Steel Base Plate Sizes & Weights (Chart)
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Steel base plates are usually square, from 100 x 100mm up to 400 x 400mm, and 6mm to 20mm thick. The right size depends on the post or column you're fixing, the bolts you're using and the load. This guide lists the sizes we stock with their weights, plus a weight chart for every common size.
Weights are calculated for mild steel at 7,850 kg/m³ (stainless 7,930 kg/m³), with bolt holes deducted where the plate has them. Actual weights vary slightly with mill tolerance.
Base plates we stock
Click any size for the current price. Small plates ship free Australia-wide.
| Size | Thickness | Holes | Weight |
| 150 x 150mm | 6mm | No holes | 1.06 kg |
| 150 x 150mm | 10mm | No holes | 1.77 kg |
| 150 x 150mm | 12mm | No holes | 2.12 kg |
| 200 x 200mm | 6mm | No holes | 1.88 kg |
| 200 x 200mm | 6mm | 4 x 12mm holes, 160mm centres (M10) | 1.86 kg |
| 200 x 200mm | 10mm | No holes | 3.14 kg |
| 200 x 200mm | 10mm | 4 x 14mm holes, 150mm centres (M12) | 3.09 kg |
| 200 x 200mm | 12mm | No holes | 3.77 kg |
| 200 x 200mm | 12mm | 4 x 18mm holes, 160mm centres (M16) | 3.67 kg |
| 250 x 250mm | 10mm | No holes | 4.91 kg |
| 250 x 250mm | 10mm | 4 x 14mm holes, 200mm centres (M12) | 4.86 kg |
| Stainless 100 x 100mm | 10mm | 4 x 14mm holes, 60mm centres (M12) | 0.74 kg |
| Stainless 200 x 200mm | 5mm | 4 x 14mm holes, 150mm centres (M12) | 1.56 kg |
| Stainless 200 x 200mm | 10mm | 4 x 14mm holes, 150mm centres (M12) | 3.12 kg |
Most 200 x 200mm plates are also sold in sets of 4. See current prices across the full steel base plates range.
Steel base plate weight chart (kg)
Weight of a solid square mild steel plate with no holes. A 14mm bolt hole in a 10mm plate removes only about 12 grams, so holes make little difference.
| Size (mm) | 5mm | 6mm | 8mm | 10mm | 12mm | 16mm | 20mm | 25mm |
| 100 x 100 | 0.39 | 0.47 | 0.63 | 0.79 | 0.94 | 1.26 | 1.57 | 1.96 |
| 150 x 150 | 0.88 | 1.06 | 1.41 | 1.77 | 2.12 | 2.83 | 3.53 | 4.42 |
| 200 x 200 | 1.57 | 1.88 | 2.51 | 3.14 | 3.77 | 5.02 | 6.28 | 7.85 |
| 250 x 250 | 2.45 | 2.94 | 3.93 | 4.91 | 5.89 | 7.85 | 9.81 | 12.27 |
| 300 x 300 | 3.53 | 4.24 | 5.65 | 7.06 | 8.48 | 11.30 | 14.13 | 17.66 |
| 350 x 350 | 4.81 | 5.77 | 7.69 | 9.62 | 11.54 | 15.39 | 19.23 | 24.04 |
| 400 x 400 | 6.28 | 7.54 | 10.05 | 12.56 | 15.07 | 20.10 | 25.12 | 31.40 |
How to work out the weight of any steel plate
Weight (kg) = length (m) x width (m) x thickness (mm) x 7.85
For example, a 200 x 200 x 10mm plate is 0.2 x 0.2 x 10 x 7.85 = 3.14 kg. A 150 x 150 x 6mm plate is 0.15 x 0.15 x 6 x 7.85 = 1.06 kg.
Common sizes and what they're used for
| Plate size | Typical use |
| 100 x 100mm | Small posts, balustrades, handrails, letterboxes, signs |
| 150 x 150mm | Fence and gate posts, pergola posts, light frames |
| 200 x 200mm | Carport and verandah posts, deck posts, light steel columns |
| 250 x 250mm | Heavier posts and columns, larger bolts |
| 300mm and up | Structural columns, usually to an engineer's design |
Choosing the right base plate
- Size: the plate needs to be bigger than the post or column, with room for the bolts outside it. For a 75mm or 90mm square post, a 150mm or 200mm plate is typical.
- Thickness: 6mm suits light, non-structural work. 10mm to 12mm is the most common for posts and columns. Go thicker for heavy loads or larger bolts.
- Holes and bolts: match the hole size to your anchor bolts (14mm holes suit M12 bolts, 18mm holes suit M16) and keep the holes far enough from the edge.
- Mild or stainless: mild steel is cheaper and can be galvanised or painted. Stainless won't rust, so it suits coastal and exposed sites.
- Structural work: for load-bearing columns, always follow your engineer's or builder's specification.
Need a size we don't list, extra holes or a different thickness? Contact us for a quote on a custom-cut plate.