Anchor Chain Length Calculator
Estimate required chain and total rode from depth, tide, bow height, scope, and weather load.
⚓Quick Anchorage Presets
⚙Anchoring Inputs
📊Anchoring Spec Grid
📘Reference Tables
| Condition | Suggested Scope | Wind Band | Common Practice |
|---|---|---|---|
| Lunch stop / crew aboard | 3:1 | < 10 kn | Short stay with active watch |
| Evening settled anchorage | 4:1 to 5:1 | 10 to 15 kn | Normal overnight in protected bay |
| Fresh breeze overnight | 6:1 to 7:1 | 15 to 25 kn | Increase scope before dark |
| Frontal or squall scenario | 8:1 to 10:1 | 25+ kn | Max scope allowed by swing room |
| Chain Size | Approx Weight (lb/ft) | Approx Weight (kg/m) | Typical Boat LOA |
|---|---|---|---|
| 1/4 in (6 mm) | 0.74 | 1.10 | 20 to 30 ft |
| 5/16 in (8 mm) | 1.12 | 1.67 | 28 to 38 ft |
| 3/8 in (10 mm) | 1.50 | 2.23 | 35 to 48 ft |
| 7/16 in (11 mm) | 1.95 | 2.90 | 45 to 58 ft |
| Depth At Bow | 5:1 Rode | 7:1 Rode | 10:1 Rode |
|---|---|---|---|
| 15 ft | 75 ft | 105 ft | 150 ft |
| 25 ft | 125 ft | 175 ft | 250 ft |
| 35 ft | 175 ft | 245 ft | 350 ft |
| 45 ft | 225 ft | 315 ft | 450 ft |
| Anchorage Scenario | Depth + Bow + Tide | Scope Used | Rode Needed |
|---|---|---|---|
| Protected cove overnight | 22 ft | 5:1 | 110 ft |
| Open bay in gusts | 24 ft | 7:1 | 168 ft |
| Strong current inlet | 28 ft | 8:1 | 224 ft |
| Pre-frontal anchorage | 30 ft | 10:1 | 300 ft |
Choosing the right amount of anchor chain depends on the boat and the conditions. For several kinds of boats you usually advise 6 feet of 3/16-thick chain. In deep water over rocky soil with strong wind and rough waves you can use 20 feet of 1/4 chain.
Common rule-of-thumb says that the chain length match the length of the boat. So for a 30-foot ship that gives 15 to 30 feet of chain. Some offer each one foot of chain for every foot of boat length.
How Much Anchor Chain to Use
Weight of the chain matters more than its length. It must have enough mass to hold the shank of the anchor on the sea floor during the anchor sets itself. That weight helps the anchor lie well on the bottom.
It keeps also the pull almost flat. Rope has a bit of lift, what can affect the shank incline down when you leave the anchor backwards. The chain stops the rope rub against the seabed and forms the best angle between ride and soil.
It can also prevent chafing and wear.
The whole anchor rode is made up of nylon rope and chain together. That total length should be 4 to 7-times the expected depth of the anchor. In more crowded anchorages you commonly choose shorter rode, because boats do not have space for broad swing.
For shallow anchor between 5 and 8 meters the catenary length in meters match the wind speed in knots. At 15 meters depth it grows to 1.5-times and reach 2 at 20 meters. Minimumume 6 feet of chain you should use for every 25 feet of water depth.
Other general advice is 3 meters of chain for every meter of depth. So theoretical 21 meters of chain would allow anchor in 7 meters of water. Usually you marks the chain in three meter intervals because of that.
Scope shows the proportion between the length of the anchor rode and the height of the ship above the bottom. Use scope of 5:1 or more is important. For lightweight anchor on small boat in good weather 5:1 already suffice and save money.
For a 24-foot ship usage of longer chain lengths as 6 to 12 feet instead of the usual 4 to 6 allow shorter scope. That helps in very deep water or full places.
