How to Calculate Electric Hoist Wire Rope Length (Formula & Example)
Core Formula: Electric hoist wire rope length L = H × n + L₁. Here, H is the lifting height, n is the hoisting reeving, and L₁ is the reserved length for safety wraps on the drum (approx. 3–5 m). Per ISO 4301, the number of safety wraps remaining on the drum must be no fewer than 3.
One of the most common questions when replacing the wire rope on an electric hoist is how to determine the correct length. Buy too short, and the hoist won't reach the required lifting height. Buy too long, and you're wasting money on rope that has to be cut off and discarded. As a wear part, the wire rope on an electric hoist is a consumable item that must be replaced periodically. Getting the length right ensures both safe operation and controlled maintenance costs. As the technical manager at Kelude puts it: "Keeping the wire rope length within ±0.5 m meets all safety requirements while avoiding unnecessary material waste."
This article covers the wire rope length calculation formula for electric hoists, explains each parameter in detail, provides a quick reference table for common capacity × height combinations, and lists key precautions to keep in mind when purchasing replacement rope — so you can get it right the first time.
How Do You Calculate Electric Hoist Wire Rope Length?
A: The total wire rope length is calculated using the formula L = H × n + L₁, where H is the maximum lifting height (m), n is the hoisting reeving, and L₁ is the reserved length for safety wraps on the drum (approx. 3–5 m). For example, a CD1 5t hoist with a 12 m lifting height, reeving of 2, and a 180 mm drum diameter gives L = 12 × 2 + 3 × π × 0.18 ≈ 26 m. See the detailed calculation method and quick reference table above.
Electric Hoist Wire Rope Length Calculation Formula
The standard formula for calculating the total wire rope length of an electric hoist is:
L = H × n + L₁
Each parameter is defined as follows:
L — Total wire rope length, in meters (m);
H — Maximum lifting height, in meters. Standard lifting heights for CD1/MD1 electric hoists are 6 m, 9 m, 12 m, 18 m, 24 m, and 30 m; custom heights are available on request;
n — Hoisting reeving. The number of times the wire rope is reeved between the movable and fixed pulley blocks, typically 2 or 4 depending on the hoist capacity. A higher reeving ratio reduces the load on each rope but correspondingly lowers the lifting speed;
L₁ — Reserved length for safety wraps on the drum, approximately 3–5 m. Per ISO 4301 Crane Design Standard, the number of safety wraps remaining on the drum must be no fewer than 3 (wraps used for rope end termination are not counted), ensuring reliable rope end fixing and preventing the wire rope from completely unwinding off the drum. Kelude typically allows for 3–5 wraps in production to maintain an adequate safety margin.
Parameter Breakdown for Wire Rope Length
2.1 Hoisting Reeving vs. Hoist Capacity
The hoisting reeving is the number of times the wire rope is reeved through the pulley block, and it directly determines how much rope is needed for a given lifting height. The table below shows the standard reeving ratios for common CD1/MD1 electric hoist capacities:
Kelude Heavy Industry is a professional manufacturer of industrial cranes and hoists, integrating design, production, sales, and service. Our product lineup covers a wide range of material handling equipment, including single-girder and double-girder overhead cranes, gantry cranes, and electric wire rope hoists, among others. These products are widely used in machinery manufacturing, metallurgy, petrochemicals, new energy, and other industries, delivering efficient and reliable lifting solutions for customers.
| Capacity(t) | Commonhoisting reeving | drum diameter(mm) | Length per Revolution(m) |
|---|---|---|---|
| 0.5 | 2(or1) | 140 | 0.44 |
| 1 | 2 | 140 | 0.44 |
| 2 | 2 | 140 | 0.44 |
| 3 | 2 | 160 | 0.50 |
| 5 | 2 | 180 | 0.57 |
| 8 | 4 | 200 | 0.63 |
| 10 | 4 | 220 | 0.69 |
| 16 | 4 | 300 | 0.94 |
| 20 | 4 | 300 | 0.94 |
Note: Drum diameter may vary slightly by manufacturer and production batch; the values above are typical for the CD1 series. Circumference per wrap = π × D, using π ≈ 3.14.
