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Free fencer calculator
Fence calculator: panels, posts, gravel boards and postcrete
Enter the run and height of the fence, pick panels, closeboard or post and rail, and find out how many panels or boards, posts, rails, gravel boards and bags of postcrete to order. Bays and post spacing follow Jacksons, AWBS and tradecalculator; postcrete follows the Blue Circle datasheet at two bags a post; and it warns you when the fence goes over the 2m planning limit.
What you need
Bays and posts
- Bays
- 7 bays12.0m at 1.83m each; the last bay is usually a cutJacksons: panels 1.83m
- Timber posts (100 × 100mm)
- 8 × 2.7mone more than bays. 1.8m fence + 600mm in the ground + 150mm gravel board, rounded up to stock lengthsBlue Circle: hole a third of the height above ground; tradecalculator: 600 minimum, 900 exposed
- Postcrete
- 16 × 20kg bags2 per post. 300 × 600mm holesBlue Circle Postcrete: 2 bags at 300 × 600, 3 at 750 deep
- Or site-mixed concrete
- 0.32 m³0.04m³ per holetradecalculator: 300ø × 600 less the post ≈ 0.036m³
Panels and rails
- Fence panels
- 7 × 1.83m panels
- Gravel boards (150mm)
- 7 × 1.83mtimber or concreteHowarth: 150 and 305mm concrete boards
Fixings
- Panel clips or U-brackets
- 28 clips4 per panel; slotted concrete posts need none
- Gravel board clips
- 14 clips
- Post caps
- 8 caps
Sundries
- Fence treatment
- 8 litresboth sides at 6m² per litre on rough-sawn timber
Planning
- Planning
- 1.95m total: no permission needed unless next to a highway (1m max) or on a listed building Planning Portal
Round up to whole packs and bags. Figures include the wastage you chose and match TradeCalc in the app.
For fencers: turn this into a quote
In the app, TradeCalc hands these quantities straight to ProQuote with your regional material prices, and the customer gets a branded PDF. Free to download.
Or claim your free profile link nowHow the maths works
- Bays are the run divided by the bay width, rounded up. Panels are 1.83m (Jacksons); closeboard built on site is 2.4m bays (most common) or 3m (the AWBS standard and the maximum for an arris rail); post and rail is 1.8m. You need one more post than bays, plus one for every corner. Gate posts are counted on top.
- Post length is the fence height plus 600mm in the ground, or 900mm on an exposed or soft site, plus the gravel board, rounded up to the stock lengths (2.4m, 2.7m, 3.0m). A 1.8m fence with a 150mm gravel board needs a 2.7m post, the trade's 9ft post for a 6ft fence.
- Postcrete is two 20kg bags per post for a 100 × 100mm post in a 300 × 600mm hole (Blue Circle datasheet), three for a 750 to 900mm hole, a slotted concrete post or a gate post. Or about 0.04m³ of site-mixed concrete per hole.
- Closeboard uses featheredge at a 25mm lap: 13.3 boards a metre at 100mm, 10 at 125mm, 8 at 150mm, plus 10% for splits (tradecalculator). Arris rails are 2 per bay up to 1.5m and 3 at 1.5m and over, in bay lengths. Capping and counter rail run the length. Nails are 2 per board per rail, given in kilos at roughly 275 a kilo.
- Post and rail uses 3.6m rails that span two 1.8m bays, 3 high up to 1.2m and 4 above, so the rail count is the run divided by 3.6 times the rails high, not rails per bay.
- Gravel boards are one per bay, 150mm or 300mm. Timber posts take 4 panel clips a panel, 2 gravel board clips a bay and a cap each; slotted concrete posts need none of those. Treatment is both sides at 6m² per litre.
- A fence over 2m including the gravel board and any trellis needs planning permission, and 1m is the limit next to a highway (Planning Portal). The calculator warns you when the total goes over.
Worked example
A 12m run of 1.8m panels is 7 bays and 8 posts. With a 150mm gravel board and 600mm in the ground the posts are 2.7m long, and you need 7 panels, 7 gravel boards, 16 bags of postcrete, 28 panel clips, 8 post caps and 8 litres of fence treatment. At 1.95m overall it stays under the 2m planning limit.
Questions people ask
How many fence panels do I need?
Divide the run by 1.83m and round up. A 12m run is 7 panels, with the last bay usually a cut panel. You need one more post than panels, plus one for every corner. Gate openings are not part of the run: each gate gets two heavier posts of its own.
How deep should fence posts go?
600mm is the minimum for a 1.8m fence, and the Blue Circle rule is a hole a third of the height above ground and three times the post width. Go to 900mm on an exposed site or soft ground and 750mm for gate posts. So a 1.8m fence with a gravel board needs a 2.7m post, or 3.0m on an exposed site.
How many bags of postcrete per post?
Two 20kg bags for a 100 × 100mm post in a 300mm wide, 600mm deep hole, from the Blue Circle Postcrete datasheet; a 250mm hole takes 1⅓ and a 750mm deep hole 2¾, so call it three. Slotted concrete posts and gate posts need the bigger hole and three bags. Postcrete sets in minutes, so do one hole at a time.
Timber or concrete posts?
Timber posts look better and take clips, caps and screws, but rot at ground level in 10 to 15 years. Slotted concrete posts last far longer, the panels and concrete gravel boards just drop into the slots with no clips, but they are heavy, need a bigger hole and three bags of postcrete, and you cannot fix anything to them.
How many arris rails for a closeboard fence?
Two per bay up to 1.5m high and three at 1.5m and over, so a 1.8m closeboard fence has three. Rails come in 2.4, 3.0 and 3.6m, and 3m is the longest bay you should run them over. Add a capping rail and a counter rail along the top.
How high can a garden fence be?
Up to 2m at the back and sides without permission in most cases, and 1m next to a road (Planning Portal). The gravel board and any trellis count towards the height, so a 1.8m panel on a 300mm concrete gravel board is 2.1m and needs permission; on a 150mm board it is 1.95m and does not.
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