# Steelwork Paint Calculator

Tonnage to surface area to paint quantity for protective coating.

- Page: https://jianzhujisuan.com/en/steel-paint
- Category: Finishes (https://jianzhujisuan.com/en/c/finishes)
- Chinese version: https://jianzhujisuan.com/zh/steel-paint.md
- Data checked: 2026-10-25

## Quick result

With the default inputs (Steel tonnage 10 t, Area per tonne 28 m²/t, Number of coats 2 courses, Dry film per coat 60 μm, Volume solids 55%, Paint density 1.4 g/cm³, Loss factor 1.6 ×): **Paint to order 136.8 kg**

## Inputs

| Parameter | Type | Default | Unit | Note |
|---|---|---|---|---|
| Steel tonnage | number | 10 | t |  |
| Area per tonne | number | 28 | m²/t | Heavy plate 15-25, rolled sections 25-35, light purlins 40-55 |
| Number of coats | number | 2 | courses |  |
| Dry film per coat | number | 60 | μm | 120-150 μm total outdoors, 100-125 μm indoors |
| Volume solids | number | 55 | % | Zinc-rich epoxy 50-60%, alkyd 40-50%, fluorocarbon 55-65% |
| Paint density | number | 1.4 | g/cm³ |  |
| Loss factor | number | 1.6 | × | Brush 1.3-1.4, air spray 1.6-1.8, airless 1.4-1.6 |

## 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)

## Worked example

10 t of sections at 28 m²/t, two 60 μm coats, 55% volume solids, density 1.4 and a 1.6 loss factor: 280 m², 85.53 kg theoretical, 136.8 kg to order, 13.7 kg per tonne.

## Questions

### What is the right area-per-tonne figure?

Best is to total the member surface areas from the take-off, or sum section perimeters times lengths. For estimates, use bands by member type: H-section columns and beams 25-30 m²/t, angle and channel trusses 30-40, cold-formed purlins 45-55, heavy plated members (box columns, deep beams) 15-22. Picking the wrong band doubles or halves the paint.

### Volume solids or weight solids?

Volume solids is how much solid volume remains after drying and it alone sets the film thickness — you buy paint by volume and deliver by thickness, so volume solids is what the calculation needs. Weight solids depends on pigment density, is used for VOC, and cannot give film build. The two typically differ by ten points or more; using the wrong one leaves you short.

### How is dry film thickness controlled?

On site, use a wet film gauge in real time: wet = dry ÷ volume solids, so a 60 μm dry film at 55% solids needs about 110 μm wet. After curing, test with a magnetic gauge at several points per member, taking mean and minimum — the minimum must not fall below 80% of spec and at least 85% of readings must meet it. Too thin kills durability, too thick cracks.

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