OrderSend Error 131 in MT4/MQL4: Invalid Trade Volume Fix

OrderSend Error 131 in MT4/MQL4 means that the trade volume passed to OrderSend() is invalid. The MQL4 error name is ERR_INVALID_TRADE_VOLUME.

In most cases, the lot size is smaller than the broker’s minimum lot, larger than the maximum lot, or does not match the allowed lot step. This often appears when an EA calculates the lot size automatically.

What Does OrderSend Error 131 Mean?

• Error code: 131
• Error name: ERR_INVALID_TRADE_VOLUME
• Meaning: Invalid trade volume

Error 131 means that MT4 or the trade server rejected the requested lot size.

The relevant parameter is the trade volume supplied to OrderSend().

int ticket = OrderSend(
    Symbol(),
    OP_BUY,
    Lots,
    Ask,
    Slippage,
    StopLoss,
    TakeProfit,
    "buy order",
    Magic,
    0,
    clrBlue
);

Even when the entry signal, price, SL, and TP are valid, the order can still fail if Lots does not satisfy the symbol’s volume rules.

Common Causes of OrderSend Error 131

Check MINLOT, LOTSTEP and MAXLOT

The first step is to read the trading-volume rules for the symbol.

double minLot =
    MarketInfo(Symbol(), MODE_MINLOT);

double lotStep =
    MarketInfo(Symbol(), MODE_LOTSTEP);

double maxLot =
    MarketInfo(Symbol(), MODE_MAXLOT);

Print("Minimum lot=", minLot);
Print("Lot step=", lotStep);
Print("Maximum lot=", maxLot);

These values are symbol-specific and can differ between brokers and account types. They can also differ between FX pairs, metals, indices, and other instruments.

Lot Step Is Often the Real Cause of Error 131

A lot size can be between the minimum and maximum values and still be invalid. It must also match the allowed MODE_LOTSTEP.

For example, suppose the symbol uses:

MODE_MINLOT  = 0.01
MODE_LOTSTEP = 0.01
MODE_MAXLOT  = 50.00

The following volumes fit the 0.01 step:

0.01
0.02
0.03
0.10
1.25

But a calculated value such as:

0.037

is not aligned with a 0.01 lot step and should be adjusted before the trade request is sent.

NormalizeDouble Alone Does Not Fix LotStep

A common mistake is to use only:

lots = NormalizeDouble(lots, 2);

This changes the number of decimal places, but it does not guarantee that the value is a valid multiple of MODE_LOTSTEP.

For example, if:

MODE_LOTSTEP = 0.25

a value such as 0.30 can have valid decimal precision while still not matching the required lot increment.

MQL4 Code Example: Adjust Lot Size Automatically

The following helper functions adjust a positive lot value to the symbol’s minimum, step, and maximum conditions.

If the original calculation returns zero or a negative value, the function returns 0 instead of automatically forcing a minimum-size trade.

//+------------------------------------------------------------------+
//| Return decimal digits needed for the lot step                    |
//+------------------------------------------------------------------+
int LotDigitsByStep(double lotStep)
{
    int digits = 0;

    while(lotStep < 1.0 && digits < 8)
    {
        lotStep *= 10.0;
        digits++;
    }

    return digits;
}


//+------------------------------------------------------------------+
//| Adjust lot size to the symbol's volume rules                     |
//+------------------------------------------------------------------+
double AdjustLot(double lot)
{
    if(lot <= 0)
        return 0;

    double minLot =
        MarketInfo(Symbol(), MODE_MINLOT);

    double lotStep =
        MarketInfo(Symbol(), MODE_LOTSTEP);

    double maxLot =
        MarketInfo(Symbol(), MODE_MAXLOT);

    if(minLot <= 0 ||
       lotStep <= 0 ||
       maxLot <= 0)
    {
        Print("Invalid symbol lot settings.",
              " MinLot=", minLot,
              " LotStep=", lotStep,
              " MaxLot=", maxLot);

        return 0;
    }

    // Limit the requested volume to the broker range.
    if(lot > maxLot)
        lot = maxLot;

    // Align downward to the allowed lot step.
    lot =
        MathFloor((lot + 0.000000001) / lotStep)
        * lotStep;

