Enter your fence run and post spacing — get post count, post length, hole depth, hole diameter, and concrete bags in seconds. Frost line depth auto-adjusts by state.
Posts are the skeleton of your fence. Get the spacing, depth, or concrete wrong — and the whole structure pays for it.
Use Expert Mode for a fast takeoff or Step-by-step Mode for a guided 6-step workflow.
Every input updates the estimate, SVG preview, and share URL.
The calculator uses your fence material to set the correct post size, hole diameter, and hole depth. 8 ft OC is standard for wood and vinyl, 6 ft OC is recommended for tall or windy fences, and 10 ft OC is standard for chain link.
Line posts are calculated automatically, but end, corner, and gate posts must be counted manually. Your state determines the frost line depth, which sets the minimum hole depth.
Full concrete fill is strongest. The hybrid method saves concrete in well-drained soils. Results show total post count, post dimensions, hole specs, bags per post, and total bags.
The formulas used for planning:
| Fence Run | 6 ft OC | 8 ft OC | 10 ft OC |
|---|---|---|---|
| 50 ft | 9 posts | 7 posts | 6 posts |
| 100 ft | 17 posts | 13 posts | 11 posts |
| 150 ft | 26 posts | 20 posts | 16 posts |
| 200 ft | 34 posts | 26 posts | 21 posts |
| 300 ft | 51 posts | 39 posts | 31 posts |
The starting post rule: a straight run needs a post at both ends. Count end, corner, and gate posts separately so you do not under-order terminal posts.
The 1/3 rule: post depth below grade should be at least one-third of total post length, and always below frost depth.
| Fence Height | Post Length | Min Hole Depth | Notes |
|---|---|---|---|
| 4 ft | 6 ft | 24" | Standard residential |
| 6 ft | 8 ft | 24-30" | Most common backyard fence |
| 8 ft | 10-11 ft | 30-36" | Permit required in most cities |
| 10 ft | 13-14 ft | 36-42" | Commercial / security |
| Region | States | Frost Depth |
|---|---|---|
| Deep South | TX, FL, GA, LA, SC | 0-12" |
| Mid-South | NC, TN, AR, OK | 6-18" |
| Mid-Atlantic | VA, MD, PA, NJ | 12-24" |
| Midwest | OH, IN, IL, IA, MO | 24-36" |
| Upper Midwest | MN, WI, MI, ND, SD | 42-48" |
| Mountain / NE | MT, VT, ME, NH, NY | 36-48"+ |
Always add 6" below the frost line as a safety buffer. In Minnesota, a 6 ft fence may need 10 ft posts rather than standard 8 ft posts.
Concrete is estimated from hole volume minus post displacement, then divided by bag yield.
| Bag Size | Yield | Typical Use |
|---|---|---|
| 40 lb | 0.30 ft³ | Small decorative posts |
| 50 lb | 0.375 ft³ | Light residential |
| 60 lb | 0.45 ft³ | Standard residential |
| 80 lb | 0.60 ft³ | Heavy / gate posts |
| Post Type | Hole Size | Hole Depth | Bags (60 lb) |
|---|---|---|---|
| 4x4 wood standard | 10-12" dia | 24" | 1-1.5 bags |
| 4x4 wood deep / frost | 10-12" dia | 30-36" | 1.5-2.5 bags |
| 6x6 wood gate / corner | 12-16" dia | 30-36" | 2.5-4 bags |
| Chain link line post | 6-8" dia | 24" | 0.5-1 bag |
| Chain link terminal | 8-10" dia | 30" | 1-1.5 bags |
| Gate post any material | 10-12" dia | 36-42" | 3-4 bags |
Gate posts always need more concrete. Undersized gate footings are the leading cause of gate sag.
The 3x rule: hole diameter should be about 2-3x the post width.
| Post Size | Post Width | Recommended Hole Diameter |
|---|---|---|
| 4x4 wood | 3.5" | 10-12" |
| 6x6 wood | 5.5" | 12-16" |
| Vinyl 5x5 | 4.5" | 10-12" |
| Chain link 1-5/8" | 1.625" | 6-8" |
| Chain link 2-3/8" | 2.375" | 8-10" |
| Aluminum 2x2 | 2" | 8-10" |
Wider holes cost more in concrete but improve stability in loose or sandy soil.
| Spacing | Best For | Trade-off |
|---|---|---|
| 6 ft OC | 8 ft+ fences, high-wind areas, heavy panels | More posts, more cost, maximum rigidity |
| 8 ft OC | Standard wood & vinyl privacy fences | Best balance of cost and strength |
| 10 ft OC | Chain link, split rail, open-style fences | Fewer posts, lower cost, less rigidity |
| 12 ft OC | Temporary / utility fencing only | Not recommended for permanent installations |
Wider spacing increases sag risk with heavy materials like board-on-board wood or thick vinyl panels. In high-wind zones, use 6 ft OC regardless of fence height.
