CP Calculators
Quick math for the field and the office.
Standard industry formulas for first pass estimates. Change any value and the answer updates.
Pipe current requirement
Area (ft²) = π × (OD ÷ 12) × Length · I (A) = Area × Current density × (1 − Coating efficiency) ÷ 1000
Surface area0
Current required0
Underground tank current and anode count
Tank area = π × D × L + 2 × π × (D ÷ 2)² · Anodes = Current ÷ Output per anode (rounded up)
Total surface area0
Current required0
Anodes needed0
Current requirement by surface area
I (A) = Area × Current density × (1 − Coating efficiency) ÷ 1000
Current required0
In milliamps0
Magnesium anode output (Peabody)
I (mA) = C × f × Y ÷ ρ · C = 120,000 standard Mg, 150,000 high potential Mg
Output per anode0
Y = 1.0 for a coated structure polarized to the usual criterion. Use the result in the tank calculator.
Single vertical anode to earth (Dwight)
R (Ω) = (0.00521 × ρ ÷ L) × [ ln(8L ÷ d) − 1 ]
Resistance to earth0
Galvanic anode life
Life (yr) = Weight × Capacity × Utilization ÷ (8760 × Output current)
Estimated life0
Copper wire resistance and voltage drop
R = (Ω per 1000 ft at 20 °C) × Length ÷ 1000 · Drop = I × R
Wire resistance0
Voltage drop0
Soil resistivity (Wenner four pin)
ρ (Ω·cm) = 191.5 × Pin spacing (ft) × Measured R (Ω)
Soil resistivity0
Depth represented0
Rectifier sizing
V = I × R(circuit) + Back EMF · Rating = V and I × Design margin
Operating voltage0
Suggested rating0
Line current from a four wire IR drop span
R per ft = ρsteel × 12 ÷ A(steel) · I (A) = Span mV ÷ 1000 ÷ (R per ft × Span length)
Pipe resistance0
Line current0
Uses steel resistivity of 18 µΩ·cm. Sign of the current follows the sign of your reading.
Excavation or backfill volume
Volume (yd³) = Length × Width × Depth (ft) ÷ 27
Volume0
In cubic feet0
For estimating only. Field conditions govern every real design. Call 903.402.1289 for a survey or design you can build from.
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