What size air compressor do I need for sandblasting?
Size the nozzle first, then the compressor. Clemco’s published chart puts a 3/16 inch (5 mm) orifice at 45 cfm and a 1/2 inch (12.5 mm) orifice at 338 cfm, both measured at 100 psi at the nozzle. Those two nozzles need a blast line of 3/4 inch (20.00 mm) and 2 inch (50.00 mm) bore respectively.
That is the whole of sizing a compressor for sand blasting, one step inside the wider sand blasting process. The nozzle sets the demand, and the compressor, the air line and the blast hose all follow it. Work in the other direction, from whatever compressor is already on site, and you end up with a nozzle the machine cannot feed.
This page walks the chain in order, using figures published by Clemco Industries Corp. and Kennametal. Every number quoted from those charts is theirs. The bore column is ours.
Start at the nozzle, not the compressor
The orifice is the only part of a blast system that meters air. Everything upstream of it is plumbing. A 3/8 inch (9.5 mm) nozzle will pass the air a 3/8 inch nozzle passes, whatever compressor is behind it, and if the compressor cannot supply that volume the pressure at the nozzle simply falls until supply and demand meet.
That is why the order matters. Pick the nozzle for the work and the standoff you need, read its air demand off the manufacturer’s chart, then buy or hire a compressor with headroom over that figure, and only then size the line.
Kennametal states the headroom rule directly in its nozzle selection guide: “the air supply system should be able to provide at least 50% more air volume (cfm) than a new nozzle in order to develop the required working blasting pressure, whether that is 100 psi or 140 psi.” The reason is wear. An orifice opens up in service, and an open orifice eats more air.
How nozzle orifice size sets your CFM demand
Below is Clemco’s air consumption and compressor requirement at 100 psi at the nozzle, set against Clemco’s own minimum connector ID for the same orifice, and against the matching bore from the Flexihose sand blast hose range.
Drawn from the table below. Air demand and compressor HP read at the 100 psi column of Clemco Industries Corp., “Compressed-Air & Abrasive Consumption”; orifice and bore figures as printed there and in the Flexihose sand blast hose range. Circle areas follow from those diameters. No dimension is drawn that the table does not state.
| Nozzle | Orifice | Air at 100 psi (cfm) | Compressor (HP) | Clemco minimum connector ID | Flexihose bore |
|---|---|---|---|---|---|
| No. 3 | 3/16″ (5 mm) | 45 | 10 | 3/4″ (19 mm) | 3/4″ (20.00 mm) |
| No. 4 | 1/4″ (6.5 mm) | 81 | 18 | 1″ (25 mm) | 1″ (25.00 mm) |
| No. 5 | 5/16″ (8 mm) | 137 | 31 | 1-1/4″ (32 mm) | 1-1/4″ (31.00 mm) |
| No. 6 | 3/8″ (9.5 mm) | 196 | 44 | 1-1/2″ (38 mm) | 1-1/2″ (38.00 mm) |
| No. 7 | 7/16″ (11 mm) | 254 | 57 | 2″ (50 mm) | 2″ (50.00 mm) |
| No. 8 | 1/2″ (12.5 mm) | 338 | 75 | 2″ (50 mm) | 2″ (50.00 mm) |
Source: air and compressor HP columns from Clemco Industries Corp., “Compressed-Air & Abrasive Consumption”, read at the 100 psi column. Connector ID column from the same company’s “Minimum Connector ID by Nozzle Orifice Size” chart. Orifice and connector sizes are reproduced in Clemco’s own units and are not converted here. The Flexihose bore column is ours, taken from the sand blast hose range, and its millimetre figures are the catalogue’s own for that nominal inch size, which is why 1-1/4″ reads 31.00 mm here and 32 mm in Clemco’s column. Chart read 13 September 2026. Kennametal publishes an equivalent chart separately; it is not blended into this one.
Two things in that table are worth more than the rest of it.
The first is how fast the air demand climbs. Going from a No. 4 to a No. 6 nozzle, which is one step up in each of two sizes, takes the requirement from 81 cfm to 196 cfm. The compressor more than doubles, from 18 HP to 44 HP. Buyers who change nozzle size without changing anything else are the commonest version of this mistake.
The second is what happens as a nozzle wears. Clemco publishes that separately, and the figures are the same ones: a No. 4 that has worn out to a No. 5 profile consumes 69% more air than it did new. That is Clemco’s own figure, at 100 psi. It is also the reason Kennametal asks for 50% headroom rather than an exact match.
