Estimate sandblasting time, abrasive media, and project cost from surface area, condition, and blasting setup, plus compressor CFM needs.
Sandblasting Formula
The calculator works in two modes. Project mode estimates time, abrasive, and cost from surface area. Nozzle air mode sizes a compressor from nozzle and pressure.
Area_est = Area_base × (1 + allowance) Time = Area_est ÷ ProductionRate Media = Area_est × MediaUse × SurfaceFactor Cost = Area_est × Price/sqft (or Media × $/lb for DIY)
- Area_base — raw surface area in sq ft (L×W for flat, π×D×L for pipe/tank outside)
- allowance — waste/overlap factor (0.10 typical, up to 0.20 complex)
- ProductionRate — sq ft per hour for the surface condition
- MediaUse — lb of abrasive per sq ft for the chosen media
- SurfaceFactor — multiplier for media consumption by surface (1.25 heavy rust, 0.65 wood, etc.)
CFM_demand = CFM_base × PressureFactor × WearFactor CFM_compressor = CFM_demand × 1.25
- CFM_base — nozzle air consumption at 100 psi
- PressureFactor — scales linearly with pressure (0.62 at 60 psi, 1.20 at 120 psi)
- WearFactor — 1.0 new, 1.2 slightly worn, 1.5 badly worn
- 1.25 — reserve margin so the compressor isn't run at 100% duty
Production rates and media use are field averages. Real numbers vary with operator skill, nozzle size, and air supply. Use the result as a planning estimate, not a fixed quote.
Reference Tables
Typical production rates and abrasive use by surface:
| Surface | Rate (sq ft/hr) | Contractor $/sq ft |
|---|---|---|
| Light rust / old paint | 75 | $2–$4 |
| Heavy rust / mill scale | 35 | $4–$8 |
| Concrete prep | 150 | $2–$3.50 |
| Wood restoration | 20 | $3–$6 |
| Fine detail | 15 | $6–$12 |
Nozzle air demand at 100 psi (multiply by pressure factor for other pressures):
| Nozzle | CFM @ 100 psi | Compressor (with 25% reserve) |
|---|---|---|
| 1/8 in (#2) | 20 | 25 CFM |
| 3/16 in (#3) | 45 | 56 CFM |
| 1/4 in (#4) | 81 | 101 CFM |
| 5/16 in (#5) | 137 | 171 CFM |
| 3/8 in (#6) | 196 | 245 CFM |
| 7/16 in (#7) | 254 | 318 CFM |
| 1/2 in (#8) | 338 | 423 CFM |
Worked Example & FAQ
Example: A 25 ft × 20 ft steel deck (500 sq ft) with heavy rust, blasted with coal slag, 10% allowance.
- Area_est = 500 × 1.10 = 550 sq ft
- Time = 550 ÷ 35 = 15.7 hours
- Media = 550 × 1.2 × 1.25 = 825 lb (17 bags)
- Contractor cost = 550 × $4 to $8 = $2,200–$4,400
Why does worn nozzle matter so much? A 1/4 in nozzle worn to 5/16 in passes about 70% more air at the same pressure. The compressor stays the same, so pressure drops and production falls. Replace nozzles when bore grows 1/16 in.
Does pressure really change rates? Yes. Dropping from 100 to 80 psi cuts production roughly in half. Hold 95–100 psi at the nozzle for efficient blasting.
How much abrasive should I buy? Round up to whole 50 lb bags and add a spare bag for setup loss and touch-ups.
