Compressed-air calculator

Compressed-air leaks — flow and cost per orifice

A leak is an air consumer that produces nothing — and it consumes for as long as the system is pressurised. Its flow depends on the orifice diameter and the working pressure.

This calculator estimates the free-air flow through an orifice and the corresponding annual energy cost, with a pressure-and-vacuum reference chart and field reference points.

Air leaks / orifice

Free-air flow through an orifice (leak) and annual cost — pressure & vacuum reference chart.

Regime

Pressure Compressed-air network — the leak discharges to atmosphere Vacuum Vacuum system — ambient air is drawn in through the orifice

Leak to estimate

Leak flow

Flow per leak—SCFM

Equivalent: —m³/h · —L/s
Number of leaks: —

Total flow—SCFM

The chart assumes an idealised orifice (Cd = 1.0). A real sharp-edged leak flows ≈ 0.6–0.7 of this value: adjust the Cd.

Energy cost of the leak

Based on the total leak flow: — SCFM

Estimated annual cost

Annual cost—$/yr

Energy wasted: —kWh/yr
Wasted power: —kW

Indicative cost — editable assumptions (specific power ≈ 18 kW / 100 SCFM near 7 barg, continuous operation, rate to confirm).

Sizing up a leak — field rules of thumb

A real leak has no clean bore: estimate it by its equivalent orifice. Common audit benchmarks, flow shown at 100 psig (≈ 7 barg). Example: a worn quick coupler typically leaks like a 1/16″ orifice — 5 to 6 SCFM, about 1 kW of compression wasted around the clock. “Try” loads the case into the calculator.

Typical situation	Equivalent orifice	SCFM at 100 psig
Micro-leak (pinhole, weld pore) — inaudible on the plant floor, found with an ultrasonic detector	1/64″ (0.4 mm)	0.350
Small leak — faint hiss within arm’s reach (thread, gasket, seal)	1/32″ (0.8 mm)	1.40
Typical audible leak — worn quick coupler, tired O-ring	1/16″ (1.6 mm)	5.60
Large leak — clear hiss several metres away (cracked hose, drain stuck open)	1/8″ (3.2 mm)	22.4
Major leak — burst hose, blow gun or drain valve left open	1/4″ (6.4 mm)	89.6

Indicative benchmarks (Cd = 1.0) — audibility depends on background noise: in a noisy plant (> 80 dB) most leaks below 1/16″ go unnoticed by ear, hence ultrasonic leak surveys.

Reference chart — free-air flow through an orifice

Pressure regime (free-air SCFM, Cd = 1.0)

Dia. \ psig	2	5	10	15	20	25	30	35	40	45	50	60	70	80	90	100	125	150	200
1/64″	0.024	0.040	0.061	0.079	0.096	0.113	0.129	0.145	0.161	0.177	0.193	0.225	0.256	0.287	0.319	0.350	0.428	0.506	0.661
1/32″	0.098	0.161	0.243	0.315	0.384	0.451	0.517	0.581	0.646	0.709	0.772	0.898	1.02	1.15	1.27	1.40	1.71	2.02	2.64
3/64″	0.220	0.363	0.547	0.710	0.864	1.02	1.16	1.31	1.45	1.60	1.74	2.02	2.30	2.59	2.87	3.15	3.85	4.55	5.95
1/16″	0.391	0.645	0.973	1.26	1.54	1.80	2.07	2.32	2.58	2.84	3.09	3.59	4.10	4.60	5.10	5.60	6.84	8.09	10.6
3/32″	0.879	1.45	2.19	2.84	3.45	4.06	4.65	5.23	5.81	6.38	6.95	8.09	9.22	10.3	11.5	12.6	15.4	18.2	23.8
1/8″	1.56	2.58	3.89	5.05	6.14	7.22	8.27	9.30	10.3	11.3	12.4	14.4	16.4	18.4	20.4	22.4	27.4	32.4	42.3
3/16″	3.52	5.80	8.75	11.4	13.8	16.2	18.6	20.9	23.2	25.5	27.8	32.3	36.9	41.4	45.9	50.4	61.6	72.8	95.2
1/4″	6.25	10.3	15.6	20.2	24.6	28.9	33.1	37.2	41.3	45.4	49.4	57.5	65.6	73.6	81.6	89.6	110	129	169
3/8″	14.1	23.2	35.0	45.4	55.3	65.0	74.4	83.7	93.0	102	111	129	148	166	184	202	246	291	381
1/2″	25.0	41.3	62.3	80.8	98.3	116	132	149	165	182	198	230	262	294	326	358	438	518	677
5/8″	39.1	64.5	97.3	126	154	180	207	232	258	284	309	359	410	460	510	560	684	809	1,058
3/4″	56.3	92.8	140	182	221	260	298	335	372	408	445	518	590	662	734	806	986	1,165	1,523
7/8″	76.6	126	191	247	301	354	405	456	506	556	606	704	803	901	999	1,097	1,341	1,586	2,073
1″	100	165	249	323	393	462	529	595	661	726	791	920	1,049	1,177	1,305	1,433	1,752	2,071	2,708
1 1/8″	127	209	315	409	497	585	670	753	837	919	1,001	1,164	1,328	1,490	1,652	1,814	2,217	2,621	3,427
1 1/4″	156	258	389	505	614	722	827	930	1,033	1,134	1,236	1,438	1,639	1,839	2,039	2,239	2,738	3,236	4,231
1 3/8″	189	312	471	611	743	873	1,000	1,125	1,250	1,373	1,495	1,739	1,983	2,225	2,467	2,709	3,312	3,915	5,120
1 1/2″	225	371	560	727	884	1,040	1,190	1,339	1,487	1,634	1,780	2,070	2,360	2,648	2,936	3,224	3,942	4,660	6,093
1 3/4″	306	505	763	989	1,204	1,415	1,620	1,822	2,024	2,223	2,422	2,818	3,213	3,605	3,997	4,389	5,366	6,342	8,293
2″	400	660	996	1,292	1,572	1,848	2,116	2,380	2,644	2,904	3,164	3,680	4,196	4,708	5,220	5,732	7,008	8,284	10,832

Vacuum regime (free-air SCFM, Cd = 1.0)

Dia. \ in Hg	2	4	6	8	10	12	14	18	24
1/64″	0.019	0.026	0.032	0.037	0.041	0.045	0.049	0.055	0.063
1/32″	0.075	0.105	0.128	0.148	0.165	0.181	0.195	0.220	0.252
1/16″	0.299	0.422	0.512	0.594	0.660	0.723	0.781	0.879	1.01
1/8″	1.20	1.69	2.05	2.38	2.64	2.89	3.13	3.52	4.03
1/4″	4.78	6.75	8.19	9.50	10.6	11.6	12.5	14.1	16.1
3/8″	10.8	15.2	18.4	21.4	23.8	26.0	28.1	31.6	36.3
1/2″	19.1	27.0	32.8	38.0	42.3	46.3	50.0	56.3	64.5
5/8″	29.9	42.2	51.2	59.4	66.0	72.3	78.1	87.9	101
3/4″	43.0	60.8	73.7	85.5	95.1	104	113	127	145
7/8″	58.6	82.7	100	116	129	142	153	172	198
1″	76.5	108	131	152	169	185	200	225	258

Computed values: SCFM = f(P) × (diameter in inches)². The cell nearest your input is highlighted.

Indicative estimates — validate all results before any technical decision.