Crane Hoist Motor Power Calculator

This free online crane hoist motor power calculator determines the required motor power for overhead crane and gantry crane hoisting mechanisms. Enter the rated lifting capacity, hoisting speed, and mechanical efficiency — and get the calculated motor power in kilowatts instantly.

The calculator is compliant with major international crane design standards including ISO 4301, FEM 1.001 (European crane specifications), and GB/T 3811 (Chinese national standard). It covers duty classes A1–A6 (equivalent to M1–M6) and rated capacities from 0.5 t to 200 t under standard operating conditions.

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Calculation Formula

\[P = \frac{m \cdot g \cdot v}{1000 \cdot \eta}\]

Symbol	Definition	Unit
P	Required hoist motor power	kW
m	Rated lifting mass (safe working load)	kg
g	Gravitational acceleration (9.81)	m/s²
v	Rated hoisting speed	m/s
η	Total mechanical efficiency of the hoist drivetrain	decimal (e.g. 0.85)

Unit conversions applied automatically:

• Lifting capacity entered in tonnes (t) is converted to kg (× 1000)
• Hoisting speed entered in m/min is converted to m/s (÷ 60)

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How to Use the Calculator

Step 1 — Enter Lifting Capacity (tonnes)

Enter the rated lifting capacity (safe working load, SWL) of the crane as specified in the design documentation or on the crane data plate. Do not include the self-weight of the hook block or lifting attachments — the formula uses the net rated load on the hook.

Applicable range: 0.5 t to 200 t

Step 2 — Enter Hoisting Speed (m/min)

Enter the rated hoisting speed in metres per minute. This is the full-load hoisting speed at which the hoist is designed to lift the rated load — not the no-load speed, which is typically 10–20% higher for motors with slip characteristics.

Typical hoisting speeds by application:

التطبيق	Typical Hoisting Speed
Precision assembly, clean rooms	0.5–2 m/min
General workshop overhead cranes	3-8 م/دقيقة
Storage and warehousing	6–12 m/min
Grab bucket or magnet cranes	10-20 م/دقيقة
Port and shipyard cranes	15–30 m/min

Step 3 — Enter Mechanical Efficiency (η)

Mechanical efficiency η represents the ratio of useful output power (lifting the load) to total input power drawn by the motor. The difference is lost to friction in the gearbox, rope reeving system, sheaves, drum bearings, and rope bending. η is entered as a decimal (e.g. 0.85 for 85%).

Typical efficiency values by reeving configuration:

Reeving / Hoist Type	Typical η Range
Single-fall (1/1 reeving), wire rope hoist	0.90–0.95
2-fall reeving	0.87–0.92
4-fall reeving	0.82–0.88
6-fall reeving	0.78–0.85
8-fall reeving	0.75–0.82
Chain hoist (electric)	0.65–0.80

For a complete drivetrain, η is the product of individual component efficiencies: gearbox efficiency (typically 0.92–0.97 per stage), open gear efficiency (0.95–0.97), rope reeving efficiency (0.96–0.98 per sheave), and drum bearing efficiency (0.99). A typical wire rope hoist with 4-fall reeving and a two-stage gearbox produces an overall η of approximately 0.82–0.86.

When η is unknown, use 0.85 as a conservative starting estimate for a standard wire rope hoist with 4-fall reeving.

Step 4 — Read the Result

The calculator returns the calculated required motor power P in kW. This is the theoretical minimum power needed to lift the rated load at the rated speed against friction losses.

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From Calculated Power to Selected Motor Power

The calculated value P is a theoretical minimum. The actual motor selected for the hoist must satisfy several additional requirements beyond the bare formula result.

Standard Motor Power Ratings

Electric motors are manufactured in standardised power ratings. The selected motor must meet or exceed the calculated P, rounded up to the next standard rating. Common IEC standard power ratings (kW) include:

0.37 / 0.55 / 0.75 / 1.1 / 1.5 / 2.2 / 3.0 / 4.0 / 5.5 / 7.5 / 11 / 15 / 18.5 / 22 / 30 / 37 / 45 / 55 / 75 / 90 / 110 / 132 / 160 / 200 / 250 / 315 / 400 / 500

Always select the first standard rating above the calculated P, never round down.

Duty Cycle (Cyclic Duration Factor, CDF / ED%)

Crane hoist motors operate intermittently — they run during the hoisting phase and are idle during load positioning, travel, and unloading. Motor thermal ratings are expressed at a standard cyclic duration factor (CDF or ED%), typically 25%, 40%, or 60% for crane duty.

A motor rated at 15 kW at 40% ED can produce 15 kW continuously during the lifting phase as long as it is not energised more than 40% of the total operating time. Operating the same motor at 60% ED without derating will overheat the windings over time.

Ensure the selected motor's ED% rating matches or exceeds the duty cycle required by the crane's actual operating pattern. For high-cycle cranes (A5–A6 / M5–M6), a 60% ED motor is generally required.

Service Factor for Duty Class

Higher duty class cranes require more frequent starts under full load, which increases thermal loading on the motor beyond what the rated power alone implies. As a practical guide:

Duty Class (ISO/FEM)	Recommended Service Factor on P
A1–A2 (M1–M2)	1.0
A3–A4 (M3–M4)	1.1–1.15
A5–A6 (M5–M6)	1.2–1.25

Multiply the calculated P by the service factor before selecting the standard motor rating for higher-duty applications.

Altitude and Temperature Derating

This calculator assumes standard operating conditions: altitude ≤ 1,000 m above sea level and ambient temperature ≤ 40 °C. Outside these limits, motor output must be derated:

Altitude derating: Above 1,000 m, air density decreases, reducing the motor's cooling capacity. A typical derating of 1% per 100 m above 1,000 m applies (check manufacturer data). At 2,000 m, the motor should be derated by approximately 10%.

