How to Use This SRT Rope Length Calculator
Enter the details for each vertical pitch on your trip. The calculator adds up all the rope you will actually need to rig the pitch safely — not just the raw depth measurement.
- Set global options — choose your rope diameter (8–11 mm) and rigging style (Alpine or American). These apply to all pitches.
- Enter pitch depth — the surveyed or estimated vertical drop from the rigging anchor to the bottom of the pitch.
- Add anchor setback — the distance of rope between your backup/traverse belay and the pitch lip. This rope is consumed but not "in the pit".
- Select Y-hang — if you plan to use a Y-hang at the pitch head, check Yes. This adds ~2 m for the two-leg configuration and knots.
- Count rebelays — each rebelay midway down the pitch consumes about 1 m of rope for the knot and rigging loop.
- Add more pitches — click the + button to add all the pitches on your route. The summary table shows total rope and weight for the trip.
- Print or share — use "Print / Save PDF" to produce a clean packing summary, or copy the URL to share your plan.
Why Raw Depth Is Never Enough
Many cavers have arrived at a pitch head with a rope that is "just too short." The surveyed depth is only part of the story. Before the rope even enters the pit, it must reach from the backup belay to the pitch edge — this traverse/approach section can easily be 2–5 m on wide passage. The Y-hang anchor configuration then consumes another 1–2 m. Each rebelay knot uses roughly 1 m. The bottom safety tail should hang 1–2 m below the lowest point the caver intends to reach. On a pitch with a 3 m setback, a Y-hang, and two rebelays, a 30 m pitch needs approximately 38 m of rope.
Pitch depth: 30 m | Anchor setback: 3 m | Y-hang: yes (+2 m) | Rebelays: 2 (×1 m = +2 m) | Safety margin: 2 m
Total rope = 30 + 3 + 2 + 2 + 2 = 39 m
With 9 mm rope (53 g/m): carry weight = 39 × 53 g = 2.07 kg (this pitch alone)
Alpine vs American SRT
Alpine (European) style uses lighter 8–9 mm rope rigged with multiple rebelays and deviations to keep the rope free-hanging and away from rock contact. The first descent rigs the cave; subsequent cavers pass rebelays. Slower to rig initially, but much faster for groups and kinder to the rope. The default for most European caving regions and deep expedition caving.
American style (IRT — Indestructible Rope Technique) traditionally uses a single belay at the pitch head with thicker 10–11 mm rope that can tolerate rock contact. Faster to rig and suited to shorter American-style pits. Ascending long pitches takes more effort because the full rope hangs as a single load. On large drops this style is being increasingly supplemented with rebelays even in the US.
Rope Diameter and Weight
The choice of rope diameter is a balance between weight, durability, and handling. For Alpine SRT on long or multi-pitch trips, 8–9 mm rope is the practitioner's choice — lighter to carry and fast through bobbin descenders. For shorter American-style pits or abrasive environments, 10–11 mm offers better wear resistance and more comfortable handling through a rack.
Typical weight per metre (kernmantle static rope)
- 8 mm — approx. 42 g/m (e.g. Beal Antipodes, Petzl Ranger)
- 9 mm — approx. 53 g/m (common Alpine SRT diameter)
- 10 mm — approx. 65 g/m (American SRT standard)
- 11 mm — approx. 79 g/m (heavy-duty IRT rope)
Always verify against the specific rope's technical datasheet. The figures above are representative for typical caving-grade static kernmantle; actual weight varies slightly by manufacturer and construction.
Rebelays and Deviations — What They Cost in Rope
Rebelay (~1 m per rebelay)
A rebelay is a full re-anchor partway down the pitch. The rope is knotted (usually a figure-8 on a bight with a loop for the carabiner) and re-attached to a bolt or natural anchor. This consumes roughly 0.5–1 m of rope for the knot itself, plus any slack in the loop. This calculator uses 1 m per rebelay as a conservative allowance.
Deviation (negligible extra rope)
A deviation is a short tape or cord attached to the rock with a carabiner through which the main rope passes. Because the main rope simply runs through the carabiner, no rope is "used up" — only deflected. The calculator counts deviations for reference so you can plan your rigging hardware, but adds no rope length for them.
Common Mistakes When Planning SRT Rope
- Measuring depth at the bottom of a slope, not from the anchor — always measure from the rigging point, not the floor of the entrance passage.
- Forgetting the traverse line — the approach rope from backup belay to pitch lip is consumed rope that won't reach the bottom.
- No bottom tail — a rope that ends exactly at the pitch floor can swing and leave no end for the last ascender move-off. Always add 1–2 m beyond the bottom.
- Using the same rope length for a re-rigged pitch — if you add a rebelay on the return, you need more rope than on the original descent.
- Ignoring water-soaked rope weight — wet rope is significantly heavier; if crossing water passages, factor this into your load estimate.
FAQ
For a basic single-hang pitch you need the pitch depth plus: the anchor setback distance (rope from backup anchor to pitch lip), roughly 2–3 m for Y-hang knots, 1 m per rebelay, and a 1–2 m safety tail at the bottom. A common rule of thumb for a straightforward pitch with a Y-hang and no rebelays is to add 5–7 m to the measured depth. Add 1 m more for each rebelay after that.
Modern Alpine-style SRT uses 8–9 mm low-stretch kernmantle rope to save weight. American-style cavers often prefer 10–11 mm for abrasion resistance when the rope may contact the rock. Always use a static or semi-static caving-grade rope — never dynamic climbing rope, which stretches far too much for ascending.
A rebelay is an intermediate anchor point partway down a pitch where the rope is re-knotted and re-attached to the rock. Cavers must perform a changeover — transferring weight from one rope section to the next. Rebelays keep the rope free of the rock on long drops, avoid waterfalls, and allow the rope to follow a free-hanging line around overhangs.
A rebelay is a full re-anchor: the rope is knotted at a new belay, and the caver transfers between two rope sections. A deviation is a lighter redirect — a tape/cord with a carabiner that pulls the rope sideways, bearing only a fraction of the caver's weight. Deviations are quicker to pass and consume no extra rope length, but offer less course correction than a rebelay.
Typical kernmantle caving rope weights: 8 mm ≈ 42 g/m, 9 mm ≈ 53 g/m, 10 mm ≈ 65 g/m, 11 mm ≈ 79 g/m. Always check your rope's technical datasheet for the precise figure. A 40 m pitch with 9 mm rope means roughly 2.1 kg of rope to carry — multiply across multiple pitches and you quickly understand why Alpine cavers prefer thin rope.
Yes. Many cavers carry rope in bags and re-use the same length on different pitches. This calculator lets you plan each pitch separately, then see the total rope for the trip, helping you decide whether to carry one long rope or split into shorter sections. On deep or multi-drop systems, separate bags per pitch or per section keeps rigging manageable.
⚠ This calculator is an estimate for planning purposes only. Actual rope requirements depend on on-site conditions, anchor placement, and rigging decisions. It is not a substitute for SRT training from a qualified instructor. Always carry a safety margin of rope and never attempt vertical caving without proper training and equipment.