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DG Fuel Tank Sizing Calculator

Reference: ISO 8528

⛽ ELECTRICAL

Free diesel generator fuel tank sizing calculator. Size the day tank and bulk fuel storage for a DG set from kVA rating, load factor, backup run time and specific fuel consumption.

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📋 ASSUMPTIONS & BASIS

ISO 8528

Design criteria, governing codes and assumptions.

ℹ About This Calculator

A diesel generator needs enough on-site fuel to ride through the required outage without a refill. This calculator estimates the total diesel volume from the genset kVA rating, the average load factor, the specific fuel consumption (litres per hour per kVA) and the number of hours of autonomy you must guarantee, then suggests a day-tank and bulk-tank split so you can specify tank capacity and the fill/transfer arrangement.

Specific fuel consumption depends on the engine and load — a rough figure is 0.2-0.28 L/hr per kVA at full load, and higher per-kVA at part load. Day tanks are kept small and close to the engine for safety and are topped up automatically from the bulk tank; local fire and environmental codes govern indoor tank size, bunding and separation. Always confirm the engine manufacturer fuel curve and the authority-having-jurisdiction storage limits before finalising.

DG Fuel Volume Method

ISO 8528

Step 1 - Running kVA = rated kVA x load factor.
Step 2 - Hourly fuel = running kVA x specific consumption (L/hr/kVA).
Step 3 - Total fuel = hourly fuel x required run time (hours).
Step 4 - Add a reserve (typically 10-20%) for unusable bottom volume and margin.
Step 5 - Split into a small day tank (a few hours) feeding the engine and a bulk tank for the balance.

Worked Example

A 500 kVA genset runs at 70% load factor with a specific consumption of 0.24 L/hr/kVA and must give 8 hours of autonomy. Running kVA = 500 × 0.70 = 350 kVA. Hourly fuel = 350 × 0.24 = 84 L/hr. Total = 84 × 8 = 672 L, plus ~15% reserve ≈ 775 L. A 1,000 L bulk tank with a 100–200 L day tank comfortably covers it.

DG Fuel Storage — Design Guidance

Day tank vs bulk tank

Almost all installations use a two-tank arrangement: a small day (or service) tank mounted near the engine and a larger bulk tank for the bulk of the autonomy. A transfer pump keeps the day tank topped up; the day tank is deliberately small so the indoor fire load and spill risk stay low.

How much autonomy?

Backup hours are a project decision — a few hours for a commercial standby set, 24-72 hours for a hospital or data centre, and sometimes days for critical or remote sites. Longer autonomy quickly drives large bulk tanks and refuelling logistics, so confirm the real requirement with the client.

Safety and code

Diesel storage is governed by fire and environmental codes covering tank material, bunding (secondary containment), venting, fill points and separation from the building. Size the tank with this tool, but confirm the installation details against the local authority requirements.

Frequently Asked Questions

How much diesel does a generator use per hour? +

As a rule of thumb a diesel genset burns about 0.2 to 0.28 litres per hour for every kVA at full load, less at part load. Multiply by the running kVA (rated kVA times load factor) to get the hourly consumption, then by the backup hours for total fuel.

What is a day tank and how big should it be? +

A day tank is a small tank next to the engine that feeds it directly and is refilled automatically from bulk storage. It is usually sized for a few hours of running so the engine keeps going briefly if the transfer pump fails; local fire codes cap its indoor capacity.

Should I add a reserve to the calculated fuel? +

Yes. Add roughly 10 to 20 percent for the unusable bottom volume, temperature effects and a safety margin, and round up to a standard tank size.

Does load factor matter for fuel sizing? +

Very much. A genset rarely runs at 100 percent, so using the average load factor gives realistic fuel use; sizing on full load overstates consumption and tank size and cost.

What codes govern diesel storage? +

Indoor and outdoor diesel storage, bunding, venting and separation distances are set by local fire and environmental regulations (for example NFPA 30/37 and national petroleum rules). Confirm limits with the authority having jurisdiction.