Steelwork Paint Calculator
Tonnage to surface area to paint quantity for protective coating.
With the default inputs: Steel tonnage 10 · Area per tonne 28 m²/t · Number of coats 2 courses etc.Paint to order 136.8 kg
Edit the inputs below to recalculate.Inputs
Result
| Painting area | 280.0m² |
| Total dry film | 120μm |
| Theoretical quantity | 85.53kg |
| With loss | 136.84kg |
| Per square metre | 0.489kg/m² |
| Per tonne of steel | 13.68kg/t |
| Drums at 20 kg | 7cans |
Area per tonne is the crux here: thinner sections carry more surface per tonne of steel. Rolled sections sit around 25-35 m²/t, heavy plate sections only 15-25 m²/t, and light purlins or space frames reach 40-55 m²/t. Theoretical quantity is kg = area × DFT(μm) × density ÷ (1000 × volume solids). Use volume solids, not weight solids — the two differ a lot. The loss factor covers overspray, drum residue and touch-up.
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Enter a target result; the other inputs stay fixed and this one is worked out.
Formula
| Painting area | A = tonnage × area per tonne |
| Theoretical quantity | G = A × total DFT × density ÷ (1000 × volume solids) |
| Actual quantity | G = theoretical × loss factor |
| Per tonne | g = actual ÷ tonnage (kg/t) |
How to work it out
- Establish the developed area: steel weight × area per tonne. Hot-rolled sections run 25-40 m²/t, H-sections 28-35, tube 20-25, platework 15-20, and lattice or truss work 40-60.
- Set the total dry film thickness from the protection class: 120-150 μm in ordinary atmospheres, 200-240 in industrial or coastal, split into primer, intermediate and finish.
- Convert dry to wet film: wet = dry ÷ volume solids. A 50% solids paint at 60 μm dry needs 120 μm wet.
- Compute paint mass: area × wet film (mm) × density (kg/L). Or directly: dry film mass = area × dry thickness × density, then divide by volume solids.
- Apply the loss factor: brush 1.15-1.3, roller 1.2-1.4, airless spray 1.5-2.0, at the top of the range for complex lattice and truss work.
Where it goes wrong
- Using the dry thickness as wet film — at 50% volume solids that halves the paint; it is the single most common error in the trade.
- Taking 1.1 as the loss factor universally — airless spray actually loses 1.5-2.0 and lattice work up to 2.5, so 1.1 guarantees running short.
- Ignoring the surface preparation grade — adequate paint on a St2 surface will not adhere and peels within a year; Sa2.5 is the floor for heavy protection.
- Accepting without measuring thickness — dry film must be checked with a magnetic gauge, three to five readings per square metre averaged; visual inspection proves nothing.
Material and cost
Zinc-rich epoxy primer 25-45 CNY/kg, epoxy micaceous iron oxide intermediate 20-35, polyurethane finish 30-60. Complete system including preparation, paint and labour 120-260 CNY/t, heavy duty 300-500.
On site
- Primer must go on within four hours of blast cleaning; beyond that the steel flash-rusts and must be reblasted. The clock is a hard requirement.
- Epoxy does not cure below 5 °C; in winter either shelter and heat or switch to a low-temperature grade.
- Respect both the minimum and maximum overcoating intervals — too soon and the solvent lifts the coat, too late and the surface must be abraded before the next coat.
Basis
- GB 50205-2020 Code for acceptance of steel structure construction, Chapter 13
- GB/T 8923.1-2011 Preparation of steel substrates, Part 1 (visual assessment of surface cleanliness)
- JGJ/T 251-2011 Technical specification for corrosion protection of building steel structures
FAQ
What is the right area-per-tonne figure?
Volume solids or weight solids?
How is dry film thickness controlled?
Cite this page
Use this format in reports, method statements or coursework. The link is permanent.
Building Calculator. Steelwork Paint Calculator. 2026-10-25. https://jianzhujisuan.com/en/steel-paint