    // If the adjusted value is below the minimum,
    // use the minimum lot only when the original
    // requested lot was positive.
    if(lot < minLot)
        lot = minLot;

    int lotDigits =
        LotDigitsByStep(lotStep);

    lot =
        NormalizeDouble(lot, lotDigits);

    return lot;
}

Usage example:

double calculatedLot = 0.037;

double lots =
    AdjustLot(calculatedLot);

if(lots <= 0)
{
    Print("Lot calculation is invalid.");
    return;
}

RefreshRates();

double price =
    NormalizeDouble(Ask, Digits);

ResetLastError();

int ticket = OrderSend(
    Symbol(),
    OP_BUY,
    lots,
    price,
    Slippage,
    0,
    0,
    "buy order",
    Magic,
    0,
    clrBlue
);

if(ticket < 0)
{
    int err = GetLastError();

    Print("OrderSend failed. Error=", err,
          " Lots=", lots);
}

Risk-Based Lot Calculations Can Cause Error 131

Error 131 often appears in EAs that calculate trade volume from account risk.

For example:

double lots =
    riskMoney / estimatedLossPerLot;

The mathematical result may be:

0.0374628

That number may be correct from a risk-calculation perspective but invalid as an MT4 trade volume.

The normal workflow is:

1. Calculate the raw risk-based volume.
2. Confirm that the calculation produced a positive value.
3. Read MODE_MINLOT, MODE_LOTSTEP, and MODE_MAXLOT.
4. Align the volume to the allowed lot step.
5. Check available margin.
6. Send the order.

Valid Lot Size but Not Enough Margin Is Error 134

A lot size can be structurally valid but still be too large for the account’s available margin. That is a different problem from Error 131.

You can perform an additional margin check after the volume itself has been validated.

double marginAfterTrade =
    AccountFreeMarginCheck(
        Symbol(),
        OP_BUY,
        lots
    );

if(marginAfterTrade <= 0)
{
    Print("Not enough free margin for Lots=", lots);
    return;
}

How to Debug OrderSend Error 131

When Error 131 occurs, print both the requested lot size and the symbol’s volume conditions.

double minLot =
    MarketInfo(Symbol(), MODE_MINLOT);

double lotStep =
    MarketInfo(Symbol(), MODE_LOTSTEP);

double maxLot =
    MarketInfo(Symbol(), MODE_MAXLOT);

Print("RequestedLots=", Lots);
Print("MinLot=", minLot);
Print("LotStep=", lotStep);
Print("MaxLot=", maxLot);

double adjustedLots =
    AdjustLot(Lots);

Print("AdjustedLots=", adjustedLots);

Then inspect the Experts and Journal tabs in MT4.

A practical troubleshooting order is:

1. Confirm that the actual error is 131.
2. Print the requested lot value.
3. Check MODE_MINLOT.
4. Check MODE_LOTSTEP.
5. Check MODE_MAXLOT.
6. Check the raw value returned by automatic lot calculations.
7. Align the volume to the lot step.
8. After volume validation, check margin separately.

Error 131 in MT4 Strategy Tester

OrderSend Error 131 can also occur during an MT4 Strategy Tester backtest.

The entry logic may be working correctly while the tester rejects the volume produced by the EA. This is especially common with automatic lot sizing.

Check:

• The fixed lot value in the EA inputs.
• The lot value calculated during the test.
• MODE_MINLOT for the test symbol.
• MODE_LOTSTEP for the test symbol.
• MODE_MAXLOT for the test symbol.
• Whether the calculated lot becomes zero, negative, or unusually large.

Error 129 vs 130 vs 131 vs 134

These common OrderSend errors refer to different parts of the trade request.

Related MQL4 OrderSend Guides

FAQ About OrderSend Error 131

Summary

OrderSend Error 131 in MT4/MQL4 is ERR_INVALID_TRADE_VOLUME. The fastest way to diagnose it is to compare the lot value actually passed to OrderSend() with the symbol’s minimum lot, lot step, and maximum lot.

• Error 131 means Invalid Trade Volume.
• Check MODE_MINLOT, MODE_LOTSTEP, and MODE_MAXLOT.
• A lot size can be inside the min/max range and still fail if it does not match MODE_LOTSTEP.
• NormalizeDouble() alone does not guarantee a valid lot step.
• Validate automatic risk-based lot calculations before trading.
• Do not automatically convert a failed zero/negative lot calculation into a minimum-lot trade.
• Error 131 concerns volume rules; Error 134 concerns insufficient margin.
• Print the actual lot value immediately before OrderSend() when debugging.

Back to MT4/MQL4 Technical Notes