How to use the guardrail quantity calculator
Enter the length of the run, the rail height, the number of mid rails and the post spacing and the page returns the total horizontal member length, the total post length and the number of posts. Enter the opening width and length with a margin on each side and the opening area and the area the cover has to span appear as well.
The work is geometric. The post count is the run length divided by the spacing, rounded up, plus one post for the far end. The horizontal length is the run multiplied by one top rail plus the number of mid rails. The cover area is the rectangle formed by adding the margin twice to each opening dimension. Rounding up is applied once, at the post count, and the result label says so. Enter the run and post spacing in feet and the rail height, opening sizes and margin in inches; lengths come back in feet and areas in square feet, each with the metric value in parentheses. Values are as of October 2026.
Statutory figures such as rail heights, allowable rail loads and cover load criteria were not confirmed in an authoritative source, so none are given and you enter the values read from the standard you apply. Load checks, member section checks and anchorage of the fixings are not covered. This calculator is for reference and does not replace design. Review by a qualified engineer is required.
Frequently asked questions
Statutory heights and allowable loads were not confirmed in an authoritative source, so none are given. Read the height from the standard you apply, enter it, and the quantities follow that height.
The run length is divided by the spacing, rounded up, and one is added for the far end post. Rounding up means an uneven spacing never leaves the run short.
Load checks for the rail and the cover are not covered. This page works out member lengths, post count and the opening and cover areas only.