Winch Capacity Calculator (Rated Pull, Snatch Block & Line Layers)

How it works

pull needed = weight × (surface factor + sin slope) · winch rating: 1.5 × GVW minimum · layer factor ≈ 100 / 87 / 77 / 69 / 62% for layers 1–5 · snatch block: × 2 (double line) − ~10% friction; line speed halves

A winch's advertised pull is what it manages on the first layer of rope, where the drum radius is smallest and the motor's leverage greatest; each layer wound on top increases the radius and cuts the pull by ten to fifteen percent, so a winch with most of its rope still on the drum is working at little more than half its rating. Against that, the force needed to move a stuck vehicle is a fraction of its weight that grows from a few percent on hard ground to the whole weight in a bog, plus the component of gravity on any slope. The 1.5-times-weight rule of thumb keeps the two in balance for typical recoveries, and a snatch block doubles the effective pull — at half the speed — when they are not.

Worked example

A 2,600 kg loaded 4×4 axle-deep in mud on a 15° slope needs about 2,600 × (0.5 + 0.26) ≈ 1,970 kg — 4,350 lb — of pull. A 12,000 lb winch on its third rope layer delivers about 9,240 lb, more than double what is needed on a single line; the 1.5 × GVW rule calls for at least 8,600 lb, so the winch is properly sized. In a frame-deep bog on the same slope (7,200 lb needed) the third-layer pull is still enough, but a double line would halve the strain and heat.

Frequently asked questions