⚓ Anchor Scope Calculator
Enter the water depth, your bow-roller height, and the tidal rise, pick a scope ratio, and get the length of rode to pay out — in both feet and metres.
🌊 Depth to Rode Length
What is an Anchor Scope Calculator?
It tells you how much anchor rode to let out for a confident night's hold. Scope is the ratio of rode to depth, but the depth that matters runs from your bow roller — not the waterline — down to the seabed, and it grows as the tide comes in. The calculator adds the water depth, the bow-roller height, and the expected tidal rise into an effective depth, then multiplies by your chosen scope ratio.
Use it before you drop the hook to pick the right amount of chain or rope, and to check you won't be short-scoped at high water. More scope flattens the pull and helps the anchor set, but widens your swinging circle — balance holding against the room around you, and veer more when weather threatens.
❓ Frequently Asked Questions
What scope ratio should I use?
A common rule of thumb is about 5:1 for an all-chain rode, 7:1 for a mixed rope-and-chain rode, and up to 10:1 in strong wind or a swell. Scope is the ratio of rode length to the effective depth from the bow roller. More scope gives a flatter pull that helps the anchor dig in and hold — when in doubt, and if swing room allows, let out more.
Why add the bow-roller height and the tide?
The scope ratio applies to the distance from your bow roller down to the seabed, not just the charted depth. So you add the height of the bow roller above the water and the tidal rise you expect before you weigh anchor. Forgetting the tide is a classic way to end up dangerously short-scoped at high water.
Does more scope always mean a better hold?
Up to a point — more scope flattens the angle of pull and improves holding, but it also increases your swinging circle, so you have to balance security against the room available and other boats around you. In a crowded anchorage you may compromise on scope; in open water with a blow coming, veer more.
Is chain better than rope for anchoring?
All-chain rode is heavy and its catenary (the sag in the middle) keeps the pull horizontal, so it holds well at lower scope and resists chafe on the bottom. Rope is lighter and stretches to absorb shock loads but needs a length of chain at the anchor and more scope overall. Many cruisers use a rope-and-chain combination for the best of both.