Kennametal publishes an equivalent chart in metric and imperial together, and its numbers sit within about 2% of Clemco’s at the same orifice and pressure. At 1/4 inch and 100 psi Clemco gives 81 cfm and Kennametal gives 80. At 1/2 inch, Clemco gives 338 and Kennametal 340. Two unconnected manufacturers arriving at the same figures is the best confirmation available in this category.
Both charts are their publishers’ own figures at their publishers’ own stated pressures, and Kennametal prints the caveat on its chart: “This table is to be used as reference only. Actual results may vary depending on specific abrasive medium used.” Check them against the data for the nozzle you actually own, and remember that a worn orifice consumes more air than its nominal size.
How do you check the hose bore against the nozzle?
Read the minimum connector ID column for your orifice and compare it with what is on the reel. Clemco’s chart is a lookup, not a rule of thumb, which makes it easier to argue with a supplier.
It is worth noting what that lookup actually works out at. Clemco’s own pairs run from 5 mm orifice against 19 mm ID up to 12.5 mm against 50 mm, which is close to four times the orifice, not three. The common trade shorthand of “three to four times” sits at the loose end of what Clemco publishes. If you are choosing between two bores, Clemco’s table points at the larger one.
Two limits are worth stating plainly. Above a 1/2 inch (12.5 mm) orifice, Clemco calls for 2-1/2 inch (64 mm) and 3 inch (76 mm) connector IDs, and those are above the top of this hose range, which ends at 2 inch (50.00 mm). And at the other end, the 1/2 inch (12.00 mm) bore in the range is not a blast line size for any nozzle on Clemco’s chart. It is there for other duties.
The abrasion-resistant sand blasting hose page carries the full bore ladder from 1/2 inch to 2 inch (12.00 to 50.00 mm), with working pressure at 175 PSI / 12 BAR and burst at 700 PSI / 48 BAR across every size. Blast work at 100 psi at the nozzle sits well inside that rating.
What happens when the blast hose is undersized?
The nozzle starves, and the loss is not proportional. Clemco publishes the internal area lost when a line steps down: from 2 inch (50 mm) to 1-1/4 inch (32 mm) loses 61% of the cross-sectional area. From 1-1/2 inch (38 mm) to 1 inch (25 mm) loses 56%. A step that looks like one size on paper is most of the flow path in practice.
What the operator sees is a slower cut. The abrasive still leaves the nozzle, so nothing looks broken, but the work takes longer and the hose itself wears faster because the same abrasive is moving through a tighter bore.
Abrasion resistance is the specification that decides how long that hose lasts. The Flexihose sand blast grade is built with an extra-thick seamless rubber lining free from mineral filler, and records a DIN abrasion loss below 60 mm3. It exceeds IS 5894 and is not BIS licensed, which is the correct way to state it.
Why is 7 bar at the pot not 7 bar at the nozzle?
Because every fitting, every bend and every metre of line between the two takes a share. Clemco quantifies the fittings, based on 100 psi (7 bar) in 1 inch (25 mm) pipe: a 90 degree pipe elbow costs 3 psi (0.2 bar / 21 kPa), a pipe tee costs 5 psi (0.3 bar / 34 kPa), and a swing check valve costs 18 psi (1.2 bar / 124 kPa). Put three elbows and a tee in a line and the gauge on the pot is already telling you a different story from the nozzle.
That matters because blast production is sensitive to nozzle pressure in a way most buyers underestimate. Kennametal publishes an efficiency factor against nozzle pressure, with 100 psi as the 100% baseline:
Drawn from the table below. Efficiency factor and abrasive velocity from Kennametal, “A Guide to Blasting Nozzle Selection”, which publishes both as estimates. Points are plotted at the published percentages; nothing between them is interpolated.
| Blast nozzle pressure | Estimated abrasive velocity | Estimated efficiency factor |
|---|---|---|
| 100 psi | 420 mph | 100% |
| 95 psi | 400 mph | 93% |
| 90 psi | 365 mph | 85% |
| 85 psi | 330 mph | 78% |
| 80 psi | 270 mph | 70% |
| 75 psi | 210 mph | 63% |
| 70 psi | 190 mph | 55% |
Source: Kennametal, “A Guide to Blasting Nozzle Selection”, PDF hosted by its distributor Canfield & Joseph. Figures reproduced in Kennametal’s own units, read 13 September 2026.
Read the 90 psi row. Losing 10 psi between the pot and the nozzle costs 15% of production, by Kennametal’s own table. At 80 psi you are doing 70% of the work for 100% of the diesel and 100% of the labour.
