Gate Post Calculator
Determine 4x4 or 6x6 gate post sizing, minimum embedment depth, and concrete volume needed to resist gate sag under load.
Gate post sizing & footing
Enter your measurements and the result updates as you type.
Overview
Gate posts endure constant dynamic leverage and slamming impact that regular line posts never face. A gate post that flexes even 1/2 inch at ground level can cause a gate latch to misalign completely.
This calculator determines whether your gate width and weight require 4x4 or 6x6 post timber, hole diameter, and the required concrete footing volume.
Common mistakes
- Using a standard 4x4 post for a gate leaf wider than 4 feet or heavier than 100 pounds.
- Digging gate post footings to standard shallow depth instead of sinking them 36 to 48 inches deep.
- Hanging the gate before concrete footings have cured for at least 72 hours.
- Fastening gate hinges into end-grain or near post edges without pre-drilling pilot holes.
Related calculators
- Double Gate Calculator Calculate exact frame widths for each leaf of a double driveway gate with hinge clearances and center drop rod spacing.
- Fence gate calculator Plan the opening, the posts that carry it and the hardware a fence gate needs, for a walk gate or a double drive gate.
- Fence post calculator Calculate line posts, corner posts and end posts from run length and spacing, with concrete for each post included in the take-off.
- Fence Post Hole Calculator Calculate post hole diameter, depth, cylinder volume, and 60 lb or 80 lb concrete bags needed for sturdy fence footings.
Related reading
In-depth guides
Frequently asked questions
When is a 6x6 post necessary for a fence gate?
Use a 6x6 post for any gate leaf wider than 4 feet, any privacy gate over 5 feet high, or any gate weighing more than 100 pounds.
How deep should gate posts be set in concrete?
Gate posts should be set at least 36 to 48 inches deep (or below the regional frost line), roughly 12 inches deeper than standard line posts.
How much concrete does a 6x6 gate post hole take?
A 14-inch diameter hole 36 inches deep requires roughly 5 to 6 bags of 60 lb concrete mix to anchor the post securely against leverage.
Can you use steel posts instead of 6x6 wood posts for gates?
Yes. Schedule 40 galvanized steel pipe (2-7/8 in or 3 in O.D.) or 4x4 square steel tubing provides exceptional rigidity without warping.
Why do fence gate posts tilt over time?
The continuous cantilevered weight of the open gate exerts constant rotational torque. Shallow footings, soft soil, or wet concrete curing allow the post to lean.
How long should gate post concrete cure before mounting the gate?
Wait at least 48 to 72 hours before hanging the gate. Loading wet concrete pulls the post out of plumb before it reaches full compressive strength.
Should gate posts be linked with an overhead beam?
For wide driveway gates or heavy stockade gates, an overhead pergola header beam locks post tops together and greatly reduces inward sagging over time.
What hardware bolts work best for mounting gate hinges to posts?
Use 3/8-inch or 1/2-inch hot-dipped galvanized carriage bolts or heavy lag screws with washers, pre-drilling pilot holes to avoid splitting the timber.