Rope Length Checker
Check whether your rope is long enough to lower or rappel off a route, or see the longest route your rope can handle.
Always tie a stopper knot in the free end of the rope before you lower or rappel. Getting lowered off the end of a rope is one of the most common, most avoidable climbing accidents. Rope stretch and a wandering route eat into your margin, so when a topo says the pitch is 35 m, believe it and do this math before you leave the ground, not halfway down.
This is a planning check, not a substitute for reading the actual topo, inspecting your rope, and confirming rope length with your partner at the anchor.
How it works
Lowering or rappelling off a single-pitch route takes rope on both sides of the anchor, so you need roughly double the route height, plus a margin for stretch, rope drag around a wandering line, and simple error. The calculator uses 2 × route height + margin to answer "how much rope do I need," and the reverse formula, (rope length − margin) ÷ 2, to answer "how tall a route can this rope handle."
Worked example: a 35 m sport route with the default 5 m margin needs 75 m of rope, which rules out a 70 m rope and calls for an 80 m rope instead. Flip it around: a 70 m rope with that same 5 m margin can safely lower or rappel a route up to 32.5 m, and a 60 m rope tops out at 27.5 m. That last one matters, because 60 m used to be the standard length and a lot of older or budget ropes are still that length, while many modern sport routes are bolted for 70 m or even 80 m ropes.
FAQ
Why not just use exactly double the route height?
Dynamic ropes stretch under load, routes rarely run in a perfectly straight line, and knots, rope diameter, and how carefully you counted the pitch all eat into the number. The margin (5 m by default) is there so a small miscount or extra stretch doesn't put you short. On a route you don't know well, or in wet or windy conditions, use a bigger margin, not a smaller one.
What if the topo doesn't list the route height?
Ask at the local gym or crag guidebook, or ask another party who has done the route. If nobody can confirm it, treat the route as taller than you think and rope up conservatively, or lead with a plan to build an intermediate anchor rather than assume a single rappel gets you down.
Does rope diameter or age change this math?
Not the core formula, but a well-used rope stretches more and a skinny rope can run faster through a belay device, so treat an older or thinner rope as needing a bigger margin. Inspect your rope for flat spots, fuzzing, or a soft core before you trust it on a big rappel.
What actually happens if the rope is too short?
The most common failure is getting lowered or rappelling straight off the free end, which is one of the most frequent, most preventable accidents in climbing. A stopper knot in the end of the rope turns a length miscalculation into an awkward stop instead of a fall.
For the hands-on skills behind this check, see how to belay: a beginner's introduction, belay devices explained, and the buddy check.