The line from the compressor to the pot is a separate sizing question from the blast hose, and it is usually the one people get wrong, because it looks like ordinary air plumbing. Clemco gives minimum air line ID by nozzle: a No. 6 (3/8 inch, 9.5 mm) nozzle wants 1-1/2 inch (38.0 mm) minimum. For that run we make a 20 bar industrial air hose, which is the right product for the compressor-to-pot leg. The blast hose is not.
Moisture, the separator, and why wet air ruins a blast finish
Compressed air carries water, and water and abrasive make a paste. Atlas Copco puts the mechanism plainly in its guidance on choosing a sandblasting compressor: “Moisture in compressed air causes abrasive clumping and nozzle blockages.” The same page adds that “Moisture removal by adding a dryer or moisture separator is also essential to prevent clogs and maintain consistent blasting performance.”
In practice the failure shows up as an intermittent blast, a pot that needs clearing, and a finish that varies across a panel because the media flow varied. It is frequently diagnosed as a bad nozzle or a bad batch of abrasive.
Atlas Copco also names the other half of the same problem: “Long hose runs, undersized piping, and fittings create pressure drop and restrict airflow. Keeping the distribution path short and properly sized helps maintain output.” Short, straight and correctly sized is the whole of it.
What to send us for a hose recommendation
We do not sell compressors, nozzles, pots or couplings. See the parts of a blast line for what each one does. We make the hose, so the recommendation we can give you is a bore, a construction and a length. To give it, we need four things:
- Nozzle orifice size, in inches or millimetres, and whether it is new or part worn.
- Compressor output in cfm, and its rated pressure.
- Blast pressure you are working at, measured at the nozzle if you have the reading.
- Length of line you need, and how many couplings are in it.
With those four we can tell you which bore in the range fits, and where your own numbers disagree with the charts above. If the compressor cannot hold the nozzle’s demand at working pressure, we will tell you that too, because a larger hose will not fix it.
The full specification, including the bore ladder, the 175 PSI / 12 BAR working pressure, the -40 C to +75 C service range and the construction, is on the sand blast hose specification page. Enquiries for India go to +91 80940 02348.
↑ Back to topFAQ
What size compressor do I need for a 3/8 inch blast nozzle?
Clemco's published chart puts a 3/8 inch (9.5 mm) orifice at 196 cfm and 44 HP, measured at 100 psi at the nozzle. Kennametal advises sizing the supply at least 50 percent above what a new nozzle needs, so that pressure holds as the orifice wears open. Those two figures together are the safe way to specify.
What hose bore does a 1/4 inch blast nozzle need?
Clemco lists a 1 inch (25 mm) minimum connector ID for a 1/4 inch (6.5 mm) orifice. In the Flexihose sand blast range that is the 1 inch (25.00 mm) bore. Going a size under starves the nozzle and costs blast pressure at the workface.
Is a bigger blast hose always better?
Up to the top of the range, a larger bore never hurts flow, and where Clemco's table sits between two sizes it points at the larger one. Beyond that it stops helping, because the nozzle is still the restriction. This grade runs from 1/2 inch to 2 inch (12.00 to 50.00 mm) and 2 inch is the largest bore made.
What pressure should I be blasting at?
Kennametal's efficiency table uses 100 psi at the nozzle as its 100 percent baseline. At 90 psi the same table gives 85 percent, and at 80 psi it gives 70 percent. Measure at the nozzle, because the reading at the pot is always the higher of the two.
Why does the blast slow down when the compressor gauge still reads full?
Because the gauge is at the pot and the work happens at the nozzle. Clemco costs a 90 degree pipe elbow at 3 psi (0.2 bar / 21 kPa) and a swing check valve at 18 psi (1.2 bar / 124 kPa), based on 100 psi in 1 inch (25 mm) pipe. Fittings, bends and line length take their share before the air reaches the nozzle.
Can I use the same hose from the compressor to the blast pot?
No. That leg carries clean compressed air and is sized as an air line, not as a blast line. Flexihose makes a separate 20 bar industrial air hose for it. The sand blast grade is built for abrasive moving against the bore, which is a different duty.
What length of blast hose do you supply?
Standard supplied coil length is 40 metres, across the full 1/2 inch to 2 inch bore range. Send the run length you need along with your nozzle size and compressor output, and the works will confirm what can be supplied in that bore.
Is the Flexihose blast hose BIS certified?
No. It exceeds IS 5894 and carries no BIS licence, and those are different claims. Three Flexihose products are BIS licensed: Water Hose Type 2, Air Hose Type 1 and Air Hose Type 2. Anything else citing an IS number exceeds that standard rather than conforming to it.
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