{"id":5319,"date":"2026-08-18T16:09:37","date_gmt":"2026-08-18T16:09:37","guid":{"rendered":"https:\/\/faradyi.com\/?p=5319"},"modified":"2026-08-18T16:09:43","modified_gmt":"2026-08-18T16:09:43","slug":"what-is-kv-in-brushless-motor-formula-torque-and-selection-guide","status":"publish","type":"post","link":"https:\/\/faradyi.com\/ko\/what-is-kv-in-brushless-motor-formula-torque-and-selection-guide\/","title":{"rendered":"What Is Kv in Brushless Motor? Formula, Torque, and Selection Guide"},"content":{"rendered":"
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What is Kv in a brushless motor?<\/strong> Kv is the motor’s speed constant, commonly expressed in revolutions per minute per volt (RPM\/V). A 1000 Kv motor has an ideal no-load speed tendency of approximately 1,000 RPM for each volt at the motor under the specified measurement convention. Kv does not mean kilovolts, and it is not a direct rating of power, torque, thrust, or efficiency.<\/p>\n

Quick answer:<\/strong> Estimate ideal no-load speed with RPM \u2248 Kv \u00d7 voltage<\/strong>. For example, a 1000 Kv motor at 12 V has an ideal no-load estimate of about 12,000 RPM. Actual speed under load will be lower, and safe motor selection also requires current, torque, power, cooling, ESC, mechanical load, and maximum-speed data.<\/div>\n

What Is Kv in Brushless Motor Specifications?<\/h2>\n

The letter K<\/em> indicates a constant, while the subscript v<\/em> refers to velocity or speed. Product listings often write it as \u201cKV,\u201d but it should not be confused with \u201ckV,\u201d the SI abbreviation for kilovolt.<\/p>\n

In motor theory, the speed constant relates rotational speed to back electromotive force (back EMF). In many hobby and propulsion catalogs, Kv is presented as an approximate no-load RPM per volt. Manufacturers may use different test and waveform conventions, so compare values only when their definitions are compatible.<\/p>\n

Basic Kv formula<\/h3>\n
Ideal no-load RPM \u2248 motor Kv (RPM\/V) \u00d7 voltage at the motor (V)<\/strong><\/div>\n

The equation is a first-pass estimate\u2014not a rated operating point. It does not account for winding voltage drop, controller losses, power-source sag, bearing and windage losses, commutation timing, field weakening, or load torque.<\/p>\n

Brushless Motor Kv Examples<\/h2>\n
\n\n\n\n\n\n\n\n\n
Motor Kv<\/th>\nVoltage used for example<\/th>\nIdeal no-load estimate<\/th>\nWhat it does not prove<\/th>\n<\/tr>\n<\/thead>\n
100 Kv<\/td>\n24 V<\/td>\n2,400 RPM<\/td>\nAvailable loaded torque or continuous power<\/td>\n<\/tr>\n
500 Kv<\/td>\n12 V<\/td>\n6,000 RPM<\/td>\nActual shaft speed with a propeller or gearbox<\/td>\n<\/tr>\n
900 Kv<\/td>\n12 V<\/td>\n10,800 RPM<\/td>\nThrust, efficiency, or a safe propeller size<\/td>\n<\/tr>\n
1500 Kv<\/td>\n12 V<\/td>\n18,000 RPM<\/td>\nMaximum mechanical RPM or ESC suitability<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

On a phone, swipe the table horizontally to view every column.<\/em><\/p>\n

Use the actual voltage available at the motor or controller for engineering calculations. Battery \u201cnominal voltage,\u201d fully charged voltage, and loaded voltage can differ. Confirm the manufacturer’s Kv definition and operating limits.<\/p>\n

Why Actual Loaded RPM Is Lower<\/h2>\n

A rotating permanent-magnet motor generates back EMF that opposes the applied voltage. To produce torque, current must flow through winding resistance and inductance, which requires voltage headroom. As mechanical load increases, the motor draws more phase current and speed settles below the ideal Kv calculation.<\/p>\n

Real speed is affected by:<\/p>\n