Size and depth
The single biggest driver is size. A larger pond needs more digging, more liner, more stone and a bigger pump and filter. Depth matters too, since deeper ponds need more excavation and stronger planning.
Ask how the estimate was built. A fair estimate states the pond dimensions, the depth and the equipment included.
Stone and finishing
Stone is a major line item. Large boulders and natural ledge stone cost more than gravel and small rock, and delivery plus placement adds to it. A rocky, natural look takes more stone than a clean, minimal one.
Ask whether stone is included, how much and what kind.
Equipment and filtration
Pumps, skimmers, filters, UV clarifiers, aeration and lighting all add up. A modest garden pond needs less than a koi pond with a bottom drain and a drum filter. The right equipment saves money in the long run through less cleaning and fewer problems.
Access and site conditions
A yard that equipment can reach is cheaper to dig than one that needs hand work. Slopes, rock, tight gates and tree roots all add time. A site visit lets a contractor see these before quoting.
Power, water and extras
New electrical circuits, an auto-fill line, a bridge or a deck add their own costs. They are easy to forget when comparing quotes. Ask what is included and what you would need to arrange separately.
How to compare quotes
Compare scope, not only totals: dimensions, depth, liner type, stone, equipment, plants, startup and cleanup. Ask for a written estimate and how the price changes if conditions differ.
Compare written scopes, ask what equipment and stone are included and visit past projects if you can.
