear 45.


Displays engine speed in RPM.
As I accelerated, the tachometer needle climbed.


A speedometer or speed meter is a gauge that measures and displays the instantaneous speed of a vehicle. Now universally fitted to motor vehicles, they started to be available as options in the early 20th century, and as standard equipment from about 1910 onwards.


Useful for manual gear shifts.
I shifted gears when the tachometer hit the redline.


An instrument on a vehicle's dashboard indicating its speed.


Can indicate engine health or stress.
The tachometer's high reading suggested the engine was overworking.


An instrument for indicating speed.


A tachometer (revolution-counter, tach, rev-counter, RPM gauge) is an instrument measuring the rotation speed of a shaft or disk, as in a motor or other machine. The device usually displays the revolutions per minute (RPM) on a calibrated analogue dial, but digital displays are increasingly common.


An instrument for indicating distance traveled as well as rate of speed.


An instrument which measures the working speed of an engine (especially in a road vehicle), typically in revolutions per minute.


An odometer.


An instrument used to measure the rotations per minute of a rotating shaft.


An instrument located within the dashboard of a vehicle that measures and indicates the current speed of the vehicle.


A device for measuring the revolutions per minute (RPMs) of a revolving shaft, as with the driveshaft of an automobile.


Such a device incorporating an odometer.


A device for measuring or indicating velocity or speed, as of blood, a river, a machine, etc.


A meter fixed to a vehicle that measures and displays its speed


An instrument for measuring the velocity, or indicating changes in the velocity, of a moving body or substance.


Essential for adhering to speed limits.
I glanced at the speedometer to ensure I wasn't speeding.


An instrument for measuring the velocity of running water in a river or canal, consisting of a wheel with inclined vanes, which is turned by the current. The rotations of the wheel are recorded by clockwork.


Found in every road vehicle's dashboard.
The speedometer's backlight was dim, making it hard to read at night.


An instrument for showing at any moment the speed of a revolving shaft, consisting of a delicate revolving conical pendulum which is driven by the shaft, and the action of which by change of speed moves a pointer which indicates the speed on a graduated dial.


An instrument for measuring the velocity of the blood; a hæmatachometer.


Measuring instrument for indicating speed of rotation

Common Curiosities

Why is a "tachometer" essential in manual cars?

It helps drivers know when to shift gears.

If my "tachometer" consistently reads high, is there a problem?

It might indicate the engine is overworking or there's a need to shift.

Where are these instruments typically located?

Both are found on a vehicle's dashboard.

Can I drive without a functioning "speedometer"?

It's unsafe and potentially illegal to drive without a working speedometer.

Do both "speedometer" and "tachometer" measure speed?

The "speedometer" measures vehicle speed, while the "tachometer" measures engine revolutions.

Why do some vehicles lack a "tachometer"?

Some automatic or simpler vehicles might not have them, as they're more crucial for manual transmissions.

Is it common for both instruments to fail simultaneously?

No, but issues like a blown fuse could affect both.

What unit does a "speedometer" use in the U.S.?

It typically uses miles per hour (mph).

Is it possible for a "speedometer" to show incorrect speeds?

Yes, calibrations or mechanical issues can affect accuracy.

Does a "tachometer" read high in a fast-moving car?

Not necessarily; it reflects engine RPM, not vehicle speed.

Can a "speedometer" be digital?

Yes, modern cars often have digital speedometers.

Why do "tachometers" have a red zone?

It indicates RPM levels that are potentially harmful to the engine.

Why might a racer monitor the "tachometer" closely?

To optimize gear shifts and engine performance during a race.

Can I install an aftermarket "tachometer"?

Yes, especially for vehicles with manual transmissions or for tuning purposes.

Does every vehicle have a "speedometer"?

Virtually all road vehicles have a speedometer for safety and legal reasons.

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Author Spotlight

Written by
Tayyaba Rehman
Tayyaba Rehman is a distinguished writer, currently serving as a primary contributor to As a researcher in semantics and etymology, Tayyaba's passion for the complexity of languages and their distinctions has found a perfect home on the platform. Tayyaba delves into the intricacies of language, distinguishing between commonly confused words and phrases, thereby providing clarity for readers worldwide.

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