Boat Lift Capacity Calculator
Quick answer
Your lift must carry the boat as it actually sits on the cradle, not its brochure dry weight. Add fuel (about 6.1 lb per gallon of gasoline), water, any ballast left aboard, batteries and gear, then choose a lift rated at least 15 to 25% above that loaded weight.
On this page
Lift capacity calculator
Results appear here as you type.
Assumes a load centered on the cradle. Many lifts are rated with the load centered fore and aft; a heavy stern or off-center engine reduces the effective capacity. Confirm with the lift manufacturer's rating and loading instructions.
How the calculator works
The calculator builds a loaded weight from the parts that change between the spec sheet and your slip, then adds a margin. Each line uses a fixed, published conversion so you can check it by hand:
| Item | Weight used | Why it matters |
|---|---|---|
| Gasoline | 6.1 lb per US gallon | A full 100 gal tank adds about 610 lb. |
| Diesel | 7.1 lb per US gallon | Heavier than gasoline by about 16% per gallon. |
| Fresh water and ballast water | 8.3 lb per US gallon | 1,000 lb of factory ballast is only about 120 gallons. |
| Batteries | 65 lb each | Group 24 to 31 lead-acid batteries weigh roughly 50 to 75 lb; lithium packs weigh less. |
| Gear | Your estimate | Anchors, chain, coolers, tow ropes, boards, safety gear and fishing gear typically total 300 to 800 lb. |
The suggested rating is then rounded up to the next common capacity class (for example 4,500, 6,000, 7,000, 10,000 or 13,000 lb). Manufacturers use slightly different class steps, so treat the class as a starting point when you read spec sheets. For the reasoning behind each step, read the full capacity sizing guide.
Which dry weight to enter
Builders publish dry weight in different ways, and the difference can be several hundred pounds. Before you type a number, check three things on the spec sheet or in the owner's manual:
- Is the engine included? Many outboard boats list hull weight without the motor. A 150 hp four-stroke outboard is roughly 400 to 500 lb, and a pair of 300 hp outboards can add well over 1,000 lb. Untick the box in the calculator and enter the engine weight if it is not included.
- Which engine? A spec sheet often lists the lightest engine option. If you bought the bigger engine, add the difference.
- Which options? Towers, hard tops, generators, extra batteries, upgraded audio, trim tabs and fixed ballast are rarely in the base figure.
If you cannot find a reliable figure, use the ranges in our boat weight database and choose the 25% margin. The most reliable number of all is a weigh ticket: some marinas and trailer dealers can weigh a boat on its trailer, and you subtract the trailer's weight.
Worked example: 23 ft wake boat
Worked example: wake boat with ballast left aboard
A 23 ft wake boat lists 5,000 lb dry with engine. It carries 60 gal of gasoline, two batteries, about 500 lb of boards, ropes and coolers, and the owner admits the rear ballast tanks (about 100 gal) are not always drained before lifting.
- Dry weight: 5,000 lb
- Fuel: 60 x 6.1 = 366 lb
- Ballast left aboard: 100 x 8.3 = 830 lb
- Batteries: 2 x 65 = 130 lb
- Gear: 500 lb
- Loaded weight: 6,826 lb
- With a 20% margin: 6,826 x 1.2 = 8,191 lb, so a 9,000 or 10,000 lb class lift.
Sized from the 5,000 lb brochure figure with a 20% margin, the same owner might have bought a 6,000 lb lift and been over its rating every time the ballast stayed in.
Why a margin, and how much
A margin is not padding for its own sake. It covers three real things: weight you have not counted (water in the bilge, wet gear, an extra cooler), uneven loading (most of the weight of an outboard boat sits near the stern, so one end of the lift carries more than half the load), and wear (cables, sheaves and gearboxes last longer when they are not run at their limit every cycle).
- 15% is a floor for well documented weights, fresh water and light use.
- 20% is the sensible default for most owners.
- 25% or more makes sense in salt water (where corrosion slowly reduces strength), for heavy daily use, for boats whose weight you are estimating, and for boats that will get heavier (a planned tower, a bigger engine, more ballast).
Safety: a lift rating is not a reason to stand under a boat. Never stand, swim or work beneath a raised boat, whatever the margin.
What the calculator does not know
It cannot see how your weight is distributed or how your lift's manufacturer defines its rating. Some ratings assume the load is centered between the lifting points; a boat with twin outboards hanging off the transom can put substantially more than half its weight on the rear cables or cylinders. If your boat is stern-heavy, ask the manufacturer how its rating applies and consider the next class up. Pontoons and tritoons also need bunks or brackets matched to the tube spacing; see pontoon boat lifts.
Frequently asked questions
How much bigger than my boat should a boat lift be?
Size the lift at least 15 to 25% above the boat's loaded weight, not its dry weight. Loaded weight includes fuel, water, batteries, gear and any ballast that may be left in the tanks. For most owners a 20% margin over a realistic loaded weight is the right starting point, with 25% for salt water or uncertain weights.
Does boat lift capacity include the weight of the engine?
Lift capacity is the total load the lift can raise, so the engine always counts. The question is whether your boat's published dry weight already includes it. Many outboard boats list hull weight only, so check the spec sheet and add the engine weight if it is missing.
How much does a full tank of gas add to my boat's weight?
Gasoline weighs about 6.1 lb per US gallon, so a 50 gal tank adds about 305 lb and a 100 gal tank about 610 lb. Diesel is heavier at about 7.1 lb per gallon. Size the lift for full tanks, because boats are often lifted right after fueling.
Can I put a boat on a lift that is slightly over capacity?
You should not. Running over the rating accelerates cable, sheave and gearbox wear and removes the margin that protects you from a failure. If your loaded weight is close to or above the rating, reduce the load before lifting (drain ballast, remove gear) and plan to upgrade the lift.
What if I can't find my boat's dry weight?
Look on the builder's website, the owner's manual, or archived brochures for your model year. If none exist, have the boat weighed on its trailer and subtract the trailer weight, or use typical ranges from our boat weight database with a 25% margin.
Sources and further reading
- Fuel and water densities: standard engineering values for gasoline (about 6.1 lb/gal), diesel (about 7.1 lb/gal) and fresh water (about 8.3 lb/gal) at typical temperatures.
- U.S. Coast Guard, boat capacity information and capacity plates: uscgboating.org.
- Manufacturer owner's manuals for boat lifts, which define each product's rated capacity and loading instructions.
- Boat Lift Lab, data methodology.