A fence order goes wrong in two places, and they are not the same place. The panel count comes from the run divided by the panel width. The post count comes from the run divided by the post spacing, plus one for the far end. Those two divisions can use the same number and still produce different answers, which is why a 24 m boundary in 1.8 m panels needs 14 panels but 15 posts. Everything below works from that run, using measurements you take on the ground rather than figures scaled off a plot plan.
Walking the line with a tape, stakes and a string
- Stake both ends before you measure anything. Drive a stake at each end of the boundary, pull a string line between them, and check that the string clears every obstruction. Measure stake center to stake center along the string and write the figure down in meters to two decimal places. Tool: Timber stakes and mason line.
- Break the boundary into straight legs. Every change of direction ends a leg. Record each leg as its own run length, note the angle at each corner, and calculate the legs one at a time. Adding the legs together first will overstate the panel count and understate the number of shared corner posts. Tool: 30 m open reel tape.
- Take the panel width off the product label. Do not measure a panel you already own and assume the new stock matches. Read the stated width on the label, then check whether that figure is the panel alone or the panel plus the channel it slots into, because the difference is the thickness of a post. Tool: Product label or spec sheet.
- Set post spacing from the fixing method. For slotted concrete or steel posts, the spacing is the panel width plus one post thickness measured center to center. For panels face fixed to timber posts, spacing equals the panel width. Enter the spacing you can actually hold on the ground, not the catalog figure. Tool: Folding rule.
- Measure and subtract every gate opening. A 0.9 m pedestrian gate and a 3 m drive gate are hardware dimensions, not panel dimensions. Measure the finished opening, subtract it from the leg it sits in, and count the gate posts separately, since they carry a swinging load the line posts never see. Tool: Tape measure.
- Record the soil and the fall over the run. Note whether the line is sand, general soil or shallow rock, because that decides the hole depth rather than the panel choice. Then measure the drop from one end of the run to the other with a level and a long straightedge, and record it in meters. Tool: Spirit level and straightedge.
The post count follows the gaps, not the panels
Posts sit at the ends of gaps, so a straight run always carries one more post than it carries bays. The tool writes that as posts equal the run divided by the post spacing, rounded up, plus one. For the 24 m example the division gives 13.33, the rounding gives 14 bays, and the added end post gives 15. Panels use a different route: the same 13.33 is multiplied by the waste allowance before it is rounded up. Posts never get that allowance, because a post is not cut down to fit a short bay. A damaged post is replaced one for one, while a panel can be trimmed at the last bay and still do its job. If you order 14 posts for 14 panels, the far end of the run has nothing to fix the final panel to, and the whole line has to be reset from the last good post.
A 24 m garden boundary in 1.8 m panels
| Field | Value |
|---|---|
| length | 24 |
| panelWidth | 1.8 |
| postSpacing | 1.8 |
| waste | 5 |
Enter a run of 24 m, a panel width of 1.8 m, a post spacing of 1.8 m and a waste allowance of 5 percent. The panel route divides 24 by 1.8 to get 13.33 bays, multiplies by 1.05 to get exactly 14.0, and rounds up to 14 panels. The post route divides 24 by 1.8, rounds 13.33 up to 14 bays, and adds the far end post for 15 posts. Two things in that arithmetic are worth noticing. First, the waste allowance changed nothing here, because 13.33 already rounds up to 14 on its own. Second, the result sits on a knife edge: a run of 24.1 m gives 14.06 panels after the allowance and jumps the order to 15. Buy the 15 posts as 13 line posts and 2 heavier end posts.
Result: 14 panels; 15 posts.
What the straight run assumption leaves out
The formula describes one straight, level leg. Real boundaries rarely are. A corner is a post shared by two legs, so measure and calculate each leg separately and then subtract the shared posts once at the end. The USDA fence specification treats a change in alignment of 20 degrees or more as a braced corner, and notes that across an 8 ft section, 20 degrees is roughly 3 ft off the straight line. Gates are the second omission. A gate leaf replaces a panel but the opening is set by the hardware, not the panel width, so measure it and enter the remaining run. The same specification lets a gate under 100 lb hang from a single properly set end post, and sends anything heavier or wider than 6 ft to the braced pull post of an H assembly. Slopes are the third. A 24 m horizontal run on a 10 percent grade measures about 24.12 m along the ground, which pushes the panel count from 14 to 15.
