Calculate wire size and safety factors for your sailboat's standing rigging
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Download NowStanding rigging is the structure that holds the mast up and lets the sails do their work, and its design is a chain of loads: the wind on the sails becomes a heeling moment, the moment becomes shroud and stay tension, and those tensions add into the compression the mast and its step must bear. Size any link to the everyday breeze and it fails in the gust that matters.
The stays and shrouds each see a different share. The windward shroud takes the heeling load scaled by its angle, the forestay carries headsail and masthead rig tension, and the backstay both supports and tunes the rig, while all of their vertical components stack as mast compression down through the step.
Enter sail area, mast height, shroud angle and design wind, and the calculator estimates heeling moment, shroud, forestay and backstay tensions, total mast compression, and recommends wire sizes with a proper safety factor.
Heeling Moment = Sail Force × CE; Shroud Tension = (Moment ÷ (H × sin Angle)) × 0.5; Compression = Forestay + Backstay + 2 × Shroud| Wire Diameter | Breaking Load | Typical Use |
|---|---|---|
| 5/32 in | 2,500 lb | Small day-sailers |
| 3/16 in | 3,700 lb | Light cruisers |
| 7/32 in | 5,000 lb | Mid cruisers, coastal |
| 1/4 in | 6,400 lb | Offshore and heavy boats |
| 5/16 in | 10,000 lb | Large cruising yachts |
| 3/8 in | 14,400 lb | Heavy and bluewater rigs |
Stainless 1x19 wire rope breaking loads.
Formula verified against standard naval-architecture references · Updated October 2026
Choose wire whose breaking load exceeds the calculated shroud or stay tension with a rigging safety factor of about three to four. The table lists 1x19 stainless breaking loads from 5/32 inch to 3/8 inch, so a mid-size cruiser often lands on 7/32 or 1/4 inch for shrouds. Enter your rig's sail area, height, angle and design wind and the calculator recommends the gauge for each leg with margin built in.
Take the heeling moment from wind pressure on the sails and divide it by the shroud's effective lever, which is the mast height times the sine of the shroud angle, sharing the load with the other side. Because the angle is shallow, the resulting wire tension is a large multiple of the heeling force, and its vertical component adds to compression. That is why shroud angle is one of the most important inputs to the whole rig.
Because every rigging load with a shallow angle to the mast has a large vertical component, and the forestay, backstay and windward shroud all push down at once. Total compression can be several times the side force that caused it, which is why the mast, its step and the structure beneath must be designed for it. This calculator sums the stay and shroud verticals to show the compression you must carry.
Standing rigging is typically designed to a breaking load three to four times the expected maximum working load, reflecting fatigue, corrosion, gust uncertainty and the consequences of failure aloft. That margin is not waste; it is the difference between a rig that survives years of cycling and one that fails at a terminal. Apply it consistently to wire, toggles, clevises and chainplates alike.
On a schedule and by inspection, not by waiting for visible damage. Many insurers and riggers suggest a full replacement of wire rigging around every ten to fifteen years of cruising use, with annual inspection of terminals, swages, chainplates and the waterline areas where crevice corrosion hides. Fatigue and corrosion fail rigging from within, so age and close inspection govern, not appearance.
Not necessarily. In a masthead rig the forestay carries heavy headsail and stay tension and is often sized like the shrouds or larger, while the backstay may be lighter but critical for tune and gust control. A running backstay or checkstay changes the picture. Size each leg to its own computed load and safety factor rather than assuming uniform wire.
Yes, and it is one of the most effective changes you can make. A wider base steepens the shroud angle, which cuts the wire tension and mast compression needed to resist the same heeling moment, letting you carry lighter wire or the same wire with more margin. Longer spreaders, wider chainplates or a wider rig all trade a little deck space for meaningfully lower loads.