Enter the total volume in cubic feet (ft^3) into the TMC Calculator. The calculator will evaluate the TMC.
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TMC Formula
TMC stands for thousand million cubic feet (1 TMC = 1,000,000,000 ft³ = 28,316,846.592 m³). The calculator uses one of three formulas depending on the tab.
Unit conversion
TMC = V_m3 / 28,316,846.592
Flow rate × duration
TMC = (Q_cusec × t_days) / 11,574.074
Area × depth
TMC = (A_m2 × d_m) / 28,316,846.592
- V_m3 — volume in cubic metres
- Q_cusec — flow rate in cusecs (ft³/s)
- t_days — duration in days
- A_m2 — surface area in m²
- d_m — average depth or rainfall in metres
Inputs in other units (cumecs, L/s, acres, hectares, mm, etc.) are converted to SI before the formula is applied. The flow formula assumes a constant average rate. The area formula assumes uniform depth over the surface, so use it for reservoirs with vertical sides or as a first-pass estimate.
Reference Tables
Common TMC equivalents in other water-volume units:
| From | Equals |
|---|---|
| 1 TMC | 1,000,000,000 ft³ |
| 1 TMC | 28.317 MCM (million m³) |
| 1 TMC | 28.317 billion litres |
| 1 TMC | 22,957 acre-feet |
| 1 TMC | 11,574 cusec-days |
| 1 cusec for 1 day | 0.0000864 TMC |
| 10,000 cusecs for 1 day | 0.864 TMC |
Days required to release 1 TMC at a steady flow:
| Flow rate | Time for 1 TMC |
|---|---|
| 1,000 cusecs | 11.6 days |
| 5,000 cusecs | 2.3 days |
| 10,000 cusecs | 1.16 days (~28 hours) |
| 25,000 cusecs | 11.1 hours |
| 50,000 cusecs | 5.6 hours |
| 100,000 cusecs | 2.8 hours |
Worked Examples
Example 1 — release from a dam. A spillway discharges 15,000 cusecs for 5 days. Cusec-days = 15,000 × 5 = 75,000. TMC = 75,000 ÷ 11,574 = 6.48 TMC.
Example 2 — rainfall over a catchment. 80 mm of rain falls on a 500 km² basin. Volume = 500,000,000 m² × 0.080 m = 40,000,000 m³. TMC = 40,000,000 ÷ 28,316,847 = 1.41 TMC.
Example 3 — reservoir capacity check. A reservoir holds 5 TMC. In MCM that is 5 × 28.317 = 141.6 MCM, or about 114,785 acre-feet.
FAQ
Is TMC the same as TMC ft? Yes. TMC, TMCft, and tmcft all mean thousand million cubic feet (10⁹ ft³).
Why does cusec-day matter? Reservoir releases are reported in cusecs. Multiplying cusecs by days gives cusec-days, and 11,574 cusec-days equals 1 TMC.
Can I use this for irrigation planning? Yes for volume accounting. It does not account for evaporation, seepage, or conveyance losses.
