Elevator Rope Calculator
Rope count, diameter, and safety factor.
About this calculator
This calculator sizes the wire-rope suspension for a traction elevator: how many ropes are needed, and how much margin they carry above the ASME A17.1 minimum safety factor of 8.0. Breaking Strength/Rope depends only on Rope Diameter and Rope Grade (IPS, EIPS, or EEIPS) -- it is a per-rope material property, unaffected by how heavy the car or load is. Number of Ropes Required divides the total suspended load (car weight + rated load, times the Required Safety Factor) by that per-rope strength and rounds up, with a hard 3-rope ASME minimum -- so a larger Rope Diameter needs fewer, stronger ropes to hit the same total strength, in coarse steps rather than a smooth curve, because ropes only come in whole units -- there's no such thing as a fractional rope.
Min Sheave Diameter is a straight multiple of Rope Diameter (the code's D/d >= 40 ratio) and has nothing to do with rope grade, car weight, or travel height. Total Rope Length adds up travel height, a machine-room overhead allowance, and pit allowance for every rope, so a longer Travel Height raises both the length per rope AND, indirectly through added compensation-rope weight, the number of ropes needed -- both factors push Total Rope Length up together as travel increases.
Inputs
Results
Number of ropes required
6
Figures current as of 2004. Source: ASME A17.1, Safety Code for Elevators and Escalators, Section 2.20-2.24 (Suspension Means)
How to Use This Calculator
- Enter Car weight (kg), Rated load (kg), and Travel height (m).
- Set Rope diameter (mm), Rope grade (1=IPS, 2=EIPS, 3=EEIPS), and Required safety factor.
- Review the Number of ropes required result.
- Use Actual safety factor and Breaking strength/rope (kN) to inform your decision.
How the result changes with Rope diameter (mm)
| Rope diameter (mm) | Number of ropes required |
|---|---|
| 6 | 23 |
| 9 | 10 |
| 18 | 3 |
| 25 | 3 |
What each input means
- Car weight (kg)
- Weight of the empty elevator car including platform and sling.
- Rated load (kg)
- Maximum passenger/freight load. 1 person ≈ 75 kg.
- Travel height (m)
- Total vertical travel distance from lowest to highest landing.
- Rope diameter (mm)
- Wire rope diameter. Common sizes: 8, 10, 12, 16 mm.
- Rope grade (1=IPS, 2=EIPS, 3=EEIPS)
- Wire rope grade: 1 = Improved Plow Steel, 2 = Extra Improved, 3 = Extra Extra Improved.
- Required safety factor
- Minimum safety factor per ASME A17.1 (≥ 8.0 for traction elevators).
What each result means
- Number of ropes required
- Minimum number of wire ropes needed (ASME minimum: 3).
- Actual safety factor
- Achieved safety factor with the selected number of ropes.
- Breaking strength/rope (kN)
- Minimum breaking strength of each rope based on diameter and grade.
- Total rope length (m)
- Total length of all ropes including overhead and pit allowances.
- Total rope weight (kg)
- Combined weight of all suspension ropes.
- Weight per meter (kg/m)
- Linear weight of one rope.
- Min sheave diameter (mm)
- Minimum traction sheave diameter based on D/d ≥ 40 ratio.
- Total suspended load (kg)
- Combined car weight, rated load, and compensation.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersCar weight (kg) = 2500, Rated load (kg) = 1600, Travel height (m) = 30, Rope diameter (mm) = 12 = 6 input(s) provided
- Calculate Number of ropes requiredNumber of ropes required = max(3, ceil(numRopesExact))6 = 6
- Calculate Actual safety factorActual safety factor = (numRopes * breakingStrengthKN) / totalLoadKN8.63 = 8.63
- Calculate Breaking strength/ropeBreaking strength/rope = 0.36 * d * d * gradeFactor / 1058.1 = 58.1
Figures and sources
- ASME A17.1 traction elevator suspension-means requirements: minimum safety factor 8.0, minimum 3 ropes, D/d ≥ 40 sheave-to-rope diameter ratio (2004) — ASME A17.1, Safety Code for Elevators and Escalators, Section 2.20-2.24 (Suspension Means)
Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Does a heavier car or rated load change the Breaking Strength/Rope?
No. Breaking Strength/Rope is a property of the rope itself -- diameter and grade only -- computed the same way regardless of Car Weight or Rated Load. A heavier car or load only changes Number of Ropes Required and Actual Safety Factor, by raising the total strength needed, never the strength any single rope can provide.
Why did increasing the rope diameter slightly not reduce the rope count?
Number of Ropes Required rounds UP to a whole rope, so a small diameter increase only reduces the count once the extra per-rope strength is enough to actually drop below the next whole-rope threshold. Across the full 6-25mm declared range the count is never higher for a bigger diameter, but between threshold crossings it can hold flat at the ASME 3-rope minimum or any intermediate count.
What determines the Min Sheave Diameter, and does rope grade matter for it?
Min Sheave Diameter is simply 40 times the Rope Diameter, following ASME A17.1's minimum D/d (sheave-to-rope diameter) ratio for traction elevators -- it rises in direct proportion to Rope Diameter and is completely unaffected by Rope Grade, since grade only changes a rope's breaking strength, not its physical diameter.
How does Travel Height affect the total rope length needed?
Total Rope Length increases with Travel Height through two combined effects: each individual rope gets longer (travel plus a machine-room overhead allowance and pit allowance, both scaled to travel), and the compensation-rope weight added to the total suspended load can push Number of Ropes Required up a step -- both effects move in the same direction, so total rope length rises monotonically across the full 1-500m travel range.
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