Anchor Scope Calculator

Scope is the ratio of rode paid out to the total height from the seabed up to your bow roller. A higher ratio lays the rode at a flatter angle, so the pull on the anchor is more horizontal and the flukes dig in and hold rather than break out.

A common guide is 5:1 for all-chain rode in settled conditions, 7:1 for rope or a rope and chain mix, and 10:1 when wind or swell builds. The tool gives one-tap 5:1, 7:1 and 10:1 presets, but you can type any ratio of at least 1.

Scope is measured from the seabed to the bow roller, not from the sea surface, because that is where the rode leaves the boat. Adding the bow height and the tide rise you still expect keeps the ratio honest once the water is at its highest.

Read the depth when you drop the anchor, then put the extra rise you expect into the tide field. The calculator sums both, so the rode is long enough to keep your scope once the tide floods in.

In practice, yes. Heavy all-chain rode sags into a catenary curve that absorbs surge and pulls more horizontally, so it holds at a lower scope. Lighter rope stays straighter and needs more scope for the same holding, which is why the rope guideline is higher.

Yes. Toggle to m and every field, including the results, is shown in meters. Switching units also converts the numbers already in the boxes, so you do not have to retype them.

No. It is the length of rode to pay out, not the radius of your swinging circle. Your swing is roughly the rode length plus your boat length from the anchor, so leave clearance from other boats, moorings and hazards.

In a crowded anchorage you may have to reduce scope, which lowers holding, so compensate with an anchor watch, an alarm or extra chain if the wind gets up. The tool shows the ideal rode for your ratio, and it is up to you to fit it to the space and the forecast.

No. Every calculation happens locally in your browser using simple arithmetic, so your depths and settings never leave your device and the tool keeps working without a signal once loaded.