Every doubling of spacing roughly quadruples bending force on each post during high winds.
| Fence Height | Standard Post | Gate / Corner Post | Notes |
|---|---|---|---|
| 3-4 ft | 4x4 | 4x4 or 4x6 | Decorative, picket |
| 5-6 ft | 4x4 | 4x6 or 6x6 | Standard privacy |
| 7-8 ft | 4x6 or 6x6 | 6x6 | Permit required most cities |
| 9-10 ft | 6x6 | 6x6 | Commercial / security |
Always use pressure-treated lumber rated for ground contact, such as UC4B or UC4C, for posts set in concrete or soil.
For gates wider than 4 ft, use 4x6 or 6x6 posts. The extra $15-$30 prevents expensive gate sag repairs.
| Type | Set Time | Cure Time | Cost Premium | Best For |
|---|---|---|---|---|
| Standard concrete mix | 1-2 hrs initial | 24-48 hrs | Baseline | DIY projects |
| Fast-setting concrete | 20-40 min | 4 hrs | +10-15% | Professional crews, cold weather |
| Expanding foam anchor | 3-5 min | 15 min | +200-300% | Decorative / temporary only |
Standard mix gives DIYers more time to adjust posts plumb. Fast-set is useful when a professional crew needs to continue work the same day.
Use standard concrete mix for a first fence project. Extra working time is more valuable than speed.
Always add 4-6 inches of gravel at the bottom of the post hole. This prevents water from pooling at the post base, reduces wood rot and metal corrosion, improves freeze-thaw drainage, and costs only about $0.50-$1.00 per post.
Use 3/4" crushed stone or pea gravel. Do not use fine sand because it compacts and retains water.
This single step can extend post life by 5-10 years in wet climates.
Posts set at 18" in a 6 ft fence often lean within 1-2 years. Minimum: 24" or 1/3 of post length.
Northern posts set above frost depth will heave every winter and lean after freeze-thaw cycles.
Skipping gravel traps water at the post base and accelerates rot or corrosion.
Gate posts bear dynamic swing loads and need 3-4 bags of concrete.
Standard construction lumber underground can rot in 2-5 years.
Dry-set posts may work in dense clay but fail quickly in sandy or loose soil.
Once concrete cures, a leaning post is difficult to fix. Check two adjacent faces before set.
At 8 ft OC, a straight 100 ft wood or vinyl run needs about 14 posts. At 10 ft OC for chain link, plan 11 posts. At 6 ft OC for high-wind or tall fences, plan 18 posts. Add end, corner, and gate posts separately when planning a shaped perimeter.
Minimum depth is 1/3 of total post length, always below the frost line. A 6 ft fence usually needs 24-30" in warm states. Minnesota, Wisconsin, and similar northern states may need 48-54".
For a standard 4x4 post in a 6 ft fence, plan 1-2 bags of 60 lb concrete depending on hole diameter and depth. Gate posts need 3-4 bags. Chain link line posts often need 0.5-1 bag.
4x4 pressure-treated lumber is standard for 6 ft residential fences. Use 4x6 or 6x6 for gate posts and corners. For 8 ft fences, upgrade all posts to 4x6 or 6x6.
8 ft OC is standard for wood and vinyl privacy fences. 6 ft OC is used for high-wind areas or tall fences. 10 ft OC is standard for chain link, split rail, and open-style fences.
Total post length equals fence height above grade plus hole depth. A 6 ft fence in Texas typically uses 8 ft posts. A 6 ft fence in Minnesota may require 10 ft posts because the hole must reach below frost depth.
Standard concrete is recommended for DIY projects because it gives more time to adjust post plumb. Fast-setting concrete is better for professional crews, cold-weather installs, or same-day continuation.
Yes for permanent fencing. Exceptions include temporary fencing, agricultural split rail in dense rocky soil, or decorative garden borders under 3 ft. Chain link posts in sandy soil especially require concrete.
DIY materials for a 4x4 post commonly run $22-$38 including concrete. Professional labor plus materials often runs $25-$60 per post, with rocky soil adding $10-$25 per post.
Use UC4B or UC4C ground-contact pressure-treated lumber, add a 4-6" gravel drainage layer, slope concrete away from the post, seal cut ends, and keep mulch away from above-grade post faces.