Post depth, hole size and the numbers that decide them
The tool counts posts. It does not size the holes those posts go into, and the depth is where a cheap fence fails. The USDA specification sets a minimum setting depth of 24 in for a 3.5 in wood line post in general soil, 18 in where rock is shallow, and 30 in in sand, which is the opposite of what most people guess. A hand dug hole should be at least 6 in wider than the post, and backfill has to be tamped in layers no thicker than 4 in. If you use concrete, it is rodded in layers no thicker than 12 in, filled to the ground surface, and left under no load for 24 hours. Two comparisons in that document are worth memorizing: a post driven into an augered pilot hole holds about 5 times better than a hand set post, and a corner post set 2.5 ft deep is about half as strong as the same post set 3.5 ft deep. So the 15 posts in the example are not one product. Thirteen are line posts and two are end posts that need more diameter and more depth.
| Fence component | Minimum size | Setting depth or length | Where it applies |
|---|---|---|---|
| Wood line post, durable heartwood | Top diameter 3.5 in | Depth 24 in in general soil | Straight runs between braces |
| Wood line post in rocky soil | Top diameter 3.5 in | Depth 18 in | Shallow rock under the line |
| Wood line post in sandy soil | Top diameter 3.5 in | Depth 30 in | Loose sand that gives up grip |
| Pressure treated wood line post | Top diameter 3.5 in | Depth 24 in in general soil | Same depths as heartwood posts |
| Steel T post | Weight 1.25 lb per ft | Depth 15 to 18 in | Anchor plate fully below grade |
| Galvanized steel pipe line post | Outside diameter 2 in | Depth 24 in in general soil | Runs needing a rigid line post |
| Fiberglass T line post | Cross section 1 in | Depth 12 to 18 in | Temporary and electric lines |
| Fiberglass round line post | Diameter 0.75 in | Depth 12 to 18 in | Temporary and electric lines |
| Wood H brace post at corner or gate | Top diameter 6 in, length 7 to 8 ft | Depth 36 to 42 in | Corners, ends and gate openings |
| Wood in line pull post | Top diameter 5 in | Depth 36 to 42 in | Slope and alignment changes |
| Steel pipe brace post | Nominal 2 3/8 in, 7 lb per ft | Depth 36 in in a 12 in hole | Set in concrete |
| Horizontal compression brace | Wood diameter 4 in | Length 8 ft minimum | Between the two H brace posts |
Source: USDA Natural Resources Conservation Service, North Carolina, Conservation Practice Specification: Fencing, Code 382, Materials and Construction Specifications.
The specification is written for agricultural fence, and the soil logic carries straight over to panel fencing. Sand needs the deepest posts and shallow rock the least.
Common mistakes
- Ordering one post for every panel.
- A run of 14 bays has 15 post positions, because both ends of every bay need support and the two end bays do not share their outer post with anything. Take the post figure from the tool rather than copying the panel figure, and check it by counting stakes on the ground before the delivery is booked.
- Entering the panel width as the post spacing when the posts are slotted.
- Slotted concrete and steel posts add their own thickness to each bay, so the true center to center spacing is wider than the panel and the run holds fewer bays. Measure a post, add its thickness to the panel width, and enter that as the spacing. Moving the spacing from 1.8 m to 1.9 m drops a 24 m run from 15 posts to 14.
- Assuming the 5 percent allowance always buys another panel.
- Rounding up happens after the allowance, so on many runs the allowance is absorbed by the rounding and adds nothing at all to the delivered quantity. Compare the run with and without the allowance. At 24 m and 1.8 m panels both give 14, while at 25.2 m the allowance is what pushes the order from 14 to 15.
- Measuring a sloping boundary as if it were level.
- A tape held horizontally reports the plan length, but panels and posts follow the ground, so the material has to cover the longer sloping distance instead. Measure along the slope or add the fall into the calculation. A 24 m plan length on a 10 percent grade is about 24.12 m on the ground and needs 15 panels.
- Applying the waste percent to the post quantity as well.
