Ammeter Shunt Calculator

To make a 1 mA, 100 Ω movement read 1 A, add a shunt of 0.1001 Ω in parallel.

Extend a meter to:

Ammeter (shunt resistor)Voltmeter (series multiplier)

Meter full-scale current I_m:

Meter internal resistance R_m (Ω):

Required current range I:

Shunt resistance R_sh =

0.1001001001001 Ω

Precision

Full answer, then cut to fewer decimals (not rounded):

0.1001001001001 Ω
0.100100100100 Ω
0.10010010010 Ω
0.1001001001 Ω
0.100100100 Ω
0.10010010 Ω
0.1001001 Ω
0.100100 Ω
0.10010 Ω
0.1001 Ω
0.100 Ω
0.10 Ω
0.1 Ω

Multiplying power m = I/I_m: 1000
Current through the shunt: 0.999 A
Power in the shunt at full scale: 0.0999 W

Step-by-step solution

R_sh = I_m R_m ÷ (I − I_m) = 0.001 × 100 ÷ 0.999
R_sh = 0.1001001001 Ω = R_m ÷ (m − 1)

Ammeter Shunt Formula

R_sh = I_m R_m / (I − I_m), R_s = V/I_m − R_m

multiplying power m = I/I_m, so R_sh = R_m/(m − 1)

Worked Example

A 1 mA, 100 Ω meter extended to read 1 A:

R_sh = I_m R_m ÷ (I − I_m) = 0.001 × 100 ÷ 0.999
R_sh = 0.1001001001 Ω = R_m ÷ (m − 1)

Current through the shunt: 0.999 A · Power in the shunt at full scale: 0.0999 W

GATE tip

Loading error: a voltmeter of resistance R_v across a Thevenin source R_Th reads V × R_v/(R_v + R_Th). GATE asks for the percentage error, which is R_Th/(R_v + R_Th).

More Measurements Calculators

Wheatstone Bridge Calculator

Rₓ = R₂R₃ / R₁ at balance

Vₒᵤₜ = V_s [R₂/(R₁ + R₂) − Rₓ/(R₃ + Rₓ)]

Example: A bridge with equal 1 kΩ ratio arms balanced with R₃ = 470 Ω: Unknown resistance Rₓ = 470 Ω.

Open the wheatstone bridge calculator →
Error Propagation Calculator

Sums: ΔA + ΔB; products: ΔA/A + ΔB/B

powers: Δy/y = |n| ΔA/A; statistical errors combine as √(Σ squares)

Example: A = 100 ± 1 and B = 20 ± 0.4 multiplied, limiting errors: Result y = 2000 ± 60.

Open the error propagation calculator →

Frequently asked questions

What is voltmeter sensitivity?

1/I_m in Ω/V: a 50 µA movement gives 20 kΩ/V, so on a 10 V range the meter presents 200 kΩ to the circuit.

Why do shunts use four terminals?

For low values, contact resistance would add error; separate current and voltage terminals (Kelvin connection) remove it.

Sources

The International System of Units (SI), 9th edition (SI Brochure), Bureau International des Poids et Mesures .

Last reviewed: 2026-10-15. Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.

Cite this page

APA

Scientific Converters. (2026, October 15). Ammeter Shunt Calculator. Retrieved October 25, 2026, from https://scientificconverters.com/calculators/ammeter-shunt-calculator/

IEEE

Scientific Converters, "Ammeter Shunt Calculator," scientificconverters.com. Accessed: Oct. 25, 2026. [Online]. Available: https://scientificconverters.com/calculators/ammeter-shunt-calculator/