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RPN Calculator (Reverse Polish Notation)

A free online RPN calculator with a four-level stack, LAST X, and scientific functions, in a clean modern look or a classic 1970s-style look with a red LED display.

DEG
T0
Z0
Y0
X0
0.
AMAZACALCRPN
x²
LN
LOG
ˣ√y
n!
SIN⁻¹
COS⁻¹
TAN⁻¹
e
ABS
LAST X
R↑
CLR STK
CLx
 
 
 
 
 
RCL
 
 
 
 
DEG/RAD
 
 
 
 
Δ%
 
 
 

Keyboard: 0–9 . Enter + − * / ^ yˣ Backspace Esc CLx s x⇄y r R↓ n CHS e EEX f shift

How to use an RPN calculator

In Reverse Polish Notation you enter the numbers first, then the operation. There's no = key and no parentheses. The stack holds your intermediate results.

Example: (3 + 4) × 5 = 35
  1. Press 3 ENTER
  2. Press 4 + → shows 7
  3. Press 5 × → shows 35
Example: √(3² + 4²) = 5
  1. 3 f x² → 9
  2. 4 f x² → 16 (9 moves up to Y)
  3. + → 25
  4. √x → 5

Gold labels above the keys are second functions: press f, then the key.

RPN questions

What is the stack?

Four registers named X, Y, Z, and T. X is what you see on the display. ENTER copies X up into Y so you can type the next number. Two-number operations like + and × combine Y and X, put the answer in X, and drop the rest of the stack down. Tick "Show stack" (or use the Modern style) to watch it work.

What do x⇄y, R↓, and LAST X do?

x⇄y swaps X and Y, which is handy when you entered numbers in the wrong order for − or ÷. R↓ rolls the stack down so you can see what's in each register, and R↑ rolls it up. LAST X brings back the number that was in X before the last operation, so you can fix a mistake or reuse a value.

How do percent and Δ% work?

% gives X percent of Y and leaves Y in place, so 80 ENTER 15 % shows 12 (and you can press + to get 92, the total with a 15% tip). Δ% gives the percent change from Y to X: 50 ENTER 65 f Δ% shows 30.

Why do people still use RPN?

RPN needs fewer keystrokes for long calculations, never needs parentheses, and shows intermediate results as you go, so mistakes are easier to spot. It was the standard on many engineering and finance calculators from the 1970s onward and still has loyal fans among engineers, surveyors, and pilots.

Is this an emulator of a particular calculator?

No. It's an original calculator that works the way classic RPN calculators did, with a four-level stack, ENTER, LAST X, and shifted functions. The Classic style is our own design, inspired by the look of that era.