T-Post Calculator
A T-post calculator counts posts as perimeter ÷ spacing, rounded up: a 100 × 100 ft field with posts 8 ft apart needs 50 T-posts, or $400 at $8 each.
T-post calculator: counting posts
A T-post calculator finds how many steel T-posts you need to fence a field by dividing the distance around it by the spacing between posts. Because the fence closes on itself, each section ends at a post and the last section meets the first, so the number of posts equals the number of sections. The result is rounded up, since you cannot buy a part of a post.
Perimeter = 2 × (length + width). Posts = perimeter ÷ spacing, rounded up. Cost = posts × price per post.
The spacing goes in the depth box. If you leave it empty, the tool uses 8 ft.
What a T-post is
A T-post is a steel post with a T-shaped cross-section. It has studs or tabs along one side to hold wire, and a flat anchor plate near the bottom that keeps it from pulling out. You drive it with a hand-held post driver. It is light, strong, and cheaper than wood, which is why it is common for pasture, garden, and property-line fences.
Worked examples
Example 1, the default field. 100 ft × 100 ft, posts every 8 ft, $8 each.
- Perimeter: 2 × (100 + 100) = 400 ft
- Posts: 400 ÷ 8 = 50
- Cost: 50 × $8 = $400
Example 2, a rectangular paddock. 150 ft × 80 ft, posts every 10 ft.
- Perimeter: 460 ft
- Posts: 460 ÷ 10 = 46
- Cost: 46 × $8 = $368
Example 3, a spacing that does not divide evenly. 200 ft × 120 ft, posts every 12 ft.
- Perimeter: 640 ft
- Posts: 640 ÷ 12 = 53.33, rounded up to 54
- Cost: 54 × $8 = $432
Posts by spacing for a 400 ft perimeter
| Spacing | Posts |
|---|---|
| 6 ft | 67 |
| 8 ft | 50 |
| 10 ft | 40 |
| 12 ft | 34 |
| 16 ft | 25 |
Doubling the spacing roughly halves the post count, but a wider gap lets the wire sag and animals lean on it.
What the count does not include
- Corner, end, and gate posts. These are larger and braced, so count them separately.
- Wire, fabric, or fence panels
- Clips or ties to hold the wire to each post
- Braces and tension hardware
- A post driver, if you do not own one
A rule of thumb is to subtract the corner and gate posts from the T-post count, since those spots use a different post. For a four-corner field with one gate, that is about six posts.
Measuring the fence line
Walk the line with a measuring wheel or a long tape. Mark the corners with stakes and run a string between them so the line stays straight. Measure along the string. If the ground slopes, measure along the ground surface, since wire follows the slope. Mark each post location with a flag before you start driving.
Driving the posts
- Check for buried lines before you drive. Call the utility locating service in your area.
- Set the post upright with the studs facing the same way down the line.
- Slide the driver over the post and drive it down in steady strokes.
- Stop when the anchor plate is buried. Rocky ground may need a pilot hole.
- Check that the post is plumb as you go.
Wear gloves and eye and ear protection, since the driver is loud and the posts have sharp edges.
Common mistakes
- Using the open-line count for a closed loop, or the reverse.
- Forgetting the corner and gate posts.
- Setting the posts too far apart for livestock.
- Driving posts without checking for underground lines.
- Buying posts that are too short to hold the wire at the right height after burial.
Wire and the post count
Once you have the posts, size the wire to match. Roll wire is sold in set lengths, such as 100 ft or 330 ft, so divide the perimeter by the roll length and round up. For the 400 ft field in example 1, that is four 100 ft rolls with no overlap, but real fences need extra at the corners and gates, so plan for a fifth roll or a partial one. Buy a few extra clips, since they are small, cheap, and easy to drop in tall grass.
Related calculators
The chain-link fence calculator covers a different fence type, the fence post calculator gives another post count, and the fence post depth calculator helps with the hole for the heavier posts.
Frequently asked questions
What spacing is typical for T-posts in a wire or field fence?
Spacing of roughly 8 to 12 ft is common, with closer spacing for livestock pressure or uneven ground and wider spacing for light-duty fences. Check the wire maker's guidance. The calculator defaults to 8 ft.
Do T-posts need to be set in concrete?
Usually not. T-posts are driven into the ground with a post driver, and their anchor plate and studs hold them in firm soil. Corners, ends, and gates need heavier posts, and those are often set in concrete.
Do I still need wood or pipe corner posts if I am using T-posts?
Yes, in most cases. A T-post alone does not hold wire under tension at a corner or end. Builders brace corners with larger wood or steel posts, and the wire is stretched against them.
What length T-post should I buy?
Pick a length that gives the fence height you need plus the depth in the ground. Common lengths run from roughly 5 to 8 ft. Many installers drive the post about 18 to 24 inches deep in firm soil, and deeper where the ground is loose.
Can this calculator handle a single straight fence line instead of an enclosed perimeter?
Not directly. It treats the fence as a closed rectangle. For an open line, divide the length by the spacing, round up, and add one. A 300 ft line at 10 ft spacing takes 30 + 1 = 31 posts.
Estimates only. Verify quantities with your supplier before purchasing.