Fencing calculator
Work out how many fence panels and posts you need. Enter the total length of the run and the panel width and this calculator gives you the panels, posts, postmix and gravel boards.
Fencing calculator
Enter your measurements in metres. Everything updates as you type, and nothing is sent anywhere.
Standard fence panels are 1.83m (6ft) wide. You need one more post than panels, since there is a post at each end. Postmix is estimated at about two 20kg bags per post. Gravel boards and post caps are optional, one of each per panel and post.
How to measure a fence run
Measure along the line the fence will follow, not across the garden in a straight line, and measure at ground level. A run that climbs a slope is longer than the map distance, and on anything but a gentle gradient you will be stepping the panels down rather than following the slope, so each step needs its own post.
Treat every corner as the end of one run and the start of another. A garden fenced on three sides is three runs, and each one needs a post at both ends, so measuring the whole perimeter as a single length will under-order posts. Enter each run separately and add the results together.
Leave out gates and gate posts. Gate posts carry a swinging load and are usually heavier than fence posts, often set in concrete rather than postmix, so price and order those on their own.
Panel widths, and runs that do not divide evenly
Standard UK fence panels are 1.83m wide, which is the old 6ft. You will also find 1.5m and 0.9m panels, and close-board panels are sometimes made to order at whatever width suits the run. Set the panel width in the calculator to whatever you are actually buying, because a 1.5m panel across a 20m run needs three more panels and three more posts than a 1.83m one.
Almost no run divides exactly into whole panels. You have two options and they cost different amounts. Cutting the last panel down is the usual choice: order the rounded-up number the calculator gives you and trim one panel on site, which works cleanly with close-board and waney-edge but can look obvious with a framed lap panel. Alternatively, spread the shortfall by reducing the gap on several bays, which only works if you are building the fence board by board rather than dropping panels between posts.
The calculator rounds panels up, because a part panel still has to be bought whole.
Posts: how many, how long and how deep
You always need one more post than you have panels, because there is a post at each end of the run as well as one between every pair of panels. This is the single most common ordering mistake, and it is why a 10-panel fence takes 11 posts.
Set posts at least 600mm into the ground for a 1.8m fence, and deeper on an exposed or windy site. That means the post itself has to be the fence height plus the depth in the ground, so a 1.8m fence on 600mm foundations needs 2.4m posts. Order the length, not the height.
For timber posts, 100mm by 100mm is standard for a 1.8m fence and 75mm by 75mm is enough for a low boundary. Concrete posts cost more and are heavier to handle, but they do not rot at ground level, which is where almost every timber fence fails first. If you are replacing a fence because the posts went and the panels are sound, concrete posts or concrete repair spurs are worth the extra.
Postmix, gravel boards and the rest
The calculator allows about two 20kg bags of postmix per post, which suits a 100mm post in a 300mm wide hole at 600mm deep. Taller fencing, wider holes or looser ground take more, so buy a spare bag or two rather than stopping halfway. Postmix sets in minutes and cannot be kept once mixed, so mix it hole by hole.
Gravel boards sit under the panel and keep the timber off wet soil. They are optional, and they are the cheapest thing you can do to make a fence last, because a panel sitting in damp earth will rot years before one that is not. One board per panel. Post caps do the same job at the top of the post and there is one per post.
For what the finished job costs, fitted, see the fencing cost guide. This page works out what to order, not what to pay.
Common questions
How many fence panels and posts do I need?
Divide the total length of the fence by the panel width, usually 1.83m, and round up for the number of panels. You need one more post than panels, because there is a post at both ends as well as between each panel.
How much postmix do I need per fence post?
About two 20kg bags of postmix per post for a standard 1.8m fence, more for taller or exposed fencing where the posts are set deeper. Set posts at least 600mm into the ground.
How long should fence posts be for a 1.8m fence?
2.4m. A 1.8m fence needs at least 600mm of post in the ground, so the post has to be the fence height plus the depth of the hole. Buying 1.8m posts for a 1.8m fence is a common and expensive mistake.
What if my fence length does not divide into whole panels?
Order the rounded-up number of panels and cut the last one down on site. That is the normal approach and it works well with close-board and waney-edge panels. If you are building board by board you can instead narrow several bays slightly and spread the shortfall across the run.
Do I need gravel boards?
They are optional but worth it. A gravel board holds the panel clear of wet soil, and ground contact is where most timber fences rot first. Allow one board per panel. They also let you replace the board rather than the whole panel later.
Are concrete or timber fence posts better?
Concrete posts cost more and are much heavier to handle, but they do not rot at ground level, which is where nearly every timber fence fails. If you are replacing panels that are still sound because the posts have gone, concrete posts or concrete spurs will outlast a second set of timber ones.
These quantities are a guide to help you order. Always round up and check with your supplier before buying.