Lay Out Your Deck Footprint with Stakes and String
This is where your deck transforms from a plan on paper to a real shape on the ground. Using stakes and string, you'll mark the exact perimeter of your deck and ensure every corner is perfectly square. Get this wrong, and nothing else will fit properly.
Quick Summary
Time needed
1-2 hours
Cost
$20-50
Difficulty
Moderate precision
Why Layout Accuracy Matters
Your deck is essentially a large rectangle that must be perfectly square. If your corners are off by even an inch, you'll see it when installing decking boards—they'll taper toward one side, and the last board won't fit right. Worse, your posts won't align with your beams.
Critical concept: The string lines you set now become the reference for everything else: post hole locations, beam placement, and joist positions. Take your time and get it right.
The good news is that checking for square is simple with the 3-4-5 triangle method. Once you understand it, you can verify any corner in minutes.
What You'll Need
Materials
- •Wooden stakes — 8-12 pieces, 1x2 or 2x2
- •Mason's line — 100+ feet of strong string
- •Marking paint — For temporary ground marks
- •Batter boards (optional) — For precision layouts
Tools
- •Tape measure — 25 feet minimum, 50 feet better
- •Hammer or mallet — For driving stakes
- •Line level — Clips onto string to check level
- •Speed square — Quick 90-degree reference
Step-by-Step Layout Process
1. Establish the Ledger Line
If your deck attaches to the house with a ledger board, start there. The ledger defines one entire side of your deck.
- •Mark the left and right ends of where the ledger will go
- •Use a level or laser to ensure both marks are at the same height
- •Account for ledger height—typically 1-3 inches below door threshold
Freestanding deck? If your deck won't attach to the house, start by establishing one side using stakes and string. This becomes your reference edge.
2. Set the First Corner Stakes
From the ends of your ledger line, run perpendicular lines outward to establish the side edges of your deck.
Quick Square Check
Use a speed square against the house wall to get your string roughly perpendicular. Then verify with the 3-4-5 method (next step).
- •Drive stakes about 2 feet beyond where corners will actually be
- •This extra distance lets you adjust string positions
- •Tie string tightly—loose string causes inaccurate measurements
3. Square Corners with the 3-4-5 Method
This ancient technique uses the Pythagorean theorem to verify right angles. It's foolproof and requires only a tape measure.
The 3-4-5 Triangle Method
Step A: Measure 3 feet from the corner along one string and mark it
Step B: Measure 4 feet from the corner along the other string and mark it
Step C: Measure the diagonal between those two marks
If the diagonal is exactly 5 feet, your corner is square!
Pro tip: For larger decks, use bigger multiples: 6-8-10, 9-12-15, or 12-16-20. Larger triangles give more accurate results because small measurement errors matter less.
4. Complete the Rectangle
With two corners squared to the house, set the remaining corner stakes and run string along the far edge of the deck.
- •Measure carefully—the far edge should be the same length as the ledger
- •Verify both side strings are the same length
- •Square the far corners using the 3-4-5 method
5. Verify with Diagonal Measurements
The final check: measure both diagonals of your rectangle. In a perfect rectangle, both diagonals are exactly equal.
Diagonal A = Diagonal B
If they're not equal, adjust corners until they match
Troubleshooting: If diagonals don't match, the longer diagonal tells you which corner is pushed out. Move that corner inward and re-measure.
6. Mark the Ground
Once everything is square, transfer the string lines to the ground with marking paint. This preserves your layout if strings get disturbed.
- •Spray paint directly under each string line
- •Mark corner intersections clearly
- •Leave stakes and string in place for the next step
Common Mistakes to Avoid
Using loose string
String that sags or can move in the wind gives false measurements. Pull string tight and secure it firmly to stakes. In windy conditions, spray string with water to reduce movement.
Assuming the house is straight
Many houses have walls that bow or shift over time. Measure from multiple points along the wall and adjust your layout accordingly. Decide if you want the deck parallel to the wall or truly square.
Not double-checking with diagonals
The 3-4-5 method checks individual corners, but the diagonal check verifies the entire rectangle. Always do both. A rectangle can have all 90-degree corners and still be a parallelogram if opposite sides aren't equal.
Measuring from different starting points
Be consistent with where you measure from. If measuring to the outside of the deck, always measure to the outside. Mixing inside and outside measurements causes errors.
Frequently Asked Questions
What is the 3-4-5 triangle method?
It uses the Pythagorean theorem to verify right angles. Measure 3 feet along one side, 4 feet along the adjacent side. If the diagonal between those points is exactly 5 feet, you have a 90-degree corner. Use larger multiples (6-8-10, 9-12-15) for greater accuracy.
How far should posts be from the house?
This depends on your joist span and lumber size. For 2x8 joists, the beam is typically 8-10 feet from the house. For 2x10 joists, 10-12 feet. The beam location determines where outer posts go. Check span tables for your specific setup.
Why don't my diagonal measurements match?
Unequal diagonals mean the layout isn't square. The longer diagonal indicates which corner is pushed out. Adjust the corner stakes until both diagonals are exactly equal. Even half an inch difference causes problems with decking.
What if my house wall isn't straight?
You have two choices: follow the wall (deck inherits the curve) or snap a straight reference line (visible gap between deck and house). Most builders follow the wall to avoid obvious gaps. Measure from multiple points and adjust.
Ready for the Next Step?
With your footprint laid out and square, it's time to mark the exact locations where your post holes will go.