Temperature derating: Above 40 °C ambient, the motor's allowable temperature rise above ambient is reduced. A typical derating of 1–2% per degree Celsius above 40 °C applies. At 50 °C ambient, derate by approximately 10–15%.

To account for derating, divide the calculated P by the derating factor before selecting the standard motor size. For example, at 2,000 m altitude with a derating factor of 0.90: select a motor rated at P / 0.90.

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Why Mechanical Efficiency η Matters

The efficiency term η is often underestimated in quick calculations. Its effect on motor size is significant:

η Value	Motor Power for 10 t at 6 m/min
0.95	10.3 kW
0.85	11.5 kW
0.75	13.1 kW
0.65	15.1 kW

The difference between a well-maintained 4-fall reeving system (η ≈ 0.85) and a worn, poorly lubricated chain hoist (η ≈ 0.65) can mean a 30% larger motor requirement for the same lift. Using an overly optimistic η leads to an underpowered motor that overheats under load, trips thermal protection devices, and suffers accelerated insulation degradation.

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Applicable Products and Scope

Applicable Crane Types

• رافعات علوية بعارضة واحدة
• Double girder overhead cranes
• Single girder gantry cranes
• Double girder gantry cranes
• Wire rope electric hoists on standard trolleys

Operating Conditions

المعلمة	Applicable Range
Rated lifting capacity	0.5 t – 200 t
فئة الواجب	A1–A6 (equivalent M1–M6)
Altitude	≤ 1,000 m
Ambient temperature	≤ 40 °C
Working environment	General indoor workshops and outdoor yards
مصدر الطاقة	Stable grid voltage (±10% of nominal)

Not Applicable For

The formula P = m·g·v / (1000·η) is a steady-state hoisting power equation. It does not account for the additional power demands or design constraints of the following special applications, which require separate engineering calculations:

• Foundry cranes (ladle cranes, charging cranes) — radiant heat exposure requires thermally derated motors and enclosures; duty cycles may be extreme
• رافعات مقاومة للانفجار — motor selection is governed by ATEX or IECEx zone classification, temperature class, and enclosure group requirements beyond basic power rating
• Nuclear power cranes — seismic qualification, single-failure-proof design, and nuclear-grade component standards apply
• High-altitude installations (> 1,000 m) — explicit derating calculation required before motor selection
• High-temperature environments (> 40 °C ambient) — explicit derating required
• Cranes with regenerative lowering requirements — where the lowering load is large and speeds are high, a regenerative or braking resistor system may be required and motor selection must consider four-quadrant operation
• Variable-frequency drive (VFD) applications with specific speed ranges — motor-VFD matching and torque-speed curves require analysis beyond the base power formula

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الأسئلة الشائعة

Q1：What is the difference between calculated motor power and rated motor power?

The calculated power P from the formula is the theoretical minimum required to lift the load at rated speed against drivetrain friction. The rated motor power is the standardised value of the selected motor, which must be equal to or greater than P. The selected motor will always be slightly larger than the calculated value because motors only exist in discrete standard ratings, and additional margins for duty class and service factor are applied.

Q2：Should the hook block weight be included in m?

No. The formula uses only the rated lifting capacity (the net load on the hook). The hook block, shackle, slings, and other attachments are part of the crane's fixed equipment and are accounted for in the structural design and wheel load calculations, not in the hoist motor power formula. Motor power is sized to lift the payload, not the crane's own lifting hardware.

Q3：How do I find the mechanical efficiency of my hoist?

For a new hoist, the manufacturer's technical datasheet will state the overall mechanical efficiency or the efficiencies of individual components (gearbox, rope reeving). For an existing hoist where documentation is unavailable, estimate η from the reeving configuration using the typical values in Step 3. For a detailed assessment, measure input power and output (lifting force × speed) directly.

Q4：Can this calculator be used for chain hoists?

Yes, for general power estimation. However, chain hoists have lower mechanical efficiency than wire rope hoists (typically η = 0.65–0.80 for electric chain hoists) due to the higher friction in the chain-and-sprocket system. Use the appropriate η value and note that chain hoists are generally limited to lower capacities and slower speeds than the ranges covered by standard wire rope hoist motor selections.

Q5：What happens if the motor is slightly underpowered?

A motor that is marginally undersized will run hotter than rated temperature during full-load lifts. The thermal protection relay or motor protection circuit breaker will trip when winding temperature exceeds the limit, interrupting the lift. Repeated thermal cycling accelerates insulation degradation and shortens motor life significantly. In severe cases, a continuously undersized motor will fail within months. Always select the next standard rating above the calculated P.

Q6：Does hoisting speed affect motor size more than load capacity?

Both have equal weight in the formula — P is proportional to both m and v. Doubling the load or doubling the speed both double the required power. In practice, speed is often the more flexible variable: specifying a lower hoisting speed (e.g. 3 m/min instead of 6 m/min for the same capacity) halves the required motor power, which can meaningfully reduce hoist weight, cost, and energy consumption for applications where cycle time is not critical.

Q7：How does VFD (variable-frequency drive) control affect motor selection?

A VFD allows the motor to operate across a range of speeds by varying the supply frequency. For hoist applications, VFDs are used to provide smooth start/stop (reducing dynamic loads and rope shock), creep speed for precise load positioning, and sometimes regenerative braking during lowering. The rated power of the motor is still determined by the formula at full rated speed, but the motor frame size may need to be increased if the VFD requires the motor to run below base speed at full torque for extended periods, since self-cooling is reduced at low speeds.