- Posts are not cut to fit, so there is no offcut to allow for. Padding the post count buys spare stock rather than covering a measurable loss in the material. Leave the allowance on the panels only, then add spare posts as a deliberate decision if the ground is rocky and a post may be broken during driving.
When a boundary fence becomes a regulated barrier
Height and location decide whether a fence is a garden job or a code job. Model building code language exempts fences from a permit up to 7 feet, or 2134 mm, with swimming pool barriers written out of that exemption. If the fence encloses a pool, the numbers tighten sharply. The barrier must stand at least 48 in, or 1219 mm, above grade on the side facing away from the water. The gap at grade cannot exceed 2 in, or 51 mm. No opening may pass a 4 in sphere. Where horizontal members sit less than 45 in apart, vertical members can be no more than 1.75 in apart, and where they sit 45 in or more apart, that widens to 4 in. Chain link mesh is capped at a 2.25 in square. The gate release goes on the pool side at least 3 in below the top of the gate, with no opening larger than 0.5 in within 18 in of it. None of that changes the panel count. It changes which panel you are allowed to buy.
Frequently asked questions
Why does the tool return more posts than panels?
Panels fill the gaps between posts, and a straight run has one more post position than it has gaps. The tool divides the run by the post spacing, rounds up to whole bays, then adds one for the far end. On the 24 m example that is 14 bays and 15 posts. The difference is always exactly one on a straight leg, and it disappears at a corner, where two legs share a single post.
Does the waste percent apply to the posts too?
No. The allowance only multiplies the panel figure, because panels are the item that gets trimmed, cracked in handling or wasted at a short final bay. A post is either used whole or replaced whole. If you want spare posts for rocky ground where driving can split a post, add them as a separate line on the order rather than raising the percentage.
How deep should the posts go?
The tool does not set depth, so use the published fence specification instead. It calls for at least 24 in of setting depth for a 3.5 in wood line post in general soil, 18 in where rock is shallow, and 30 in in sand. Corner, end and gate posts move up to 36 to 42 in and a larger diameter, since they carry the pull of the whole run rather than the load of one bay.
What changes when the run includes a gate?
Subtract the finished gate opening from the run before you calculate, because the opening is a hardware dimension and never matches a panel width. Then treat the two gate posts as braced posts rather than line posts. The published specification allows a gate under 100 lb to hang from a single well set end post, and sends heavier gates or openings wider than 6 ft to a braced assembly.
Is a livestock fence calculated the same way?
The counting is the same but the product is not. Agricultural wire fence is specified by wire height and spacing rather than panel width. One wildlife friendly standard caps the top wire at 44 in with the top two wires 10 to 12 in apart, and offers 39 in of woven wire with two barbed strands at 2 in and 3 in above it for the same 44 in total height.
Sources
- Conservation Practice Specification: Fencing, Code 382, Materials and Construction Specifications USDA Natural Resources Conservation Service, North Carolina. Source of every figure in the post table and of the 24, 18 and 30 in setting depths, the 6 in oversize hole, the 4 in backfill layers, the 24 hour concrete rule and the 100 lb gate limit. Accessed 2026-09-07.
- 2012 International Residential Code, Appendix G Swimming Pools, Spas and Hot Tubs International Code Council. Historical model-code source for the pool barrier limits quoted on this page: 48 in height, 2 in gap at grade, the 4 in sphere, the 1.75 in and 4 in member spacings, 2.25 in mesh and the gate release rules. Local adopted rules must be checked separately. Accessed 2026-09-07.
- 2015 International Residential Code Section R105.2, Work Exempt From Permit International Code Council. Supports the statement that model code language exempts fences up to 7 feet, or 2134 mm, from a building permit while writing pool barriers out of that exemption. Accessed 2026-09-07.
- Conservation Practice Standard: Fence, Code 382, New Mexico supplement USDA Natural Resources Conservation Service, New Mexico. Supports the wildlife friendly wire figures in the livestock answer: a 44 in top wire, the top two wires 10 to 12 in apart, and 39 in of woven wire with barbs at 2 in and 3 in. Accessed 2026-09-07.
Related calculators
This is a planning result, not a supplier quote; sellers use different pack, bag, board, roll, and bundle conventions, so confirm the exact product label and selling unit before you order.