Free tool · Finishes
Paint and Galvanising Area Calculator
Surface area of steel for painting, galvanising and intumescent coating: m² per metre, section factors, and totals for a whole list.
Quick answer
Surface area to coat = m² per metre × length × number of pieces. For example, a 457 × 191 × 67 UB has 1.63 m² per metre on all sides, or 1.44 m² per metre on 3 sides when a slab covers the top flange (A/V 191 and 169 m⁻¹). The Koyda calculator gives the area per metre for every UK beam, column, channel, angle, hollow section, flat and round bar, and totals m² and tonnes for a list.
Cite this: Koyda Ltd, “Paint and Galvanising Area Calculator”, https://www.koyda.com/steel-paint-area-calculator/, reviewed 10 October 2026.
Area calculator
Add sections to build a list. It is saved on this device.
| Section | Length × pcs | m²/m | m² | kg | Remove |
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Paint estimate (optional)
From your paint's product data sheet. Theoretical spreading rate = volume solids % × 10 ÷ dry film thickness.
Typical losses from coating suppliers: about 10–15% brush or roller, 30–50% spray. Check the data sheet and your applicator.
Nominal areas for new, unprimed steel. They exclude cleats, plates, bolts and fittings: allow extra for connections. Intumescent thickness comes from your fire protection supplier.
Use the tables and calculator offline
Install the Koyda app: section tables, weight calculator, CSV and PDF downloads, even without signal on site.
How it works
Where the figures come from
- UB, UC and PFC: area per metre and A/V from the SCI Steel for Life Blue Book (P363). Three sizes not in it use the British Steel dimensions.
- SHS, RHS and CHS: hot-finished (BS EN 10210) areas from the Blue Book. Cold-formed tubes have larger corners and slightly less area.
- Angles: 2 × (a + b) less the rounding at the root and toes. Checked against British Steel's 0.47 m²/m for 120 × 120 × 8.
- Flats: 2 × (width + thickness). Rounds: π × diameter.
- 3 sides: all sides less the top face, for beams and box sections under a slab.
Questions
Frequently asked questions
How is the surface area worked out?
For beams, columns, channels and hot-finished hollow sections the area per metre is the published figure from the SCI Steel for Life Blue Book (P363). Angles use their root and toe radii; flats are 2 × (width + thickness) and rounds π × diameter. Multiply by the length and the number of pieces for the total.
What does '3 sides' mean?
A beam that supports a slab or deck has its top face covered, so only three sides need intumescent paint or fire board. The 3-sided area leaves out the top of the top flange (or the top face of a box section). Angles, channels, tubes, flats and rounds use the all-sides figure.
What is the A/V or section factor?
A/V (also Hp/A) is the heated perimeter divided by the cross-section area, in m⁻¹. Intumescent and board suppliers use it with the fire period and the critical temperature to set the coating thickness. Higher A/V means a thinner section that heats faster and needs more protection. Your fire protection supplier confirms the thickness.
How much paint do I need?
Theoretical spreading rate (m²/L) = volume solids % × 10 ÷ dry film thickness (µm), from the paint's data sheet. Divide the area by it and add a loss allowance: coating suppliers suggest about 10 to 15% for brush or roller and 30 to 50% for spray. Use the paint estimate in the tool with the figures from your product data sheet.
Does galvanising use area?
Galvanisers usually price by weight (per tonne), so the tool gives tonnes too. The m² per tonne shows how much surface each tonne carries: light sections have more.
Related tools
Related
- Steel Quote Builder: shows the coating area for your schedule
- Intumescent paint and fire protection
- Galvanising, powder coating and duplex
- RAL colour finder
- Steel weight calculator
Reference only
Nominal areas from published section data. Coating systems, thicknesses and quantities must come from the coating manufacturer or your fire engineer. Koyda Ltd accepts no liability for decisions based on these figures.
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