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The total length of the W-beam guardrail run.
Measure the full end-to-end length of the guardrail run along the roadway.
The center-to-center spacing between guardrail posts.
6.25 ft (1.905 m) is the AASHTO Roadside Design Guide standard post spacing for W-beam guardrail; tighter spacing (e.g. half spacing) may be specified in transition zones or at bridge approaches.
Guardrail posts needed
54 posts
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Highway Guardrail Post Spacing Calculator: 54 posts — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- Post count = ceil(guardrail length ÷ post spacing) + 1, the standard layout method for W-beam guardrail posts, commonly spaced at 6.25 ft (1.905 m) per AASHTO Roadside Design Guide standard post spacing
Inputs used
- Guardrail Run Length
- 330 ft
- Post spacing
- 75 in
What this calculation does not cover
- The run length is an input here, not an output, and it is the number that decides whether the barrier works at all. Length of need comes from the hazard's offset from the traveled way, the design speed and traffic volume, and the runout length tables in the Roadside Design Guide. A barrier that stops short lets a vehicle round its end and reach the hazard it was installed to shield.
- Every post counted is a line post. A crashworthy end terminal is a proprietary assembly with its own posts, its own post types — breakaway timber in soil tubes, or steel posts in foundation sleeves — and its own spacing across the first 37.5 to 50 ft (15 m) of the run. On a run terminated at both ends, a sizable share of this count is neither the post nor the spacing being priced.
- Post count says nothing about post length or embedment, and embedment is what lets a post yield rather than tear out of the ground. Depth is set by the soil and by the conditions a standard drawing does not assume: a post behind a curb, on a fill slope, or through a concrete mow strip is a different detail, often a longer post or a leave-out. Correct spacing over insufficient embedment gives the rail nothing to work against.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
Part of a bigger job
Or plan the space itself: measure it once, doors and windows included, and this figure comes back worked out on that space, with what goes with it.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-06 · in the site-wide review of 2026-09-06 · v1.0.1
Regulatory standards & verification citations1
- Post count = ceil(guardrail length ÷ post spacing) + 1, the standard layout method for W-beam guardrail posts, commonly spaced at 6.25 ft (1.905 m) per AASHTO Roadside Design Guide standard post spacing
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