Why does a 12x16 pergola need a post in the middle?
Because a 16 ft run is longer than a 2-ply 2x8 beam can span between two end posts. With a middle post under each beam, this plan has 6 posts and the beam spans 7'-9-1/4" between them, at 71% used.
Each of the 6 footings here is 30 in pad, 9 in thick, 12 in deep, and the most loaded post is at 15% of its allowable.
The rafters span 11'-6-1/2" between the beams, 78% used, so the long side adds posts and beam length, not heavier rafters.
Planner checks
All 15 planner checks pass for this 12x16 pergola. Local approval not checked.
No check fails and none needs a second look, so nothing here holds up construction. Local approval is still yours to get. Each bar is the percent of its allowable that a member uses, from the span, the loads and the lumber grade. A bar at 100% is at the limit, and over 100% fails.
Rafters, 2x678%of its allowablespan 11'-6-1/2", bending
Slats, 2x26%of its allowablespan 1'-3-1/2", bending
Double beam, 2-2x871%of its allowablespan 7'-9-1/4", bending
Posts, 6x615%of its allowable2,173 lb on the most loaded post
what this plan uses room to spare
Green passes the rule or the calculation we checked against, amber asks you to look at something before you build, red fails it. These are preliminary checks, not a structural approval; your local building authority reviews and approves.
PassRafters 2x6
This plan
11'-6-1/2" span, 1'-2-3/4" overhang
Needed
allowable span 13'-1" with this overhang
Our default
PassSlats 2x2
This plan
1'-3-1/2" span, 0'-3-3/4" overhang
Needed
allowable span 4'-6-3/4" with this overhang
Our default
PassDouble beam 2-2x8
This plan
7'-9-1/4" span, 1'-2-3/4" overhang
Needed
allowable span 9'-3" with this overhang
Our default
PassRafter overhang
This plan
1'-0" past the beam
Needed
no more than a quarter of the 11'-6-1/2" span
Our default
PassBeam overhang
This plan
1'-0" past the end post
Needed
no more than a quarter of the 7'-9-1/4" post spacing
Our default
PassDouble beam to post
This plan
Boards seated in a 1.5 in notch, 2 x 1/2 in bolts for uplift and sideways
Needed
2,093 lb down, 311 lb up, 504 lb along the beam
Our default
PassRafter ties
This plan
Simpson H2.5A at every rafter end: 43 lb uplift and 28 lb along the rafter
Needed
700 lb uplift, 110 lb F2 along the rafter, the sum of the ratios 1.0 or less (catalog C-C-2021, CD 1.6)
6x6: 6 posts, 9'-7-1/4" long, 2,173 lb on the most loaded post. OK, 15% used, governed by column buckling with bending (NDS 3.7 and 3.9)
Knee braces
2x6: 24 in legs at 45 degrees, 3 bolts of 1/2 in at each end, foot at 7'-0", brace let into a 2.00 in housing in the post. OK, 66% used, governed by the bolts or brace compression (907 lb of 1,367 lb)
Beam bolts
2 x 1/2 in: at each post, 1,769 lb. OK, against 2,173 lb down
The footings
Count
6
Size
30 in pad
Depth
12 in
Concrete
41 bags of 80 lb
6 footings
30 in pad, 9 in thick, 12 in deep
Frost depth
12 in, confirm with your building department
Soil bearing
1500 psf assumed
Cost
What it takes to build.
Materials at Home Depot prices, about$2,435.15
Lumber$1,217.80
Hardware$952.08
Concrete$265.27
Home Depot, Hamilton Mill store, prices read 2026-09-30 to 2026-11-04; your store may differ. Quantities and board lengths are exact for this design. Lines marked estimated are priced from a nearby length or another store; special order lines carry no price (special order, price at your lumberyard) and are left out of the total. Before sales tax, delivery, labor and site work.
Home Depot, Hamilton Mill store, prices read 2026-09-30 to 2026-11-04; your store may differ. Quantities and board lengths are exact for this design. Lines marked estimated are priced from a nearby length or another store; special order lines carry no price (special order, price at your lumberyard) and are left out of the total. 15 lines counted off the framing.
Before sales tax, delivery, labor and tools.
Posts and footings
6 posts, 41 bags of 80 lb mix
Rafters
2x6 at 16 in on center
Lines on the list
15
Lumber$1,217.80
6
6x6 x 12 ftShelf price
$314.88
4
2x8 x 20 ftShelf price
$113.52
14
2x6 x 8 ftShelf price
$135.52
15
2x6 x 16 ftShelf price
$292.20
66
2x2 x 8 ftShelf price
$361.68
Hardware$952.08
6
Adjustable standoff post base, 6x6Shelf price
$356.52
36
1/2 x 8 in hex bolt, galvanizedShelf price
$165.96
60
1/2 x 6 in hex bolt, galvanizedShelf price
$214.80
192
1/2 in flat washer, galvanizedShelf price
$86.21
96
1/2 in hex nut, galvanizedShelf price
$49.88
24
Rafter tie (hurricane tie)Shelf price
$23.52
6
Rafter tie over each post, Simpson H11Z or equalSpecial order, no price
not priced
330
Exterior wood screw, 3 inShelf price
$35.21
1
12 in round concrete form tube, 4 ftShelf price
$19.98
Concrete$265.27
41
Concrete mix, 80 lb bagShelf price
$265.27
Home Depot, Hamilton Mill store, prices read 2026-09-30 to 2026-11-04; your store may differ. Quantities and board lengths are exact for this design. Lines marked estimated are priced from a nearby length or another store; special order lines carry no price (special order, price at your lumberyard) and are left out of the total. Change the size in the pergola designer and the list follows.
Free and paid, side by side
Design it free. Build it from the $29 plan.
Free
On this page and in the designer, no account
This design in 3D, and every change you make to it
Every planner check, with its rule and source
Cost estimate
At least $2,435.15 at Home Depot prices in materials, line by line, on this page. See the estimate
Summary PDF
The design, its checks and its materials list on a few pages. A summary, not the build drawings.
You check out in the designer, with this design loaded. If the plan has an error, we fix it or refund you within 30 days. Guarantee terms.
Real sheets from the 12-sheet sample plan for the 12x12 ft pergola
The sample was printed on an earlier date, so its prices can differ from the estimate above. Your plan prints the same prices as the estimate.
Cover and project data
Plan view
Front elevation
Footing, brace and post base details
Member schedule and checks
Shopping list
Build phases
From the first footing to the last slat in 6 phases.
Each picture is this pergola at the end of its phase, drawn by the designer, with that phase's new parts in color.
01
Footings
Stake the post centers, check the diagonals, dig and pour the footings, and set the post bases.
02
Posts
Set the 6x6 posts plumb on their bases and brace them.
03
Beams
Fasten the 2-ply 2x8 beams to the posts with the through-bolts the plan gives.
04
Rafters
Set the 2x6 rafters at 16 in on center across the beams, each tied down.
05
Slats
Fasten the 2x2 slats across the rafters at 8 in on center.
06
Knee braces
Bolt the knee braces between each post and beam in both directions.
This is the summary. The $29 builder's plan breaks these phases into a build order with the new parts highlighted, a how-to detail and a check at each step.
This plan uses 6 posts, with the 2-ply 2x8 beam spanning 7'-9-1/4" between them at 71% of its capacity. The designer picks the post count for you and lets you set it yourself, and the percent used shows at once whether the beam still holds.