Floating Deck Calculator
Plan a floating (ground-level) deck — enter the size to get the number of deck blocks, joists, deck boards and the gravel base you need, with an estimated material cost.
How to plan a floating deck
A floating deck sits on precast deck blocks on a gravel base instead of dug footings, and it isn't attached to the house — which is what makes it a fast, beginner-friendly build. The number of blocks comes from a grid (typically one every 4 feet in each direction), and the framing and decking follow from the deck size. The calculator above works out blocks, joists, deck boards and the gravel base, plus a rough material cost.
blocks = (length ÷ spacing + 1) × (width ÷ spacing + 1)
Deck blocks by size (4 ft grid)
| Deck size | Block grid | Deck blocks |
|---|---|---|
| 8 × 8 ft | 3 × 3 | 9 |
| 10 × 10 ft | 3 × 3 | 9 |
| 12 × 12 ft | 4 × 4 | 16 |
| 12 × 16 ft | 4 × 5 | 20 |
Floating decks are usually kept low and small, and rules vary, so check whether your size and height need a permit before you start. Choosing materials? Compare boards and budget with the deck cost calculator and the deck board calculator.
Frequently asked questions
What is a floating deck?
A floating deck is a low, ground-level deck that rests on precast deck blocks instead of footings dug below the frost line, and it is not attached to the house. That makes it simpler and faster to build, which is why it is a popular DIY project for patios and backyard seating areas.
How many deck blocks do I need for a floating deck?
Deck blocks support the beams and joists, typically spaced about every 4 feet in both directions. For a 12×12 floating deck that is roughly 16 blocks. The calculator works out the block grid from your deck size, and you can add more for heavier loads or longer spans.
What goes under a floating deck?
Most floating decks sit on a compacted gravel base under each block, which keeps the blocks from settling and improves drainage. The calculator estimates the gravel volume for a base pad. Landscape fabric under the gravel helps suppress weeds.
Do I need a permit for a floating deck?
Rules vary by location. Many areas exempt small, low, unattached decks below a certain size and height, but others require a permit regardless. Check with your local building department before you start — this calculator sizes the materials but does not cover code or permits.