2.2 Safety Wraps on the Drum
Safety wraps are a critical yet often overlooked factor when calculating wire rope length. Per Clause 6.2.3 of ISO 4301 Crane Design Standard, when the hook is at its lowest working position, each wire rope on the drum must retain no fewer than 3 wraps (excluding the wraps securing the rope end). This prevents the rope end termination from bearing direct tensile load and coming loose, ensuring reliable rope end fixing. In practice, Kelude typically reserves the following wraps on CD1/MD1 Electric Hoists:
① Small tonnage (≤5t) — 3 wraps, approximately 1.3–1.7 m;
② Medium tonnage (8–10t) — 4 wraps, approximately 2.5–2.8 m;
③ Large tonnage (16–20t) — 4 wraps, approximately 3.8 m.
It is important to note that the fleet angle of the wire rope on the drum (the included angle between the rope centerline and the plane perpendicular to the drum groove) must not exceed 3.5°. Exceeding this limit can cause uneven rope spooling, accelerate wear, and in severe cases lead to rope crossover or jumping off the groove.
3. Wire Rope Length Quick Reference Table
The table below lists the overall wire rope length required for each common CD1 Electric Hoist tonnage at various Lifting Heights, with safety wraps already included. Use it for direct reference.
| Capacity(t) | Pulley Ratio | 6m | 9m | 12m | 18m | 24m | 30m |
|---|---|---|---|---|---|---|---|
| 0.5 | 2 | 13 | 19 | 25 | 37 | 49 | 61 |
| 1 | 2 | 13 | 19 | 25 | 37 | 49 | 61 |
| 2 | 2 | 13 | 19 | 25 | 37 | 49 | 61 |
| 3 | 2 | 14 | 20 | 26 | 38 | 50 | 62 |
| 5 | 2 | 14 | 20 | 26 | 38 | 50 | 62 |
| 8 | 4 | 27 | 39 | 51 | 75 | 99 | 123 |
| 10 | 4 | 27 | 39 | 51 | 75 | 99 | 123 |
| 16 | 4 | 28 | 40 | 52 | 76 | 100 | 124 |
| 20 | 4 | 28 | 40 | 52 | 76 | 100 | 124 |
Note: Values in the table are rounded up to the nearest whole meter. It is recommended to add 1–2 m of extra allowance to the calculated value when purchasing. Drum diameters may vary slightly between manufacturers; always refer to the product manual for exact specifications.
4. Calculation Examples
The following three worked examples demonstrate how to apply the formula in practice.
Example 1: CD1 5t, Lifting Height 12m
Given: H = 12m, n = 2 (pulley ratio for 5t), drum diameter D = 180mm (0.18m), safety wraps = 3
L = H × n + 3 × π × D = 12 × 2 + 3 × 3.14 × 0.18 = 24 + 1.70 = ≈26m
Result: The total wire rope length required for the CD1 5t/12m electric hoist is approximately 26m. It is recommended to order 28m to allow for fitting and future re-termination.
Example 2: CD1 10t, Lifting Height 18m
Given: H = 18m, n = 4 (pulley ratio for 10t), drum diameter D = 220mm (0.22m), safety wraps = 4
L = H × n + 4 × π × D = 18 × 4 + 4 × 3.14 × 0.22 = 72 + 2.76 = ≈75m
Result: The total wire rope length required for the CD1 10t/18m electric hoist is approximately 75m. It is recommended to order 78m to allow for fitting and future re-termination.
Example 3: CD1 2t, Lifting Height 9m
Given: H = 9m, n = 2 (pulley ratio for 2t), drum diameter D = 140mm (0.14m), safety wraps = 3
L = H × n + 3 × π × D = 9 × 2 + 3 × 3.14 × 0.14 = 18 + 1.32 = ≈19m
Result: The total wire rope length required for the CD1 2t/9m electric hoist is approximately 19m. It is recommended to order 21m to allow for fitting and future re-termination.
