Air Compressor Size Calculator: CFM, HP and BAR
Enter the air your machines use and the pressure they need. The calculator adds an allowance for leaks and growth, picks the pressure rating, and shows the Karan Micro Industries compressor that delivers it, using the model tables on our product pages.
How the calculator sizes a compressor
- Add up the air. Total the CFM of every machine that can run at the same time.
- Add an allowance. Multiply by 1.1–1.2 for leaks and future growth, Atlas Copco's rule of thumb (20% is the default here).
- Set the pressure. Take the highest pressure any machine needs and add about 1 bar for the dryer, filters and piping. The calculator then uses the lowest pressure rating in the tables at or above that figure (8, 10, 13 or 16 kg/cm², treating kg/cm² and bar as equal; 1 kg/cm² is 0.98 bar).
- Pick the model. It shows the smallest Karan model that delivers your total at that pressure, and splits very large demand across two or more units.
How many CFM per HP?
On Karan Micro Industries' KCS rotary screw compressors, 1 HP gives about 3.8–4.8 CFM at 8 kg/cm², and less at higher pressure. Always compare machines on CFM at your working pressure, not on HP.
| Model | HP | 8 kg/cm² | 10 kg/cm² | 13 kg/cm² | 16 kg/cm² |
|---|---|---|---|---|---|
| KCS-05 | 5 | 19 | 17 | 15 | – |
| KCS-7.5 | 7.5 | 29 | 26 | 23 | – |
| KCS-10 | 10 | 39 | 32 | 30 | – |
| KCS-15 | 15 | 59 | 47 | 45 | – |
| KCS-20 | 20 | 80 | 65 | 59 | 45 |
| KCS-25 | 25 | 108 | 92 | 74 | – |
| KCS-30 | 30 | 129 | 107 | 91 | 83 |
| KCS-40 | 40 | 164 | 150 | 140 | – |
| KCS-50 | 50 | 222 | 200 | 173 | – |
| KCS-60 | 60 | 286 | 268 | 220 | – |
| KCS-75 | 75 | 357 | 303 | 283 | – |
| KCS-100 | 100 | 464 | 389 | 353 | – |
| KCS-150 | 150 | 724 | 618 | 572 | – |
Two-stage KST screws deliver 205–786 CFM, and two-stage KC reciprocating compressors 7.8–80 CFM free air delivery at 12.3 kg/cm². For 25–45 BAR, as in PET bottle blowing, see the booster and high-pressure ranges.
Frequently Asked Questions
Straight answers from our engineers, last reviewed October 2026. Click a question to see the answer.
Ask our engineers01How do I calculate the CFM my plant needs?
Add the CFM of every machine that can run at the same time, then add 10–20% for leaks and growth, Atlas Copco's rule of thumb. Enter that total and your working pressure in the calculator above and it shows the Karan Micro Industries model that delivers it, from the KCS, KST and KC tables.
02Why does a compressor give less CFM at higher pressure?
Compressing air to a higher pressure takes more work, so the same motor delivers less air: Karan Micro Industries' 20 HP KCS-20 gives 80 CFM at 8 kg/cm², 65 at 10, 59 at 13 and 45 at 16. Size at the pressure you really need plus about 1 bar; each extra bar costs about 7% more energy (ELGi).
03What if my demand is larger than one compressor?
Split it across two or more machines. The calculator shows the number of units when your demand is above the largest model at that pressure; Karan Micro Industries' largest single-stage screw, the 150 HP KCS-150, delivers 724 CFM at 8 kg/cm². Two units also keep air flowing while one is serviced.
04Does the calculator choose screw or reciprocating?
It recommends a KCS rotary screw compressor and adds a KC two-stage reciprocating option when the machine runs 5 hours a day or less, because under about 4–5 loaded hours a reciprocating compressor usually costs less to own. Tick "demand rises and falls" to see the VFD screw option.