5. Key Precautions When Buying Wire Rope
Beyond calculating the correct length, keep the following critical points in mind when purchasing wire rope for an electric hoist:
①Allow extra length — Add 1–2 m of extra allowance to the calculated length. This extra length is needed for cutting, fixing, and splicing at the rope end, and it also allows the rope end to be cut off and re-terminated later when worn, extending the overall service life.
②Use one continuous rope — never splice — The wire rope for an electric hoist must be a single, continuous length. Never join multiple sections using rope clamps or splicing. The tensile strength at a spliced joint is only 60%–80% of the original rope, and the joint causes severe bouncing as it passes over the drum, which can lead to rope breakage in serious cases.
③Match the wire rope construction — The CD1 electric hoist typically uses a 6×37+FC wire rope construction (6 strands, 37 wires per strand, fiber core) with a tensile strength of ≥1570MPa. Different rope constructions offer different levels of toughness and fatigue resistance, so always replace with the same construction as the original rope.
④Confirm the wire rope diameter — Electric hoists of different capacities use wire ropes of different diameters. A 0.5t hoist uses 5–7 mm rope, a 5t hoist uses 11–13 mm, a 10t hoist uses 15–17 mm, and a 16–20t hoist uses 18–20 mm. If the rope is too thick, it won't seat properly in the rope groove; if too thin, it will shift around in the groove and accelerate wear.
⑤Rigging screw orientation — When replacing the wire rope, pay attention to the reeving direction and the mounting orientation of the hook block to ensure the rope spools evenly on the drum, with the fleet angle kept within 3.5°. Kelude Heavy Industry includes a detailed reeving diagram in the factory manual for the CD1 electric hoist; we recommend reviewing the diagram to confirm the rope path before starting the replacement.
FAQ
Q: How do I calculate the wire rope length for a 10t electric hoist?
A: The 10t electric hoist has a hoisting reeving of 4 and a drum diameter of approximately 220 mm. Using a standard lifting height of 12 m as an example: L = 12 × 4 + 4 × π × 0.22 = 48 + 2.76 ≈ 51 m. Simply substitute your actual lifting height into the formula. We recommend adding 1–2 m of extra rope when ordering, so plan for 53–54 m.
Q: How many meters of wire rope do I need for a 2t, 9 m electric hoist?
A: The 2t electric hoist has a hoisting reeving of 2 and a drum diameter of approximately 140 mm. With 3 safety wraps on the drum: L = 9 × 2 + 3 × π × 0.14 = 18 + 1.32 ≈ 19 m. Add a margin and order 21 m. Note that the wire rope diameter for a 2t electric hoist is typically 7–9 mm (6×37+FC construction).
Q: How many wraps of wire rope remain on a 5t electric hoist drum?
A: Per ISO 4301 Crane Design Standard, the drum must retain at least 3 wraps of wire rope (excluding the wraps securing the rope end). The 5t electric hoist has a drum diameter of approximately 180 mm, so 3 wraps correspond to about 1.7 m of rope. In production, Kelude Heavy Industry leaves 3–5 safety wraps at each end of the drum to ensure sufficient wraps remain to secure the rope end when the hook is at its lowest position.
Q: How many meters of wire rope does a 16t electric hoist need?
A: The 16t electric hoist has a hoisting reeving of 4 and a drum diameter of approximately 300 mm. Using an 18 m lifting height as an example: L = 18 × 4 + 4 × π × 0.30 = 72 + 3.77 ≈ 76 m. The wire rope diameter for a 16t electric hoist is typically 18–20 mm (6×37+FC construction). We recommend ordering 78–80 m and confirming the rope's tensile strength is ≥1570 MPa.
Related reading:
• CD1/MD1 Wire Rope Electric Hoist — Models, Parameters, Pricing & Selection by Capacity — Full technical specifications for electric hoists across all capacities
• 5t Electric Hoist Technical Parameters & Selection Guide: Wire Rope Specs, I-Beam Rail, Motor Power, Pricing — Detailed configuration reference for the 5t electric hoist
